update libressl to 2.8.2

[unleashed.git] / lib / libcrypto / bn / bn_lib.c

/* $OpenBSD: bn_lib.c,v 1.45 2018/07/23 18:14:32 tb Exp $ */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#ifndef BN_DEBUG
# undef NDEBUG /* avoid conflicting definitions */
# define NDEBUG
#endif

#include <assert.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>

#include <openssl/opensslconf.h>

#include <openssl/err.h>

#include "bn_lcl.h"

/* This stuff appears to be completely unused, so is deprecated */
#ifndef OPENSSL_NO_DEPRECATED
/* For a 32 bit machine
 * 2 -   4 ==  128
 * 3 -   8 ==  256
 * 4 -  16 ==  512
 * 5 -  32 == 1024
 * 6 -  64 == 2048
 * 7 - 128 == 4096
 * 8 - 256 == 8192
 */
static int bn_limit_bits = 0;
static int bn_limit_num = 8;        /* (1<<bn_limit_bits) */
static int bn_limit_bits_low = 0;
static int bn_limit_num_low = 8;    /* (1<<bn_limit_bits_low) */
static int bn_limit_bits_high = 0;
static int bn_limit_num_high = 8;   /* (1<<bn_limit_bits_high) */
static int bn_limit_bits_mont = 0;
static int bn_limit_num_mont = 8;   /* (1<<bn_limit_bits_mont) */

void
BN_set_params(int mult, int high, int low, int mont)
{
        if (mult >= 0) {
                if (mult > (int)(sizeof(int) * 8) - 1)
                        mult = sizeof(int) * 8 - 1;
                bn_limit_bits = mult;
                bn_limit_num = 1 << mult;
        }
        if (high >= 0) {
                if (high > (int)(sizeof(int) * 8) - 1)
                        high = sizeof(int) * 8 - 1;
                bn_limit_bits_high = high;
                bn_limit_num_high = 1 << high;
        }
        if (low >= 0) {
                if (low > (int)(sizeof(int) * 8) - 1)
                        low = sizeof(int) * 8 - 1;
                bn_limit_bits_low = low;
                bn_limit_num_low = 1 << low;
        }
        if (mont >= 0) {
                if (mont > (int)(sizeof(int) * 8) - 1)
                        mont = sizeof(int) * 8 - 1;
                bn_limit_bits_mont = mont;
                bn_limit_num_mont = 1 << mont;
        }
}

int
BN_get_params(int which)
{
        if (which == 0)
                return (bn_limit_bits);
        else if (which == 1)
                return (bn_limit_bits_high);
        else if (which == 2)
                return (bn_limit_bits_low);
        else if (which == 3)
                return (bn_limit_bits_mont);
        else
                return (0);
}
#endif

const BIGNUM *
BN_value_one(void)
{
        static const BN_ULONG data_one = 1L;
        static const BIGNUM const_one = {
                (BN_ULONG *)&data_one, 1, 1, 0, BN_FLG_STATIC_DATA
        };

        return (&const_one);
}

int
BN_num_bits_word(BN_ULONG l)
{
        static const unsigned char bits[256] = {
                0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
                5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
                6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
                6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
                7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
                7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
                7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
                7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,  8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
                8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        };

#ifdef _LP64
        if (l & 0xffffffff00000000L) {
                if (l & 0xffff000000000000L) {
                        if (l & 0xff00000000000000L) {
                                return (bits[(int)(l >> 56)] + 56);
                        } else
                                return (bits[(int)(l >> 48)] + 48);
                } else {
                        if (l & 0x0000ff0000000000L) {
                                return (bits[(int)(l >> 40)] + 40);
                        } else
                                return (bits[(int)(l >> 32)] + 32);
                }
        } else
#endif
        {
                if (l & 0xffff0000L) {
                        if (l & 0xff000000L)
                                return (bits[(int)(l >> 24L)] + 24);
                        else
                                return (bits[(int)(l >> 16L)] + 16);
                } else {
                        if (l & 0xff00L)
                                return (bits[(int)(l >> 8)] + 8);
                        else
                                return (bits[(int)(l)]);
                }
        }
}

