Starting release 0.7.0

[parrot.git] / src / mmd.c

/*
Copyright (C) 2003-2008, The Perl Foundation.
$Id$

=head1 NAME

src/mmd.c - Multimethod dispatch for binary opcode functions

=head1 SYNOPSIS

This system is set up to handle type-based dispatching for binary (two
argument) functions. This includes, though isn't necessarily limited to, binary
operators such as addition or subtraction.

=head1 DESCRIPTION

The MMD system is straightforward, and currently must be explicitly invoked,
for example by a vtable function. (We reserve the right to use MMD in all
circumstances, but currently do not).

=head2 API

For the purposes of the API, each MMD-able function is assigned a unique
number which is used to find the correct function table. This is the
C<func_num> parameter in the following functions. While Parrot isn't
restricted to a predefined set of functions, it I<does> set things up so
that all the binary vtable functions have a MMD table preinstalled for
them, with default behaviour.

=head2 Remarks

C<< binop_mmd_funcs->x >> and C<< ->y >> are table sizes
not highest type in table.

=head2 Functions

=over 4

=cut

*/

#include "parrot/compiler.h"
#include "parrot/parrot.h"
#include "parrot/mmd.h"
#include "parrot/oplib/ops.h"
#include "mmd.str"

/* HEADERIZER HFILE: include/parrot/mmd.h */

/* HEADERIZER BEGIN: static */
/* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */

static INTVAL distance_cmp(SHIM_INTERP, INTVAL a, INTVAL b);
static void dump_mmd(PARROT_INTERP, INTVAL function)
        __attribute__nonnull__(1);

PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
static funcptr_t get_mmd_dispatcher(PARROT_INTERP,
    ARGIN(PMC *left),
    ARGIN(PMC *right),
    INTVAL function,
    ARGOUT(int *is_pmc))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3)
        __attribute__nonnull__(5)
        FUNC_MODIFIES(*is_pmc);

PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
static PMC* mmd_arg_tuple_func(PARROT_INTERP)
        __attribute__nonnull__(1);

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_arg_tuple_inline(PARROT_INTERP,
    ARGIN(STRING *signature),
    va_list args)
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

static void mmd_create_builtin_multi_meth(PARROT_INTERP,
    ARGIN(PMC *ns),
    INTVAL type,
    ARGIN(const MMD_init *entry))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(4);

static void mmd_create_builtin_multi_meth_2(PARROT_INTERP,
    ARGIN(PMC *ns),
    INTVAL func_nr,
    INTVAL type,
    INTVAL right,
    funcptr_t func_ptr)
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_cvt_to_types(PARROT_INTERP, ARGIN(PMC *multi_sig))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

PARROT_CANNOT_RETURN_NULL
static PMC * mmd_deref(PARROT_INTERP, ARGIN(PMC *value))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

static UINTVAL mmd_distance(PARROT_INTERP,
    ARGIN(PMC *pmc),
    ARGIN(PMC *arg_tuple))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

static void mmd_ensure_writable(PARROT_INTERP,
    INTVAL function,
    ARGIN_NULLOK(const PMC *pmc))
        __attribute__nonnull__(1);

static void mmd_expand_x(PARROT_INTERP, INTVAL func_nr, INTVAL new_x)
        __attribute__nonnull__(1);

static void mmd_expand_y(PARROT_INTERP, INTVAL func_nr, INTVAL new_y)
        __attribute__nonnull__(1);

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_get_ns(PARROT_INTERP)
        __attribute__nonnull__(1);

PARROT_WARN_UNUSED_RESULT
static int mmd_is_hidden(PARROT_INTERP, ARGIN(PMC *multi), ARGIN(PMC *cl))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_make_ns(PARROT_INTERP)
        __attribute__nonnull__(1);

static int mmd_maybe_candidate(PARROT_INTERP,
    ARGIN(PMC *pmc),
    ARGIN(PMC *cl))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

static void mmd_search_builtin(PARROT_INTERP,
    ARGIN(STRING *meth),
    ARGIN(PMC *cl))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

static void mmd_search_classes(PARROT_INTERP,
    ARGIN(STRING *meth),
    ARGIN(PMC *arg_tuple),
    ARGIN(PMC *cl),
    INTVAL start_at_parent)
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3)
        __attribute__nonnull__(4);

static int mmd_search_cur_namespace(PARROT_INTERP,
    ARGIN(STRING *meth),
    ARGIN(PMC *cl))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

PARROT_CAN_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_search_default(PARROT_INTERP,
    ARGIN(STRING *meth),
    ARGIN(PMC *arg_tuple))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC* mmd_search_scopes(PARROT_INTERP, ARGIN(STRING *meth))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

static void mmd_sort_candidates(PARROT_INTERP,
    ARGIN(PMC *arg_tuple),
    ARGIN(PMC *cl))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        __attribute__nonnull__(3);

/* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */
/* HEADERIZER END: static */


#define MMD_DEBUG 0

#ifndef NDEBUG
/*

=item C<static void dump_mmd>

RT #48260: Not yet documented!!!

=cut

*/

static void
dump_mmd(PARROT_INTERP, INTVAL function)
{
    UINTVAL x, y;
    UINTVAL offset;
    MMD_table * const table = interp->binop_mmd_funcs + function;
    funcptr_t func;
    const UINTVAL x_funcs = table->x;
    const UINTVAL y_funcs = table->y;

    printf("    ");
    for (x = 0; x < x_funcs; ++x) {
        if (x % 10)
            printf(" ");
        else
            printf("%d", (int) x / 10);
    }

    printf("\n");

    for (y = 0; y < y_funcs; ++y) {
        printf("%3d ", (int)y);
        for (x = 0; x < x_funcs; ++x) {
            offset = x_funcs * y + x;
            func   = table->mmd_funcs[offset];

            printf("%c",
                    (UINTVAL)func & 1 ?  'P' :
                    !func  ? '0' : 'F');
        }

        printf("\n");
    }

    for (y = 0; y < y_funcs; ++y) {
        for (x = 0; x < x_funcs; ++x) {
            offset = x_funcs * y + x;
            func   = table->mmd_funcs[offset];

            if (func && !((UINTVAL) func & 1))
                printf("%3d %3d: %p\n", (int)x, (int)y, (void*) func);
        }
    }
}
#endif


/*

=item C<funcptr_t get_mmd_dispatch_type>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_API
PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
funcptr_t
get_mmd_dispatch_type(PARROT_INTERP, INTVAL func_nr, INTVAL left_type,
        INTVAL right_type, ARGOUT(int *is_pmc))
{
    funcptr_t         func    = NULL;
    MMD_table * const table   = interp->binop_mmd_funcs + func_nr;
    const UINTVAL     x_funcs = table->x;
    const UINTVAL     y_funcs = table->y;
    INTVAL            r       = right_type;
    funcptr_t         func_;

#if MMD_DEBUG
    fprintf(stderr, "running function %d with left type=%u, right type=%u\n",
        (int) func_nr, (unsigned) left_type, (unsigned) right_type);
#endif

