re PR lto/48086 (bootstrap-lto creates c-common.s with too many sections on x86_64...

[official-gcc.git] / libgo / go / gob / encode.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gob

import (
        "bytes"
        "io"
        "math"
        "os"
        "reflect"
        "unsafe"
)

const uint64Size = unsafe.Sizeof(uint64(0))

// The global execution state of an instance of the encoder.
// Field numbers are delta encoded and always increase. The field
// number is initialized to -1 so 0 comes out as delta(1). A delta of
// 0 terminates the structure.
type encoderState struct {
        enc      *Encoder
        b        *bytes.Buffer
        sendZero bool                 // encoding an array element or map key/value pair; send zero values
        fieldnum int                  // the last field number written.
        buf      [1 + uint64Size]byte // buffer used by the encoder; here to avoid allocation.
}

func newEncoderState(enc *Encoder, b *bytes.Buffer) *encoderState {
        return &encoderState{enc: enc, b: b}
}

// Unsigned integers have a two-state encoding.  If the number is less
// than 128 (0 through 0x7F), its value is written directly.
// Otherwise the value is written in big-endian byte order preceded
// by the byte length, negated.

// encodeUint writes an encoded unsigned integer to state.b.
func (state *encoderState) encodeUint(x uint64) {
        if x <= 0x7F {
                err := state.b.WriteByte(uint8(x))
                if err != nil {
                        error(err)
                }
                return
        }
        var n, m int
        m = uint64Size
        for n = 1; x > 0; n++ {
                state.buf[m] = uint8(x & 0xFF)
                x >>= 8
                m--
        }
        state.buf[m] = uint8(-(n - 1))
        n, err := state.b.Write(state.buf[m : uint64Size+1])
        if err != nil {
                error(err)
        }
}

// encodeInt writes an encoded signed integer to state.w.
// The low bit of the encoding says whether to bit complement the (other bits of the)
// uint to recover the int.
func (state *encoderState) encodeInt(i int64) {
        var x uint64
        if i < 0 {
                x = uint64(^i<<1) | 1
        } else {
                x = uint64(i << 1)
        }
        state.encodeUint(uint64(x))
}

type encOp func(i *encInstr, state *encoderState, p unsafe.Pointer)

// The 'instructions' of the encoding machine
type encInstr struct {
        op     encOp
        field  int     // field number
        indir  int     // how many pointer indirections to reach the value in the struct
        offset uintptr // offset in the structure of the field to encode
}

// Emit a field number and update the state to record its value for delta encoding.
// If the instruction pointer is nil, do nothing
func (state *encoderState) update(instr *encInstr) {
        if instr != nil {
                state.encodeUint(uint64(instr.field - state.fieldnum))
                state.fieldnum = instr.field
        }
}

// Each encoder is responsible for handling any indirections associated
// with the data structure.  If any pointer so reached is nil, no bytes are written.
// If the data item is zero, no bytes are written.
// Otherwise, the output (for a scalar) is the field number, as an encoded integer,
// followed by the field data in its appropriate format.

func encIndirect(p unsafe.Pointer, indir int) unsafe.Pointer {
        for ; indir > 0; indir-- {
                p = *(*unsafe.Pointer)(p)
                if p == nil {
                        return unsafe.Pointer(nil)
                }
        }
        return p
}

func encBool(i *encInstr, state *encoderState, p unsafe.Pointer) {
        b := *(*bool)(p)
        if b || state.sendZero {
                state.update(i)
                if b {
                        state.encodeUint(1)
                } else {
                        state.encodeUint(0)
                }
        }
}

func encInt(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

func encUint(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

func encInt8(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int8)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

func encUint8(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint8)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

func encInt16(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int16)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

func encUint16(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint16)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

func encInt32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int32)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

func encUint32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint32)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

func encInt64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := *(*int64)(p)
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

func encUint64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := *(*uint64)(p)
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

func encUintptr(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uintptr)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// Floating-point numbers are transmitted as uint64s holding the bits
// of the underlying representation.  They are sent byte-reversed, with
// the exponent end coming out first, so integer floating point numbers
// (for example) transmit more compactly.  This routine does the
// swizzling.
func floatBits(f float64) uint64 {
        u := math.Float64bits(f)
        var v uint64
        for i := 0; i < 8; i++ {
                v <<= 8
                v |= u & 0xFF
                u >>= 8
        }
        return v
}

func encFloat32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        f := *(*float32)(p)
        if f != 0 || state.sendZero {
                v := floatBits(float64(f))
                state.update(i)
                state.encodeUint(v)
        }
}

func encFloat64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        f := *(*float64)(p)
        if f != 0 || state.sendZero {
                state.update(i)
                v := floatBits(f)
                state.encodeUint(v)
        }
}