int
BN_num_bits(const BIGNUM *a)
{
        int i = a->top - 1;

        bn_check_top(a);

        if (BN_is_zero(a))
                return 0;
        return ((i * BN_BITS2) + BN_num_bits_word(a->d[i]));
}

void
BN_clear_free(BIGNUM *a)
{
        int i;

        if (a == NULL)
                return;
        bn_check_top(a);
        if (a->d != NULL && !(BN_get_flags(a, BN_FLG_STATIC_DATA)))
                freezero(a->d, a->dmax * sizeof(a->d[0]));
        i = BN_get_flags(a, BN_FLG_MALLOCED);
        explicit_bzero(a, sizeof(BIGNUM));
        if (i)
                free(a);
}

void
BN_free(BIGNUM *a)
{
        BN_clear_free(a);
}

void
BN_init(BIGNUM *a)
{
        memset(a, 0, sizeof(BIGNUM));
        bn_check_top(a);
}

BIGNUM *
BN_new(void)
{
        BIGNUM *ret;

        if ((ret = malloc(sizeof(BIGNUM))) == NULL) {
                BNerror(ERR_R_MALLOC_FAILURE);
                return (NULL);
        }
        ret->flags = BN_FLG_MALLOCED;
        ret->top = 0;
        ret->neg = 0;
        ret->dmax = 0;
        ret->d = NULL;
        bn_check_top(ret);
        return (ret);
}

/* This is used both by bn_expand2() and bn_dup_expand() */
/* The caller MUST check that words > b->dmax before calling this */
static BN_ULONG *
bn_expand_internal(const BIGNUM *b, int words)
{
        BN_ULONG *A, *a = NULL;
        const BN_ULONG *B;
        int i;

        bn_check_top(b);

        if (words > (INT_MAX/(4*BN_BITS2))) {
                BNerror(BN_R_BIGNUM_TOO_LONG);
                return NULL;
        }
        if (BN_get_flags(b, BN_FLG_STATIC_DATA)) {
                BNerror(BN_R_EXPAND_ON_STATIC_BIGNUM_DATA);
                return (NULL);
        }
        a = A = reallocarray(NULL, words, sizeof(BN_ULONG));
        if (A == NULL) {
                BNerror(ERR_R_MALLOC_FAILURE);
                return (NULL);
        }
#if 1
        B = b->d;
        /* Check if the previous number needs to be copied */
        if (B != NULL) {
                for (i = b->top >> 2; i > 0; i--, A += 4, B += 4) {
                        /*
                         * The fact that the loop is unrolled
                         * 4-wise is a tribute to Intel. It's
                         * the one that doesn't have enough
                         * registers to accommodate more data.
                         * I'd unroll it 8-wise otherwise:-)
                         *
                         *              <appro@fy.chalmers.se>
                         */
                        BN_ULONG a0, a1, a2, a3;
                        a0 = B[0];
                        a1 = B[1];
                        a2 = B[2];
                        a3 = B[3];
                        A[0] = a0;
                        A[1] = a1;
                        A[2] = a2;
                        A[3] = a3;
                }
                switch (b->top & 3) {
                case 3:
                        A[2] = B[2];
                case 2:
                        A[1] = B[1];
                case 1:
                        A[0] = B[0];
                }
        }

#else
        memset(A, 0, sizeof(BN_ULONG) * words);
        memcpy(A, b->d, sizeof(b->d[0]) * b->top);
#endif

        return (a);
}

/* This is an internal function that can be used instead of bn_expand2()
 * when there is a need to copy BIGNUMs instead of only expanding the
 * data part, while still expanding them.
 * Especially useful when needing to expand BIGNUMs that are declared
 * 'const' and should therefore not be changed.
 * The reason to use this instead of a BN_dup() followed by a bn_expand2()
 * is memory allocation overhead.  A BN_dup() followed by a bn_expand2()
 * will allocate new memory for the BIGNUM data twice, and free it once,
 * while bn_dup_expand() makes sure allocation is made only once.
 */