    PARROT_ASSERT(left_type >= 0);
    PARROT_ASSERT(right_type >=0 ||
            (right_type >= enum_type_INTVAL && right_type <= enum_type_PMC));

    if (right_type < 0)
        right_type -= enum_type_INTVAL;
    else
        right_type += 4;

    if ((UINTVAL)left_type < x_funcs && (UINTVAL)right_type < y_funcs) {
        const UINTVAL offset = x_funcs * right_type + left_type;
        func                 = table->mmd_funcs[offset];
    }

    if (!func) {
        const char * const meth_c = Parrot_MMD_method_name(interp, func_nr);
        STRING     * const meth_s = const_string(interp, meth_c);
        PMC        * const method = Parrot_MMD_search_default_infix(interp,
                                        meth_s, left_type, r);
        if (!method)
            Parrot_ex_throw_from_c_args(interp, 0, 1, "MMD function %s not found "
                "for types (%d, %d)", meth_c, left_type, r);


        if (method->vtable->base_type == enum_class_NCI) {
            /* C function is at struct_val */
            func    = D2FPTR(PMC_struct_val(method));
            *is_pmc = 0;
            mmd_register(interp, func_nr, left_type, r,
                    (funcptr_t)PMC_struct_val(method));
        }
        else {
            *is_pmc = 1;
            func    = D2FPTR(method);
            mmd_register_sub(interp, func_nr, left_type, r, method);
        }

        return func;
    }

    *is_pmc = (UINTVAL)func & 3;
    func_   = (funcptr_t)((UINTVAL)func & ~3);

#ifndef PARROT_HAS_ALIGNED_FUNCPTR
    if (!*is_pmc) {
        return func;
    }
    else if (!is_pmc_ptr(interp, F2DPTR(func_))) {
        *is_pmc = 0;
        return func;
    }
#endif
    return func_;
}


/*

=item C<static funcptr_t get_mmd_dispatcher>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
static funcptr_t
get_mmd_dispatcher(PARROT_INTERP, ARGIN(PMC *left), ARGIN(PMC *right),
        INTVAL function, ARGOUT(int *is_pmc))
{
    const UINTVAL left_type  = VTABLE_type(interp, left);
    const UINTVAL right_type = VTABLE_type(interp, right);
    return get_mmd_dispatch_type(interp, function, left_type, right_type,
            is_pmc);
}


/*

=item C<static PMC * mmd_deref>

If C<value> is a reference-like PMC, dereference it so we can make an MMD
call on the 'real' value.

=cut

*/

PARROT_CANNOT_RETURN_NULL
static PMC *
mmd_deref(PARROT_INTERP, ARGIN(PMC *value))
{
    if (!PObj_is_object_TEST(value)
    &&  VTABLE_type(interp, value) != value->vtable->base_type)
        return VTABLE_get_pmc(interp, value);
    else
        return value;
}


/*

=item C<static void mmd_ensure_writable>

Make sure C<pmc> is writable enough for C<function>.

=cut

*/

static void
mmd_ensure_writable(PARROT_INTERP, INTVAL function, ARGIN_NULLOK(const PMC *pmc))
{
    if (!PMC_IS_NULL(pmc) && (pmc->vtable->flags & VTABLE_IS_READONLY_FLAG))
        Parrot_ex_throw_from_c_args(interp, 0, 1, "%s applied to read-only argument",
            Parrot_MMD_method_name(interp, function));
}


/*

=item C<PMC* mmd_dispatch_p_ppp>

Dispatch to a multimethod that returns a PMC. C<left>, C<right>, and
C<dest> are all PMC pointers, while C<func_num> is the MMD table that
should be used to do the dispatching.
If the C<dest> pointer is NULL, it dispatches two a two-argument function
that returns a new C<dest> always.

The MMD system will figure out which function should be called based on
the types of C<left> and C<right> and call it, passing in C<left>,
C<right>, and possibly C<dest> like any other binary vtable function.

=cut

*/

PARROT_API
PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
PMC*
mmd_dispatch_p_ppp(PARROT_INTERP, ARGIN(PMC *left), ARGIN(PMC *right),
        ARGIN_NULLOK(PMC *dest), INTVAL func_nr)
{
    mmd_f_p_ppp real_function;
    int         is_pmc;

    left  = mmd_deref(interp, left);
    right = mmd_deref(interp, right);

    real_function = (mmd_f_p_ppp)get_mmd_dispatcher(interp,
            left, right, func_nr, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC*)real_function;
        if (dest)
            return Parrot_runops_fromc_args(interp, sub, "PPPP",
                    left, right, dest);
        else
            return Parrot_runops_fromc_args(interp, sub, "PPP", left, right);
    }

    return (*real_function)(interp, left, right, dest);
}


/*

=item C<PMC* mmd_dispatch_p_pip>

Like C<mmd_dispatch_p_ppp>, right argument is a native INTVAL.

=cut

*/

PARROT_API
PARROT_CAN_RETURN_NULL
PMC*
mmd_dispatch_p_pip(PARROT_INTERP,
        ARGIN(PMC *left), INTVAL right, ARGIN_NULLOK(PMC *dest), INTVAL func_nr)
{
    int         is_pmc;
    UINTVAL     left_type;
    mmd_f_p_pip real_function;

    left      = mmd_deref(interp, left);
    left_type = VTABLE_type(interp, left);

    real_function =
        (mmd_f_p_pip)get_mmd_dispatch_type(interp, func_nr, left_type,
                                           enum_type_INTVAL, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC *)real_function;
        if (dest)
            return Parrot_runops_fromc_args(interp, sub, "PPIP",
                    left, right, dest);
        else
            return Parrot_runops_fromc_args(interp, sub, "PPI", left, right);
    }

    return (*real_function)(interp, left, right, dest);
}


/*

=item C<PMC* mmd_dispatch_p_pnp>

Like C<mmd_dispatch_p_ppp>, right argument is a native FLOATVAL.

=cut

*/

PARROT_API
PARROT_CAN_RETURN_NULL
PMC*
mmd_dispatch_p_pnp(PARROT_INTERP,
        ARGIN(PMC *left), FLOATVAL right, ARGIN_NULLOK(PMC *dest), INTVAL func_nr)
{
    mmd_f_p_pnp real_function;
    int         is_pmc;
    UINTVAL     left_type;

    left          = mmd_deref(interp, left);
    left_type     = VTABLE_type(interp, left);

    real_function = (mmd_f_p_pnp)get_mmd_dispatch_type(interp,
            func_nr, left_type, enum_type_FLOATVAL, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC*)real_function;
        if (dest)
            return Parrot_runops_fromc_args(interp, sub, "PPNP",
                    left, right, dest);
        else
            return Parrot_runops_fromc_args(interp, sub, "PPN", left, right);
    }

    return (*real_function)(interp, left, right, dest);
}


/*

=item C<PMC* mmd_dispatch_p_psp>

Like C<mmd_dispatch_p_ppp>, right argument is a native STRING *.