// Complex numbers are just a pair of floating-point numbers, real part first.
func encComplex64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        c := *(*complex64)(p)
        if c != 0+0i || state.sendZero {
                rpart := floatBits(float64(real(c)))
                ipart := floatBits(float64(imag(c)))
                state.update(i)
                state.encodeUint(rpart)
                state.encodeUint(ipart)
        }
}

func encComplex128(i *encInstr, state *encoderState, p unsafe.Pointer) {
        c := *(*complex128)(p)
        if c != 0+0i || state.sendZero {
                rpart := floatBits(real(c))
                ipart := floatBits(imag(c))
                state.update(i)
                state.encodeUint(rpart)
                state.encodeUint(ipart)
        }
}

func encNoOp(i *encInstr, state *encoderState, p unsafe.Pointer) {
}

// Byte arrays are encoded as an unsigned count followed by the raw bytes.
func encUint8Array(i *encInstr, state *encoderState, p unsafe.Pointer) {
        b := *(*[]byte)(p)
        if len(b) > 0 || state.sendZero {
                state.update(i)
                state.encodeUint(uint64(len(b)))
                state.b.Write(b)
        }
}

// Strings are encoded as an unsigned count followed by the raw bytes.
func encString(i *encInstr, state *encoderState, p unsafe.Pointer) {
        s := *(*string)(p)
        if len(s) > 0 || state.sendZero {
                state.update(i)
                state.encodeUint(uint64(len(s)))
                io.WriteString(state.b, s)
        }
}

// The end of a struct is marked by a delta field number of 0.
func encStructTerminator(i *encInstr, state *encoderState, p unsafe.Pointer) {
        state.encodeUint(0)
}

// Execution engine

// The encoder engine is an array of instructions indexed by field number of the encoding
// data, typically a struct.  It is executed top to bottom, walking the struct.
type encEngine struct {
        instr []encInstr
}

const singletonField = 0

func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintptr) {
        state := newEncoderState(enc, b)
        state.fieldnum = singletonField
        // There is no surrounding struct to frame the transmission, so we must
        // generate data even if the item is zero.  To do this, set sendZero.
        state.sendZero = true
        instr := &engine.instr[singletonField]
        p := unsafe.Pointer(basep) // offset will be zero
        if instr.indir > 0 {
                if p = encIndirect(p, instr.indir); p == nil {
                        return
                }
        }
        instr.op(instr, state, p)
}

func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintptr) {
        state := newEncoderState(enc, b)
        state.fieldnum = -1
        for i := 0; i < len(engine.instr); i++ {
                instr := &engine.instr[i]
                p := unsafe.Pointer(basep + instr.offset)
                if instr.indir > 0 {
                        if p = encIndirect(p, instr.indir); p == nil {
                                continue
                        }
                }
                instr.op(instr, state, p)
        }
}

func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, elemIndir int, length int) {
        state := newEncoderState(enc, b)
        state.fieldnum = -1
        state.sendZero = true
        state.encodeUint(uint64(length))
        for i := 0; i < length; i++ {
                elemp := p
                up := unsafe.Pointer(elemp)
                if elemIndir > 0 {
                        if up = encIndirect(up, elemIndir); up == nil {
                                errorf("gob: encodeArray: nil element")
                        }
                        elemp = uintptr(up)
                }
                op(nil, state, unsafe.Pointer(elemp))
                p += uintptr(elemWid)
        }
}

func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir int) {
        for i := 0; i < indir && v != nil; i++ {
                v = reflect.Indirect(v)
        }
        if v == nil {
                errorf("gob: encodeReflectValue: nil element")
        }
        op(nil, state, unsafe.Pointer(v.Addr()))
}

func (enc *Encoder) encodeMap(b *bytes.Buffer, mv *reflect.MapValue, keyOp, elemOp encOp, keyIndir, elemIndir int) {
        state := newEncoderState(enc, b)
        state.fieldnum = -1
        state.sendZero = true
        keys := mv.Keys()
        state.encodeUint(uint64(len(keys)))
        for _, key := range keys {
                encodeReflectValue(state, key, keyOp, keyIndir)
                encodeReflectValue(state, mv.Elem(key), elemOp, elemIndir)
        }
}