#ifndef OPENSSL_NO_DEPRECATED
BIGNUM *
bn_dup_expand(const BIGNUM *b, int words)
{
        BIGNUM *r = NULL;

        bn_check_top(b);

        /* This function does not work if
         *      words <= b->dmax && top < words
         * because BN_dup() does not preserve 'dmax'!
         * (But bn_dup_expand() is not used anywhere yet.)
         */

        if (words > b->dmax) {
                BN_ULONG *a = bn_expand_internal(b, words);

                if (a) {
                        r = BN_new();
                        if (r) {
                                r->top = b->top;
                                r->dmax = words;
                                r->neg = b->neg;
                                r->d = a;
                        } else {
                                /* r == NULL, BN_new failure */
                                free(a);
                        }
                }
                /* If a == NULL, there was an error in allocation in
                   bn_expand_internal(), and NULL should be returned */
        } else {
                r = BN_dup(b);
        }

        bn_check_top(r);
        return r;
}
#endif

/* This is an internal function that should not be used in applications.
 * It ensures that 'b' has enough room for a 'words' word number
 * and initialises any unused part of b->d with leading zeros.
 * It is mostly used by the various BIGNUM routines. If there is an error,
 * NULL is returned. If not, 'b' is returned. */

BIGNUM *
bn_expand2(BIGNUM *b, int words)
{
        bn_check_top(b);

        if (words > b->dmax) {
                BN_ULONG *a = bn_expand_internal(b, words);
                if (!a)
                        return NULL;
                if (b->d)
                        freezero(b->d, b->dmax * sizeof(b->d[0]));
                b->d = a;
                b->dmax = words;
        }

/* None of this should be necessary because of what b->top means! */
#if 0
        /* NB: bn_wexpand() calls this only if the BIGNUM really has to grow */
        if (b->top < b->dmax) {
                int i;
                BN_ULONG *A = &(b->d[b->top]);
                for (i = (b->dmax - b->top) >> 3; i > 0; i--, A += 8) {
                        A[0] = 0;
                        A[1] = 0;
                        A[2] = 0;
                        A[3] = 0;
                        A[4] = 0;
                        A[5] = 0;
                        A[6] = 0;
                        A[7] = 0;
                }
                for (i = (b->dmax - b->top)&7; i > 0; i--, A++)
                        A[0] = 0;
                assert(A == &(b->d[b->dmax]));
        }
#endif
        bn_check_top(b);
        return b;
}

BIGNUM *
BN_dup(const BIGNUM *a)
{
        BIGNUM *t;

        if (a == NULL)
                return NULL;
        bn_check_top(a);

        t = BN_new();
        if (t == NULL)
                return NULL;
        if (!BN_copy(t, a)) {
                BN_free(t);
                return NULL;
        }
        bn_check_top(t);
        return t;
}

BIGNUM *
BN_copy(BIGNUM *a, const BIGNUM *b)
{
        int i;
        BN_ULONG *A;
        const BN_ULONG *B;

        bn_check_top(b);

        if (a == b)
                return (a);
        if (bn_wexpand(a, b->top) == NULL)
                return (NULL);