=cut

*/

PARROT_API
PARROT_CAN_RETURN_NULL
PMC*
mmd_dispatch_p_psp(PARROT_INTERP, ARGIN(PMC *left), ARGIN(STRING *right),
        ARGIN_NULLOK(PMC *dest), INTVAL func_nr)
{
    int               is_pmc;
    const UINTVAL     left_type     = VTABLE_type(interp, left);
    const mmd_f_p_psp real_function =
        (mmd_f_p_psp)get_mmd_dispatch_type(interp,
            func_nr, left_type, enum_type_STRING, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC*)real_function;
        if (dest)
            return Parrot_runops_fromc_args(interp, sub, "PPSP",
                    left, right, dest);
        else
            return Parrot_runops_fromc_args(interp, sub, "PPS", left, right);
    }

    return (*real_function)(interp, left, right, dest);
}


/*

=item C<void mmd_dispatch_v_pp>

Inplace dispatch function for C<< left <op=> right >>.

=cut

*/

PARROT_API
void
mmd_dispatch_v_pp(PARROT_INTERP,
        ARGIN(PMC *left), ARGIN(PMC *right), INTVAL func_nr)
{
    mmd_f_v_pp real_function;
    int        is_pmc;

    left  = mmd_deref(interp, left);
    right = mmd_deref(interp, right);

    mmd_ensure_writable(interp, func_nr, left);

    real_function = (mmd_f_v_pp)get_mmd_dispatcher(interp,
            left, right, func_nr, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC*)real_function;
        Parrot_runops_fromc_args(interp, sub, "vPP", left, right);
    }

    (*real_function)(interp, left, right);
}


/*

=item C<void mmd_dispatch_v_pi>

Inplace dispatch function for C<< left <op=> right >>.

=cut

*/

PARROT_API
void
mmd_dispatch_v_pi(PARROT_INTERP,
        ARGIN(PMC *left), INTVAL right, INTVAL func_nr)
{
    int        is_pmc;
    UINTVAL    left_type;
    mmd_f_v_pi real_function;

    left = mmd_deref(interp, left);
    mmd_ensure_writable(interp, func_nr, left);

    left_type     = VTABLE_type(interp, left);
    real_function = (mmd_f_v_pi)get_mmd_dispatch_type(interp,
            func_nr, left_type, enum_type_INTVAL, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC *)real_function;
        Parrot_runops_fromc_args(interp, sub, "vPI", left, right);
    }

    (*real_function)(interp, left, right);
}


/*

=item C<void mmd_dispatch_v_pn>

Inplace dispatch function for C<< left <op=> right >>.

=cut

*/

PARROT_API
void
mmd_dispatch_v_pn(PARROT_INTERP,
        ARGIN(PMC *left), FLOATVAL right, INTVAL func_nr)
{
    int        is_pmc;
    UINTVAL    left_type;
    mmd_f_v_pn real_function;

    left = mmd_deref(interp, left);
    mmd_ensure_writable(interp, func_nr, left);

    left_type     = VTABLE_type(interp, left);
    real_function = (mmd_f_v_pn)get_mmd_dispatch_type(interp,
            func_nr, left_type, enum_type_FLOATVAL, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC *)real_function;
        Parrot_runops_fromc_args(interp, sub, "vPN", left, right);
    }

    (*real_function)(interp, left, right);
}


/*

=item C<void mmd_dispatch_v_ps>

Inplace dispatch function for C<< left <op=> right >>.

=cut

*/

PARROT_API
void
mmd_dispatch_v_ps(PARROT_INTERP,
        ARGIN(PMC *left), ARGIN(STRING *right), INTVAL func_nr)
{
    int        is_pmc;
    UINTVAL    left_type;
    mmd_f_v_ps real_function;

    left = mmd_deref(interp, left);
    mmd_ensure_writable(interp, func_nr, left);

    left_type     = VTABLE_type(interp, left);
    real_function = (mmd_f_v_ps)get_mmd_dispatch_type(interp,
            func_nr, left_type, enum_type_STRING, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC *)real_function;
        Parrot_runops_fromc_args(interp, sub, "vPS", left, right);
    }

    (*real_function)(interp, left, right);
}


/*

=item C<INTVAL mmd_dispatch_i_pp>

Like C<mmd_dispatch_p_ppp()>, only it returns an C<INTVAL>. This is used
by MMD compare functions.

=cut

*/

PARROT_API
INTVAL
mmd_dispatch_i_pp(PARROT_INTERP,
        ARGIN(PMC *left), ARGIN(PMC *right), INTVAL func_nr)
{
    int        is_pmc;
    mmd_f_i_pp real_function;

    left  = mmd_deref(interp, left);
    right = mmd_deref(interp, right);

    real_function = (mmd_f_i_pp)get_mmd_dispatcher(interp,
            left, right, func_nr, &is_pmc);

    if (is_pmc) {
        PMC * const sub = (PMC *)real_function;
        return Parrot_runops_fromc_args_reti(interp, sub, "IPP",
                left, right);
    }

    return (*real_function)(interp, left, right);
}


/*

=item C<void mmd_add_function>

Add a new binary MMD function to the list of functions the MMD system knows
of. C<func_num> is the number of the new function. C<function> is ignored.

RT #45941 change this to a MMD register interface that takes a function *name*.

=cut

*/

PARROT_API
void
mmd_add_function(PARROT_INTERP, INTVAL func_nr, SHIM(funcptr_t function))
{
    /* XXX Something looks wrong here.  n_binop_mmd_funcs gets incremented,
     * but the function doesn't get saved */
    if (func_nr >= (INTVAL)interp->n_binop_mmd_funcs) {
        INTVAL i;
        mem_realloc_n_typed(interp->binop_mmd_funcs, func_nr+1, MMD_table);

        for (i = interp->n_binop_mmd_funcs; i <= func_nr; ++i)  {
            MMD_table * const table = interp->binop_mmd_funcs + i;

            table->x         = 0;
            table->y         = 0;
            table->mmd_funcs = NULL;
        }

        interp->n_binop_mmd_funcs = func_nr + 1;
    }
}


/*

=item C<static void mmd_expand_x>

Expands the function table in the X dimension to include C<new_x>.

=cut

*/

static void
mmd_expand_x(PARROT_INTERP, INTVAL func_nr, INTVAL new_x)
{
    funcptr_t *new_table;
    UINTVAL x;
    UINTVAL y;
    UINTVAL i;
    char *src_ptr, *dest_ptr;
    size_t old_dp, new_dp;
    MMD_table * const table = interp->binop_mmd_funcs + func_nr;

    /* Is the Y 0? If so, nothing to expand, so just set the X for later use */
    if (table->y == 0) {
        table->x = new_x;
        return;
    }

    /* The Y is not zero. Bleah. This means we have to expand the
       table in an unpleasant way. */

    x = table->x;
    y = table->y;

    /* First, fill in the whole new table with the default function
       pointer. We only really need to do the new part, but... */
    new_table = mem_allocate_n_zeroed_typed(y * new_x, funcptr_t);

    /* Then copy the old table over. We have to do this row by row,
       because the rows in the old and new tables are different lengths */
    src_ptr  = (char *)table->mmd_funcs;
    dest_ptr = (char *)new_table;
    old_dp   = sizeof (funcptr_t) * x;
    new_dp   = sizeof (funcptr_t) * new_x;

    for (i = 0; i < y; i++) {
        STRUCT_COPY_N(dest_ptr, src_ptr, x);
        src_ptr  += old_dp;
        dest_ptr += new_dp;
    }

    if (table->mmd_funcs)
        mem_sys_free(table->mmd_funcs);

    table->x = new_x;

    /* Set the old table to point to the new table */
    table->mmd_funcs = new_table;
}


/*

=item C<static void mmd_expand_y>

Expands the function table in the Y direction.

=cut

*/

static void
mmd_expand_y(PARROT_INTERP, INTVAL func_nr, INTVAL new_y)
{
    UINTVAL           new_size, old_size;
    MMD_table * const table = interp->binop_mmd_funcs + func_nr;

    PARROT_ASSERT(table->x);

    old_size = sizeof (funcptr_t) * table->x * table->y;
    new_size = sizeof (funcptr_t) * table->x * new_y;

    if (table->mmd_funcs)
        table->mmd_funcs = (funcptr_t *)mem_sys_realloc_zeroed(
            table->mmd_funcs, new_size, old_size);
    else
        table->mmd_funcs = (funcptr_t *)mem_sys_allocate_zeroed(new_size);

    table->y = new_y;
}


/*

=item C<void mmd_add_by_class>

Add a function to the MMD table by class name, rather than class number.
Handles the case where the named class isn't loaded yet.

Adds a new MMD function C<funcptr> to the C<func_num> function table
that will be invoked when the left parameter is of class C<left_class>
and the right parameter is of class C<right_class>. Both classes are
C<STRING *>s that hold the PMC class names for the left and right sides.
If either class isn't yet loaded, Parrot will cache the information such
that the function will be installed if at some point in the future both
classes are available.

Currently this is done by just assigning class numbers to the classes,
which the classes will pick up and use if they're later loaded, but we
may later put the functions into a deferred table that we scan when PMC
classes are loaded. Either way, the function will be guaranteed to be
installed when it's needed.

The function table must exist, but if it is too small, it will
automatically be expanded.

=cut

*/

PARROT_API
void
mmd_add_by_class(PARROT_INTERP,
             INTVAL functype,
             ARGIN(STRING *left_class), ARGIN(STRING *right_class),
             NULLOK(funcptr_t funcptr))
{
    INTVAL left_type  = pmc_type(interp, left_class);
    INTVAL right_type = pmc_type(interp, right_class);

    if (left_type == enum_type_undef)
        left_type = pmc_register(interp, left_class);

    if (right_type == enum_type_undef)
        right_type = pmc_register(interp, right_class);

    mmd_register(interp, functype, left_type, right_type, funcptr);

}


/*

=item C<void mmd_register>

Register a function C<funcptr> for MMD function table C<func_num> for classes
C<left_type> and C<right_type>. The left and right types are C<INTVAL>s that
represent the class ID numbers.

The function table must exist, but if it is too small, it will
automatically be expanded.

Adding a new function to the table can be interestingly non-trivial, so
we get to be tricky.

If the left or right types are larger than anything we've seen so far,
it means that we have to expand the table. Making Y larger is simple --
just realloc with some more rows. Making X larger is less simple. In
either case, we punt to other functions.

RT #45943 - Currently the MMD system doesn't handle inheritance and best match
searching, as it assumes that all PMC types have no parent type. This
can be considered a bug, and will be resolved at some point in the
future.

=cut

*/

PARROT_API
void
mmd_register(PARROT_INTERP, INTVAL func_nr, INTVAL left_type, INTVAL right_type,
             NULLOK(funcptr_t funcptr))
{

    INTVAL     offset;
    MMD_table *table;

    PARROT_ASSERT(func_nr < (INTVAL)interp->n_binop_mmd_funcs);
    PARROT_ASSERT(left_type >= 0);
    PARROT_ASSERT(right_type >=0 ||
            (right_type >= enum_type_INTVAL && right_type <= enum_type_PMC));

    if (right_type < 0)
        right_type -= enum_type_INTVAL;
    else
        right_type += 4;

    table = interp->binop_mmd_funcs + func_nr;

    if ((INTVAL)table->x <= left_type)
        mmd_expand_x(interp, func_nr, left_type + 1);

    if ((INTVAL)table->y <= right_type)
        mmd_expand_y(interp, func_nr, right_type + 1);

    offset = table->x * right_type + left_type;
    table->mmd_funcs[offset] = funcptr;
}


/*

=item C<void mmd_register_sub>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_API
void
mmd_register_sub(PARROT_INTERP, INTVAL func_nr,
             INTVAL left_type, INTVAL right_type, ARGIN(const PMC *sub))
{
    /* returned from mmdvt_find */
    if (sub->vtable->base_type == enum_class_NCI) {
        mmd_register(interp, func_nr, left_type, right_type,
                D2FPTR(PMC_struct_val(sub)));
    }
    else {
        PMC * const fake = (PMC *)((UINTVAL) sub | 1);
        mmd_register(interp, func_nr, left_type, right_type, D2FPTR(fake));
    }
}


/*

=item C<void mmd_destroy>

Frees all the memory allocated used the MMD subsystem.

=cut

*/

PARROT_API
void
mmd_destroy(PARROT_INTERP)
{
    if (interp->n_binop_mmd_funcs) {
        UINTVAL i;
        for (i = 0; i <interp->n_binop_mmd_funcs; ++i) {
            if (interp->binop_mmd_funcs[i].mmd_funcs) {
                mem_sys_free(interp->binop_mmd_funcs[i].mmd_funcs);
                interp->binop_mmd_funcs[i].mmd_funcs = NULL;
            }
        }
    }
    mem_sys_free(interp->binop_mmd_funcs);
    interp->binop_mmd_funcs = NULL;
}


/*

=item C<PMC * mmd_vtfind>

Return an MMD PMC function for the given data types. The return result is
either a Sub PMC (for PASM MMD functions) or a NCI PMC holding the
C function pointer in PMC_struct_val.