#if 1
        A = a->d;
        B = b->d;
        for (i = b->top >> 2; i > 0; i--, A += 4, B += 4) {
                BN_ULONG a0, a1, a2, a3;
                a0 = B[0];
                a1 = B[1];
                a2 = B[2];
                a3 = B[3];
                A[0] = a0;
                A[1] = a1;
                A[2] = a2;
                A[3] = a3;
        }
        switch (b->top & 3) {
        case 3:
                A[2] = B[2];
        case 2:
                A[1] = B[1];
        case 1:
                A[0] = B[0];
        }
#else
        memcpy(a->d, b->d, sizeof(b->d[0]) * b->top);
#endif

        a->top = b->top;
        a->neg = b->neg;
        bn_check_top(a);
        return (a);
}

void
BN_swap(BIGNUM *a, BIGNUM *b)
{
        int flags_old_a, flags_old_b;
        BN_ULONG *tmp_d;
        int tmp_top, tmp_dmax, tmp_neg;

        bn_check_top(a);
        bn_check_top(b);

        flags_old_a = a->flags;
        flags_old_b = b->flags;

        tmp_d = a->d;
        tmp_top = a->top;
        tmp_dmax = a->dmax;
        tmp_neg = a->neg;

        a->d = b->d;
        a->top = b->top;
        a->dmax = b->dmax;
        a->neg = b->neg;

        b->d = tmp_d;
        b->top = tmp_top;
        b->dmax = tmp_dmax;
        b->neg = tmp_neg;

        a->flags = (flags_old_a & BN_FLG_MALLOCED) |
            (flags_old_b & BN_FLG_STATIC_DATA);
        b->flags = (flags_old_b & BN_FLG_MALLOCED) |
            (flags_old_a & BN_FLG_STATIC_DATA);
        bn_check_top(a);
        bn_check_top(b);
}

void
BN_clear(BIGNUM *a)
{
        bn_check_top(a);
        if (a->d != NULL)
                explicit_bzero(a->d, a->dmax * sizeof(a->d[0]));
        a->top = 0;
        a->neg = 0;
}

BN_ULONG
BN_get_word(const BIGNUM *a)
{
        if (a->top > 1)
                return BN_MASK2;
        else if (a->top == 1)
                return a->d[0];
        /* a->top == 0 */
        return 0;
}

BIGNUM *
bn_expand(BIGNUM *a, int bits)
{
        if (bits > (INT_MAX - BN_BITS2 + 1))
                return (NULL);

        if (((bits + BN_BITS2 - 1) / BN_BITS2) <= a->dmax)
                return (a);

        return bn_expand2(a, (bits + BN_BITS2 - 1) / BN_BITS2);
}

int
BN_set_word(BIGNUM *a, BN_ULONG w)
{
        bn_check_top(a);
        if (bn_expand(a, (int)sizeof(BN_ULONG) * 8) == NULL)
                return (0);
        a->neg = 0;
        a->d[0] = w;
        a->top = (w ? 1 : 0);
        bn_check_top(a);
        return (1);
}

BIGNUM *
BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
{
        unsigned int i, m;
        unsigned int n;
        BN_ULONG l;
        BIGNUM *bn = NULL;

        if (ret == NULL)
                ret = bn = BN_new();
        if (ret == NULL)
                return (NULL);
        bn_check_top(ret);
        l = 0;
        n = len;
        if (n == 0) {
                ret->top = 0;
                return (ret);
        }
        i = ((n - 1) / BN_BYTES) + 1;
        m = ((n - 1) % (BN_BYTES));
        if (bn_wexpand(ret, (int)i) == NULL) {
                BN_free(bn);
                return NULL;
        }
        ret->top = i;
        ret->neg = 0;
        while (n--) {
                l = (l << 8L) | *(s++);
                if (m-- == 0) {
                        ret->d[--i] = l;
                        l = 0;
                        m = BN_BYTES - 1;
                }
        }
        /* need to call this due to clear byte at top if avoiding
         * having the top bit set (-ve number) */
        bn_correct_top(ret);
        return (ret);
}