=cut

*/

PARROT_API
PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
PMC *
mmd_vtfind(PARROT_INTERP, INTVAL func_nr, INTVAL left, INTVAL right)
{
    int             is_pmc;
    const funcptr_t func = get_mmd_dispatch_type(interp,
            func_nr, left, right, &is_pmc);
    PMC            *f;

    /* RT #45945 if is_pmc == 2 a Bound_NCI is returned, which actually should
     * be filled with one of the wrapper functions */
    if (func && is_pmc)
        return (PMC *)F2DPTR(func);

    f                 = pmc_new(interp, enum_class_NCI);
    VTABLE_set_pointer(interp, f, F2DPTR(func));
    return f;
}


/*

=item C<PMC * Parrot_MMD_search_default_infix>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_API
PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
PMC *
Parrot_MMD_search_default_infix(PARROT_INTERP, ARGIN(STRING *meth),
        INTVAL left_type, INTVAL right_type)
{
    PMC* const arg_tuple = pmc_new(interp, enum_class_FixedIntegerArray);

    VTABLE_set_integer_native(interp,    arg_tuple, 2);
    VTABLE_set_integer_keyed_int(interp, arg_tuple, 0, left_type);
    VTABLE_set_integer_keyed_int(interp, arg_tuple, 1, right_type);

    return mmd_search_default(interp, meth, arg_tuple);
}


/*

=item C<PMC * Parrot_mmd_sort_candidate_list>

Given an array PMC (usually a MultiSub) sort the mmd candidates by their
manhatten distance to the current args.

=cut

*/

PARROT_API
PARROT_CAN_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
PMC *
Parrot_mmd_sort_candidate_list(PARROT_INTERP, ARGIN(PMC *candidates))
{
    PMC   *arg_tuple;
    INTVAL n = VTABLE_elements(interp, candidates);

    if (!n)
        return PMCNULL;

    arg_tuple  = mmd_arg_tuple_func(interp);
    candidates = VTABLE_clone(interp, candidates);

    mmd_sort_candidates(interp, arg_tuple, candidates);

    /* if there aren't any variants that match the current args, we could end
       up with an empty list */
    n = VTABLE_elements(interp, candidates);

    if (!n)
        return PMCNULL;

    return candidates;
}


/*

=item C<static PMC* mmd_arg_tuple_inline>

Return a list of argument types. PMC arguments are specified as function
arguments.

=cut
*/

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_arg_tuple_inline(PARROT_INTERP, ARGIN(STRING *signature), va_list args)
{
    INTVAL       i;
    PMC * const  arg_tuple = pmc_new(interp, enum_class_FixedIntegerArray);
    const INTVAL sig_len   = string_length(interp, signature);

    if (!sig_len)
        return arg_tuple;

    VTABLE_set_integer_native(interp, arg_tuple, sig_len);

    for (i = 0; i < sig_len; ++i) {
        INTVAL type = string_index(interp, signature, i);
        switch (type) {
            case 'I':
                VTABLE_set_integer_keyed_int(interp, arg_tuple,
                        i, enum_type_INTVAL);
                break;
            case 'N':
                VTABLE_set_integer_keyed_int(interp, arg_tuple,
                        i, enum_type_FLOATVAL);
                break;
            case 'S':
                VTABLE_set_integer_keyed_int(interp, arg_tuple,
                        i, enum_type_STRING);
                break;
            case 'O':
            case 'P':
            {
                PMC *arg = va_arg(args, PMC *);
                type     = VTABLE_type(interp, arg);
                VTABLE_set_integer_keyed_int(interp, arg_tuple, i, type);
                break;
            }
            default:
                Parrot_ex_throw_from_c_args(interp, NULL, 1,
                    "Unknown signature type %d in mmd_arg_tuple", type);
                break;
        }

    }
    return arg_tuple;
}


/*

=item C<static PMC* mmd_arg_tuple_func>

Return a list of argument types. PMC arguments are take from registers
according to calling conventions.

=cut

*/

PARROT_WARN_UNUSED_RESULT
PARROT_CANNOT_RETURN_NULL
static PMC*
mmd_arg_tuple_func(PARROT_INTERP)
{
    INTVAL sig_len, i, type;
    PMC                *arg;
    PMC                *args_array;    /* from recent set_args opcode */
    PackFile_Constant **constants;

    /*
     * if there is no signature e.g. because of
     *      m = getattribute l, "__add"
     * - we have to return the MultiSub
     * - create a BoundMulti
     * - dispatch in invoke - yeah ugly
     */

    PMC * const arg_tuple = pmc_new(interp, enum_class_ResizableIntegerArray);
    opcode_t   *args_op   = interp->current_args;

    if (!args_op)
        return arg_tuple;

    PARROT_ASSERT(*args_op == PARROT_OP_set_args_pc);
    constants  = interp->code->const_table->constants;
    ++args_op;
    args_array = constants[*args_op]->u.key;

    ASSERT_SIG_PMC(args_array);

    sig_len = SIG_ELEMS(args_array);
    if (!sig_len)
        return arg_tuple;

    ++args_op;

    for (i = 0; i < sig_len; ++i, ++args_op) {
        type = SIG_ITEM(args_array, i);

        /* named don't MMD */
        if (type & PARROT_ARG_NAME)
            break;
        switch (type & (PARROT_ARG_TYPE_MASK | PARROT_ARG_FLATTEN)) {
            case PARROT_ARG_INTVAL:
                VTABLE_push_integer(interp, arg_tuple, enum_type_INTVAL);
                break;
            case PARROT_ARG_FLOATVAL:
                VTABLE_push_integer(interp, arg_tuple, enum_type_FLOATVAL);
                break;
            case PARROT_ARG_STRING:
                VTABLE_push_integer(interp, arg_tuple, enum_type_STRING);
                break;
            case PARROT_ARG_PMC:
                {
                const int idx = *args_op;
                if ((type & PARROT_ARG_CONSTANT))
                    arg = constants[idx]->u.key;
                else
                    arg = REG_PMC(interp, idx);
                type = VTABLE_type(interp, arg);
                VTABLE_push_integer(interp, arg_tuple, type);
                }
                break;
            case PARROT_ARG_FLATTEN | PARROT_ARG_PMC:  {
                /* expand flattening args */
                int j, n;

                const int idx = *args_op;
                arg           = REG_PMC(interp, idx);
                n             = VTABLE_elements(interp, arg);

                for (j = 0; j < n; ++j)  {
                    PMC * const elem = VTABLE_get_pmc_keyed_int(interp, arg, j);
                    type             = VTABLE_type(interp, elem);
                    VTABLE_push_integer(interp, arg_tuple, type);
                }
                break;
            }
            default:
                Parrot_ex_throw_from_c_args(interp, NULL, 1,
                    "Unknown signature type %d in mmd_arg_tuple", type);
                break;
        }
    }


    return arg_tuple;
}


/*

=item C<static PMC* mmd_search_default>

Default implementation of MMD search. Search scopes for candidates, walk the
class hierarchy, sort all candidates by their Manhattan distance, and return
result

=cut

*/

PARROT_CAN_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_search_default(PARROT_INTERP, ARGIN(STRING *meth), ARGIN(PMC *arg_tuple))
{
    /* 2) create a list of matching functions */
    PMC * const candidate_list = mmd_search_scopes(interp, meth);

    /*
     * 3) if list is empty fail
     *    if the first found function is a plain Sub: finito
     */
    INTVAL n = VTABLE_elements(interp, candidate_list);

    if (n == 1) {
        PMC    * const pmc  = VTABLE_get_pmc_keyed_int(interp, candidate_list, 0);
        STRING * const _sub = CONST_STRING(interp, "Sub");

        if (VTABLE_isa(interp, pmc, _sub))
            return pmc;
    }

    /*
     * 4) first was a MultiSub - go through all found MultiSubs and check
     *    the first arguments MRO, add all MultiSubs and plain methods,
     *    where the first argument matches
     */
    mmd_search_classes(interp, meth, arg_tuple, candidate_list, 0);
    n = VTABLE_elements(interp, candidate_list);
    if (!n)
        return NULL;

    /* 5) sort the list */

    if (n > 1)
        mmd_sort_candidates(interp, arg_tuple, candidate_list);

    n = VTABLE_elements(interp, candidate_list);

    if (!n)
        return NULL;

    /* 6) Uff, return first one */
    return VTABLE_get_pmc_keyed_int(interp, candidate_list, 0);
}


/*

=item C<static void mmd_search_classes>

Search all the classes in all MultiSubs of the candidates C<cl> and return
a list of all candidates. C<start_at_parent> is 0 to start at the class itself
or 1 to search from the first parent class.

=cut

*/

static void
mmd_search_classes(PARROT_INTERP, ARGIN(STRING *meth),
        ARGIN(PMC *arg_tuple), ARGIN(PMC *cl), INTVAL start_at_parent)
{
    INTVAL type1;

    /* get the class of the first argument */
    if (!VTABLE_elements(interp, arg_tuple))
        return;

    type1 = VTABLE_get_integer_keyed_int(interp, arg_tuple, 0);

    if (type1 < 0) {
        return;
        /* RT #45947 create some class namespace */
    }
    else {
        PMC * const  mro = interp->vtables[type1]->mro;
        const INTVAL n   = VTABLE_elements(interp, mro);
        INTVAL       i;

        for (i = start_at_parent; i < n; ++i) {
            PMC * const _class = VTABLE_get_pmc_keyed_int(interp, mro, i);
            PMC *ns, *methodobj;

            if (PObj_is_class_TEST(_class))
                ns = Parrot_oo_get_namespace(interp, _class);
            else
                ns = VTABLE_get_namespace(interp, _class);

            methodobj = VTABLE_get_pmc_keyed_str(interp, ns, meth);

            if (!PMC_IS_NULL(methodobj)) {
                /*
                 * mmd_is_hidden would consider all previous candidates
                 * RT #45949 pass current n so that only candidates from this
                 *     mro are used?
                 */
                if (mmd_maybe_candidate(interp, methodobj, cl))
                    break;
            }
        }
    }
}


/*

=item C<static INTVAL distance_cmp>

RT #48260: Not yet documented!!!

=cut

*/

static INTVAL
distance_cmp(SHIM_INTERP, INTVAL a, INTVAL b)
{
    short da = (short)(a & 0xffff);
    short db = (short)(b & 0xffff);

    /* sort first by distance */
    if (da > db)
        return 1;

    if (da < db)
        return -1;

    /* end then by index in candidate list */
    da = (short)(a >> 16);
    db = (short)(b >> 16);

    return da > db ? 1 : da < db ? -1 : 0;
}


/*

=item C<static PMC* mmd_cvt_to_types>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_cvt_to_types(PARROT_INTERP, ARGIN(PMC *multi_sig))
{
    PMC * const ar = pmc_new(interp, enum_class_FixedIntegerArray);
    const INTVAL n = VTABLE_elements(interp, multi_sig);
    INTVAL       i;

    VTABLE_set_integer_native(interp, ar, n);

    for (i = 0; i < n; ++i) {
        PMC * const sig_elem = VTABLE_get_pmc_keyed_int(interp, multi_sig, i);
        INTVAL type;

        if (sig_elem->vtable->base_type == enum_class_String) {
            STRING * const sig = VTABLE_get_string(interp, sig_elem);
            if (memcmp(sig->strstart, "__VOID", 6) == 0) {
                PMC_int_val(ar)--;  /* RT #45951 */
                break;
            }
            type = pmc_type(interp, sig);
        }
        else {
            type = pmc_type_p(interp, sig_elem);
        }

        VTABLE_set_integer_keyed_int(interp, ar, i, type);
    }

    return ar;
}


#define MMD_BIG_DISTANCE 0x7fff

/*

=item C<static UINTVAL mmd_distance>

Create Manhattan Distance of sub C<pmc> against given argument types.
0xffff is the maximum distance

=cut

*/

static UINTVAL
mmd_distance(PARROT_INTERP, ARGIN(PMC *pmc), ARGIN(PMC *arg_tuple))
{
    PMC *multi_sig, *mro;
    INTVAL i, n, args, dist, j, m;

    /* has to be a builtin multi method */
    if (pmc->vtable->base_type == enum_class_NCI) {
        multi_sig = PMC_pmc_val(pmc);
    }
    else if (VTABLE_isa(interp, pmc, CONST_STRING(interp, "Sub"))
         ||  VTABLE_isa(interp, pmc, CONST_STRING(interp, "Closure"))) {
        multi_sig = PMC_sub(pmc)->multi_signature;

        /* some method */
        if (!multi_sig)
            return 0;

        if (multi_sig->vtable->base_type == enum_class_FixedPMCArray) {
            multi_sig = PMC_sub(pmc)->multi_signature =
                mmd_cvt_to_types(interp, multi_sig);
        }
    }
    else
        return MMD_BIG_DISTANCE;

    n    = VTABLE_elements(interp, multi_sig);
    args = VTABLE_elements(interp, arg_tuple);

    /*
     * arg_tuple may have more arguments - only the
     * n multi_sig invocants are counted
     */
    if (args < n)
        return MMD_BIG_DISTANCE;

    dist = 0;

    if (args > n)
        dist = PARROT_MMD_MAX_CLASS_DEPTH;

    /* now go through args */
    for (i = 0; i < n; ++i) {
        const INTVAL type_sig  = VTABLE_get_integer_keyed_int(interp, multi_sig, i);
        const INTVAL type_call = VTABLE_get_integer_keyed_int(interp, arg_tuple, i);
        if (type_sig == type_call)
            continue;

        /*
         * different native types are very different, except a PMC
         * which matches any PMC
         */
        if (type_call <= 0 && type_sig == enum_type_PMC) {
            dist++;
            continue;
        }

        if ((type_sig <= 0 && type_sig != enum_type_PMC) || type_call <= 0) {
            dist = MMD_BIG_DISTANCE;
            break;
        }

        /*
         * now consider MRO of types the signature type has to be somewhere
         * in the MRO of the type_call
         */
        mro = interp->vtables[type_call]->mro;
        m   = VTABLE_elements(interp, mro);

        for (j = 0; j < m; ++j) {
            PMC * const cl = VTABLE_get_pmc_keyed_int(interp, mro, j);

            if (cl->vtable->base_type == type_sig)
                break;
            if (VTABLE_type(interp, cl) == type_sig)
                break;