/* ignore negative */
int
BN_bn2bin(const BIGNUM *a, unsigned char *to)
{
        int n, i;
        BN_ULONG l;

        bn_check_top(a);
        n = i=BN_num_bytes(a);
        while (i--) {
                l = a->d[i / BN_BYTES];
                *(to++) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
        }
        return (n);
}

int
BN_ucmp(const BIGNUM *a, const BIGNUM *b)
{
        int i;
        BN_ULONG t1, t2, *ap, *bp;

        bn_check_top(a);
        bn_check_top(b);

        i = a->top - b->top;
        if (i != 0)
                return (i);
        ap = a->d;
        bp = b->d;
        for (i = a->top - 1; i >= 0; i--) {
                t1 = ap[i];
                t2 = bp[i];
                if (t1 != t2)
                        return ((t1 > t2) ? 1 : -1);
        }
        return (0);
}

int
BN_cmp(const BIGNUM *a, const BIGNUM *b)
{
        int i;
        int gt, lt;
        BN_ULONG t1, t2;

        if ((a == NULL) || (b == NULL)) {
                if (a != NULL)
                        return (-1);
                else if (b != NULL)
                        return (1);
                else
                        return (0);
        }

        bn_check_top(a);
        bn_check_top(b);

        if (a->neg != b->neg) {
                if (a->neg)
                        return (-1);
                else
                        return (1);
        }
        if (a->neg == 0) {
                gt = 1;
                lt = -1;
        } else {
                gt = -1;
                lt = 1;
        }

        if (a->top > b->top)
                return (gt);
        if (a->top < b->top)
                return (lt);
        for (i = a->top - 1; i >= 0; i--) {
                t1 = a->d[i];
                t2 = b->d[i];
                if (t1 > t2)
                        return (gt);
                if (t1 < t2)
                        return (lt);
        }
        return (0);
}

int
BN_set_bit(BIGNUM *a, int n)
{
        int i, j, k;

        if (n < 0)
                return 0;

        i = n / BN_BITS2;
        j = n % BN_BITS2;
        if (a->top <= i) {
                if (bn_wexpand(a, i + 1) == NULL)
                        return (0);
                for (k = a->top; k < i + 1; k++)
                        a->d[k] = 0;
                a->top = i + 1;
        }

        a->d[i] |= (((BN_ULONG)1) << j);
        bn_check_top(a);
        return (1);
}

int
BN_clear_bit(BIGNUM *a, int n)
{
        int i, j;

        bn_check_top(a);
        if (n < 0)
                return 0;

        i = n / BN_BITS2;
        j = n % BN_BITS2;
        if (a->top <= i)
                return (0);

        a->d[i] &= (~(((BN_ULONG)1) << j));
        bn_correct_top(a);
        return (1);
}

int
BN_is_bit_set(const BIGNUM *a, int n)
{
        int i, j;

        bn_check_top(a);
        if (n < 0)
                return 0;
        i = n / BN_BITS2;
        j = n % BN_BITS2;
        if (a->top <= i)
                return 0;
        return (int)(((a->d[i]) >> j) & ((BN_ULONG)1));
}

int
BN_mask_bits(BIGNUM *a, int n)
{
        int b, w;

        bn_check_top(a);
        if (n < 0)
                return 0;

        w = n / BN_BITS2;
        b = n % BN_BITS2;
        if (w >= a->top)
                return 0;
        if (b == 0)
                a->top = w;
        else {
                a->top = w + 1;
                a->d[w] &= ~(BN_MASK2 << b);
        }
        bn_correct_top(a);
        return (1);
}

void
BN_set_negative(BIGNUM *a, int b)
{
        if (b && !BN_is_zero(a))
                a->neg = 1;
        else
                a->neg = 0;
}

int
bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n)
{
        int i;
        BN_ULONG aa, bb;

        aa = a[n - 1];
        bb = b[n - 1];
        if (aa != bb)
                return ((aa > bb) ? 1 : -1);
        for (i = n - 2; i >= 0; i--) {
                aa = a[i];
                bb = b[i];
                if (aa != bb)
                        return ((aa > bb) ? 1 : -1);
        }
        return (0);
}