            ++dist;
        }

        /*
         * if the type wasn't in MRO check, if any PMC matches
         * in that case use the distance + 1 (of an any PMC parent)
         */
        if (j == m && type_sig != enum_type_PMC) {
            dist = MMD_BIG_DISTANCE;
            break;
        }

        ++dist;
#if MMD_DEBUG
        {
            STRING *s1, *s2;
            if (type_sig < 0)
                s1 = Parrot_get_datatype_name(interp, type_sig);
            else {
                s1 = interp->vtables[type_sig]->whoami;
            }
            if (type_call < 0)
                s2 = Parrot_get_datatype_name(interp, type_call);
            else {
                s2 = interp->vtables[type_call]->whoami;
            }
            PIO_eprintf(interp, "arg %d: dist %d sig %Ss arg %Ss\n",
                i, dist, s1, s2);
        }
#endif
    }

    return dist;
}


/*

=item C<static void mmd_sort_candidates>

Sort the candidate list C<cl> by Manhattan Distance

=cut

*/

static void
mmd_sort_candidates(PARROT_INTERP, ARGIN(PMC *arg_tuple), ARGIN(PMC *cl))
{
    INTVAL  i;
    PMC    *nci;
    INTVAL *helper;
    PMC   **data;

    const INTVAL n    = VTABLE_elements(interp, cl);
    PMC * const  sort = pmc_new(interp, enum_class_FixedIntegerArray);

    /*
     * create a helper structure:
     * bits 0..15  = distance
     * bits 16..31 = idx in candidate list
     *
     * RT #45955 use half of available INTVAL bits
     */

    VTABLE_set_integer_native(interp, sort, n);
    helper = (INTVAL *)PMC_data(sort);

    for (i = 0; i < n; ++i) {
        PMC * const  pmc = VTABLE_get_pmc_keyed_int(interp, cl, i);
        const INTVAL d   = mmd_distance(interp, pmc, arg_tuple);
        helper[i]        = i << 16 | (d & 0xffff);
    }

    /* need an NCI function pointer */
    nci                 = pmc_new(interp, enum_class_NCI);
    PMC_struct_val(nci) = F2DPTR(distance_cmp);

    /* sort it */
    Parrot_quicksort(interp, (void **)helper, n, nci);

    /*
     * now helper has a sorted list of indices in the upper 16 bits
     * fill helper with sorted candidates
     */
    data = (PMC **)PMC_data(cl);

    for (i = 0; i < n; ++i) {
        const INTVAL idx = helper[i] >> 16;

        /* if the distance is big stop */
        if ((helper[i] & 0xffff) == MMD_BIG_DISTANCE) {
            PMC_int_val(cl) = i;
            break;
        }

        helper[i] = (INTVAL)data[idx];
    }

    /* use helper structure */
    PMC_data(cl)   = helper;
    PMC_data(sort) = data;
}


/*

=item C<static PMC* mmd_search_scopes>

Search all scopes for MMD candidates matching the arguments given in
C<arg_tuple>.

=cut

*/

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_search_scopes(PARROT_INTERP, ARGIN(STRING *meth))
{
    PMC * const candidates = pmc_new(interp, enum_class_ResizablePMCArray);

    const int stop         = mmd_search_cur_namespace(interp, meth, candidates);

    if (!stop)
        mmd_search_builtin(interp, meth, candidates);

    return candidates;
}


/*

=item C<static int mmd_is_hidden>

Check if the given multi sub is hidden by any inner multi sub (already in
the candidate list C<cl>.

=cut

*/

PARROT_WARN_UNUSED_RESULT
static int
mmd_is_hidden(PARROT_INTERP, ARGIN(PMC *multi), ARGIN(PMC *cl))
{
    /*
     * if the candidate list already has the a sub with the same
     * signature (long name), the outer multi is hidden
     *
     * RT #45957
     */
    UNUSED(interp);
    UNUSED(multi);
    UNUSED(cl);
    return 0;
}


/*

=item C<static int mmd_maybe_candidate>

If the candidate C<pmc> is a Sub PMC, push it on the candidate list and
return TRUE to stop further search.

If the candidate is a MultiSub remember all matching Subs and return FALSE
to continue searching outer scopes.

=cut

*/

static int
mmd_maybe_candidate(PARROT_INTERP, ARGIN(PMC *pmc), ARGIN(PMC *cl))
{
    INTVAL i, n;

    STRING * const _sub       = CONST_STRING(interp, "Sub");
    STRING * const _multi_sub = CONST_STRING(interp, "MultiSub");

    if (VTABLE_isa(interp, pmc, _sub)) {
        /* a plain sub stops outer searches */
        /* RT #45959 check arity of sub */

        VTABLE_push_pmc(interp, cl, pmc);
        return 1;
    }

    /* not a Sub or MultiSub - ignore */
    if (!VTABLE_isa(interp, pmc, _multi_sub))
        return 0;

    /* ok we have a multi sub pmc, which is an array of candidates */
    n = VTABLE_elements(interp, pmc);

    for (i = 0; i < n; ++i) {
        PMC * const multi_sub = VTABLE_get_pmc_keyed_int(interp, pmc, i);

        if (!mmd_is_hidden(interp, multi_sub, cl))
            VTABLE_push_pmc(interp, cl, multi_sub);
    }

    return 0;
}


/*

=item C<static int mmd_search_cur_namespace>

Search the current package namespace for matching candidates. Return
TRUE if the MMD search should stop.

=cut

*/

static int
mmd_search_cur_namespace(PARROT_INTERP, ARGIN(STRING *meth), ARGIN(PMC *cl))
{
    PMC * const pmc = Parrot_find_global_cur(interp, meth);

    return pmc && mmd_maybe_candidate(interp, pmc, cl);
}


/*

=item C<static PMC* mmd_get_ns>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_get_ns(PARROT_INTERP)
{
    STRING * const ns_name = CONST_STRING(interp, "__parrot_core");
    return Parrot_get_namespace_keyed_str(interp, interp->root_namespace,
                                          ns_name);
}


/*

=item C<static PMC* mmd_make_ns>

RT #48260: Not yet documented!!!

=cut

*/

PARROT_CANNOT_RETURN_NULL
PARROT_WARN_UNUSED_RESULT
static PMC*
mmd_make_ns(PARROT_INTERP)
{
    STRING * const ns_name = CONST_STRING(interp, "__parrot_core");
    return Parrot_make_namespace_keyed_str(interp, interp->root_namespace,
                                           ns_name);
}


/*

=item C<static void mmd_search_builtin>

Search the builtin namespace for matching candidates. This is the last
search in all the namespaces.

=cut

*/

static void
mmd_search_builtin(PARROT_INTERP, ARGIN(STRING *meth), ARGIN(PMC *cl))
{
    PMC * const ns  = mmd_get_ns(interp);
    PMC * const pmc = Parrot_find_global_n(interp, ns, meth);

    if (pmc)
        mmd_maybe_candidate(interp, pmc, cl);
}


/*

=item C<void mmd_create_builtin_multi_stub>

RT #48260: Not yet documented!!!

=cut

*/

void
mmd_create_builtin_multi_stub(PARROT_INTERP, ARGIN(PMC *ns), INTVAL func_nr)
{
    const char * name    = Parrot_MMD_method_name(interp, func_nr);

    /* create in constant pool */
    STRING     * const s = const_string(interp, name);
    PMC        * multi   = constant_pmc_new(interp, enum_class_MultiSub);

    VTABLE_set_pmc_keyed_str(interp, ns, s, multi);
}


/*

=item C<static void mmd_create_builtin_multi_meth_2>

RT #48260: Not yet documented!!!

=cut

*/

static void
mmd_create_builtin_multi_meth_2(PARROT_INTERP, ARGIN(PMC *ns),
        INTVAL func_nr, INTVAL type, INTVAL right, funcptr_t func_ptr)
{
    const char *short_name;
    char signature[6], val_sig;
    STRING *meth_name;
    PMC *method, *multi, *_class, *multi_sig;

    PARROT_ASSERT(type != enum_class_Null
               && type != enum_class_delegate
               && type != enum_class_Ref
               && type != enum_class_SharedRef
               && type != enum_class_deleg_pmc
               && type != enum_class_Class
               && type != enum_class_Object);

    short_name = Parrot_MMD_method_name(interp, func_nr);

    /* _int, _float, _str are just native variants of the base multi */
    val_sig = 'P';

    if (right == enum_type_INTVAL)
        val_sig = 'I';
    else if (right == enum_type_STRING)
        val_sig = 'S';
    else if (right == enum_type_FLOATVAL)
        val_sig = 'N';

    /* create NCI method in left class */
    strcpy(signature, "PJP.P");
    signature[3] = val_sig;

    if (func_nr >= MMD_EQ && func_nr <= MMD_STRCMP) {
        signature[0] = 'I';
        signature[4] = '\0';
    }

    /* implace infix like __i_add don't return a result */
    if (memcmp(short_name, "__i_", 4) == 0)
        signature[0] = 'v';

    meth_name = const_string(interp, short_name);
    _class    = interp->vtables[type]->pmc_class;
    method    = Parrot_find_method_direct(interp, _class, meth_name);

    if (PMC_IS_NULL(method)) {
        /* first method */
        method = constant_pmc_new(interp, enum_class_NCI);
        VTABLE_set_pointer_keyed_str(interp, method,
                const_string(interp, signature),
                F2DPTR(func_ptr));
        VTABLE_add_method(interp, _class, meth_name, method);
    }
    else {
        /* multiple methods with that same name */
        if (method->vtable->base_type == enum_class_NCI) {
            /* convert first to a multi */
            multi = constant_pmc_new(interp, enum_class_MultiSub);
            VTABLE_add_method(interp, _class, meth_name, multi);
            VTABLE_push_pmc(interp, multi, method);
        }
        else {
            PARROT_ASSERT(method->vtable->base_type == enum_class_MultiSub);
            multi = method;
        }
        method = constant_pmc_new(interp, enum_class_NCI);
        VTABLE_set_pointer_keyed_str(interp, method,
                const_string(interp, signature),
                F2DPTR(func_ptr));
        VTABLE_push_pmc(interp, multi, method);
    }

    /* mark MMD */
    PObj_get_FLAGS(method) |= PObj_private0_FLAG;

    /* attach the multi_signature array to PMC_pmc_val */
    multi_sig = constant_pmc_new(interp, enum_class_FixedIntegerArray);

    VTABLE_set_integer_native(interp,    multi_sig, 2);
    VTABLE_set_integer_keyed_int(interp, multi_sig, 0, type);
    VTABLE_set_integer_keyed_int(interp, multi_sig, 1, right);

    PMC_pmc_val(method) = multi_sig;

    /*
     * push method onto core multi_sub
     * RT #45961 cache the namespace
     */
    multi = Parrot_find_global_n(interp, ns, meth_name);
    PARROT_ASSERT(multi);
    VTABLE_push_pmc(interp, multi, method);
}


/*

=item C<static void mmd_create_builtin_multi_meth>

RT #48260: Not yet documented!!!

=cut

*/

static void
mmd_create_builtin_multi_meth(PARROT_INTERP, ARGIN(PMC *ns), INTVAL type,
        ARGIN(const MMD_init *entry))
{
    mmd_create_builtin_multi_meth_2(interp, ns,
            entry->func_nr, type, entry->right, entry->func_ptr);
}


/*

=item C<void Parrot_mmd_register_table>

Register MMD functions for this PMC type.

=cut

*/

PARROT_API
void
Parrot_mmd_register_table(PARROT_INTERP, INTVAL type,
        ARGIN(const MMD_init *mmd_table), INTVAL n)
{
    MMD_table * const table = interp->binop_mmd_funcs;
    PMC       * const ns    = mmd_make_ns(interp);
    INTVAL            i;

    if ((INTVAL)table->x < type && type < enum_class_core_max) {

        /* pre-allocate the function table */
        for (i = MMD_USER_FIRST - 1; i >= 0; i--) {
            mmd_register(interp, i, enum_class_core_max - 1,
                    enum_class_core_max - 1, NULL);

            /* create a MultiSub stub */
            mmd_create_builtin_multi_stub(interp, ns, i);
        }
    }

    /* register default mmds for this type */
    for (i = 0; i < n; ++i) {
#ifdef PARROT_HAS_ALIGNED_FUNCPTR
        PARROT_ASSERT((PTR2UINTVAL(mmd_table[i].func_ptr) & 3) == 0);
#endif
        mmd_register(interp,
                mmd_table[i].func_nr, type,
                mmd_table[i].right, mmd_table[i].func_ptr);
        mmd_create_builtin_multi_meth(interp, ns, type, mmd_table + i);
    }
}


/*

=item C<void Parrot_mmd_rebuild_table>

Rebuild the static MMD_table for the given class type and MMD function
number. If C<type> is negative all classes are rebuilt. If C<func_nr> is
negative all MMD functions are rebuilt.

=cut

*/

PARROT_API
void
Parrot_mmd_rebuild_table(PARROT_INTERP, INTVAL type, INTVAL func_nr)
{
    MMD_table *table;
    UINTVAL    i;

    UNUSED(type);

    if (!interp->binop_mmd_funcs)
        return;

    table = interp->binop_mmd_funcs + func_nr;

    if (!table)
        return;

    /* RT #45963 specific parts of table
     * the type and it's mro and
     * all classes that inherit from type
     */
    for (i = 0; i < table->x * table->y; ++i)
        table->mmd_funcs[i] = NULL;
}


/*

=back

=head1 SEE ALSO

F<include/parrot/mmd.h>,
F<http://svn.perl.org/perl6/doc/trunk/design/apo/A12.pod>,
F<http://svn.perl.org/perl6/doc/trunk/design/syn/S12.pod>

=cut

*/


/*
 * Local variables:
 *   c-file-style: "parrot"
 * End:
 * vim: expandtab shiftwidth=4:
 */