/* Here follows a specialised variants of bn_cmp_words().  It has the
   property of performing the operation on arrays of different sizes.
   The sizes of those arrays is expressed through cl, which is the
   common length ( basicall, min(len(a),len(b)) ), and dl, which is the
   delta between the two lengths, calculated as len(a)-len(b).
   All lengths are the number of BN_ULONGs...  */

int
bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b, int cl, int dl)
{
        int n, i;

        n = cl - 1;

        if (dl < 0) {
                for (i = dl; i < 0; i++) {
                        if (b[n - i] != 0)
                                return -1; /* a < b */
                }
        }
        if (dl > 0) {
                for (i = dl; i > 0; i--) {
                        if (a[n + i] != 0)
                                return 1; /* a > b */
                }
        }
        return bn_cmp_words(a, b, cl);
}

/*
 * Constant-time conditional swap of a and b.
 * a and b are swapped if condition is not 0.
 * The code assumes that at most one bit of condition is set.
 * nwords is the number of words to swap.
 * The code assumes that at least nwords are allocated in both a and b,
 * and that no more than nwords are used by either a or b.
 * a and b cannot be the same number
 */
void
BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
{
        BN_ULONG t;
        int i;

        bn_wcheck_size(a, nwords);
        bn_wcheck_size(b, nwords);

        assert(a != b);
        assert((condition & (condition - 1)) == 0);
        assert(sizeof(BN_ULONG) >= sizeof(int));

        condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;

        t = (a->top^b->top) & condition;
        a->top ^= t;
        b->top ^= t;

#define BN_CONSTTIME_SWAP(ind) \
        do { \
                t = (a->d[ind] ^ b->d[ind]) & condition; \
                a->d[ind] ^= t; \
                b->d[ind] ^= t; \
        } while (0)


        switch (nwords) {
        default:
                for (i = 10; i < nwords; i++)
                        BN_CONSTTIME_SWAP(i);
                /* Fallthrough */
        case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */
        case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */
        case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */
        case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */
        case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */
        case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */
        case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */
        case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */
        case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */
        case 1:
                BN_CONSTTIME_SWAP(0);
        }
#undef BN_CONSTTIME_SWAP
}

/*
 * Constant-time conditional swap of a and b.
 * a and b are swapped if condition is not 0.
 * nwords is the number of words to swap.
 */
int
BN_swap_ct(BN_ULONG condition, BIGNUM *a, BIGNUM *b, size_t nwords)
{
        BN_ULONG t;
        int i, words;

        if (a == b)
                return 1;
        if (nwords > INT_MAX)
                return 0;
        words = (int)nwords;
        if (bn_wexpand(a, words) == NULL || bn_wexpand(b, words) == NULL)
                return 0;
        if (a->top > words || b->top > words) {
                BNerror(BN_R_INVALID_LENGTH);
                return 0;
        }

        /* Set condition to 0 (if it was zero) or all 1s otherwise. */
        condition = ((~condition & (condition - 1)) >> (BN_BITS2 - 1)) - 1;

        /* swap top field */
        t = (a->top ^ b->top) & condition;
        a->top ^= t;
        b->top ^= t;

        /* swap neg field */
        t = (a->neg ^ b->neg) & condition;
        a->neg ^= t;
        b->neg ^= t;

        /* swap BN_FLG_CONSTTIME from flag field */
        t = ((a->flags ^ b->flags) & BN_FLG_CONSTTIME) & condition;
        a->flags ^= t;
        b->flags ^= t;

        /* swap the data */
        for (i = 0; i < words; i++) {
                t = (a->d[i] ^ b->d[i]) & condition;
                a->d[i] ^= t;
                b->d[i] ^= t;
        }

        return 1;
}

BN_GENCB *
BN_GENCB_new(void)
{
        BN_GENCB *cb;

        if ((cb = calloc(1, sizeof(*cb))) == NULL)
                return NULL;

        return cb;
}

void
BN_GENCB_free(BN_GENCB *cb)
{
        if (cb == NULL)
                return;
        free(cb);
}

void *
BN_GENCB_get_arg(BN_GENCB *cb)
{
        return cb->arg;
}