// To send an interface, we send a string identifying the concrete type, followed
// by the type identifier (which might require defining that type right now), followed
// by the concrete value.  A nil value gets sent as the empty string for the name,
// followed by no value.
func (enc *Encoder) encodeInterface(b *bytes.Buffer, iv *reflect.InterfaceValue) {
        state := newEncoderState(enc, b)
        state.fieldnum = -1
        state.sendZero = true
        if iv.IsNil() {
                state.encodeUint(0)
                return
        }

        typ, _ := indirect(iv.Elem().Type())
        name, ok := concreteTypeToName[typ]
        if !ok {
                errorf("gob: type not registered for interface: %s", typ)
        }
        // Send the name.
        state.encodeUint(uint64(len(name)))
        _, err := io.WriteString(state.b, name)
        if err != nil {
                error(err)
        }
        // Send (and maybe first define) the type id.
        enc.sendTypeDescriptor(typ)
        // Encode the value into a new buffer.
        data := new(bytes.Buffer)
        err = enc.encode(data, iv.Elem())
        if err != nil {
                error(err)
        }
        state.encodeUint(uint64(data.Len()))
        _, err = state.b.Write(data.Bytes())
        if err != nil {
                error(err)
        }
}

var encOpMap = []encOp{
        reflect.Bool:       encBool,
        reflect.Int:        encInt,
        reflect.Int8:       encInt8,
        reflect.Int16:      encInt16,
        reflect.Int32:      encInt32,
        reflect.Int64:      encInt64,
        reflect.Uint:       encUint,
        reflect.Uint8:      encUint8,
        reflect.Uint16:     encUint16,
        reflect.Uint32:     encUint32,
        reflect.Uint64:     encUint64,
        reflect.Uintptr:    encUintptr,
        reflect.Float32:    encFloat32,
        reflect.Float64:    encFloat64,
        reflect.Complex64:  encComplex64,
        reflect.Complex128: encComplex128,
        reflect.String:     encString,
}

// Return the encoding op for the base type under rt and
// the indirection count to reach it.
func (enc *Encoder) encOpFor(rt reflect.Type) (encOp, int) {
        typ, indir := indirect(rt)
        var op encOp
        k := typ.Kind()
        if int(k) < len(encOpMap) {
                op = encOpMap[k]
        }
        if op == nil {
                // Special cases
                switch t := typ.(type) {
                case *reflect.SliceType:
                        if t.Elem().Kind() == reflect.Uint8 {
                                op = encUint8Array
                                break
                        }
                        // Slices have a header; we decode it to find the underlying array.
                        elemOp, indir := enc.encOpFor(t.Elem())
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                slice := (*reflect.SliceHeader)(p)
                                if !state.sendZero && slice.Len == 0 {
                                        return
                                }
                                state.update(i)
                                state.enc.encodeArray(state.b, slice.Data, elemOp, t.Elem().Size(), indir, int(slice.Len))
                        }
                case *reflect.ArrayType:
                        // True arrays have size in the type.
                        elemOp, indir := enc.encOpFor(t.Elem())
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                state.update(i)
                                state.enc.encodeArray(state.b, uintptr(p), elemOp, t.Elem().Size(), indir, t.Len())
                        }
                case *reflect.MapType:
                        keyOp, keyIndir := enc.encOpFor(t.Key())
                        elemOp, elemIndir := enc.encOpFor(t.Elem())
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                // Maps cannot be accessed by moving addresses around the way
                                // that slices etc. can.  We must recover a full reflection value for
                                // the iteration.
                                v := reflect.NewValue(unsafe.Unreflect(t, unsafe.Pointer((p))))
                                mv := reflect.Indirect(v).(*reflect.MapValue)
                                if !state.sendZero && mv.Len() == 0 {
                                        return
                                }
                                state.update(i)
                                state.enc.encodeMap(state.b, mv, keyOp, elemOp, keyIndir, elemIndir)
                        }
                case *reflect.StructType:
                        // Generate a closure that calls out to the engine for the nested type.
                        enc.getEncEngine(typ)
                        info := mustGetTypeInfo(typ)
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                state.update(i)
                                // indirect through info to delay evaluation for recursive structs
                                state.enc.encodeStruct(state.b, info.encoder, uintptr(p))
                        }
                case *reflect.InterfaceType:
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                // Interfaces transmit the name and contents of the concrete
                                // value they contain.
                                v := reflect.NewValue(unsafe.Unreflect(t, unsafe.Pointer((p))))
                                iv := reflect.Indirect(v).(*reflect.InterfaceValue)
                                if !state.sendZero && (iv == nil || iv.IsNil()) {
                                        return
                                }
                                state.update(i)
                                state.enc.encodeInterface(state.b, iv)
                        }
                }
        }
        if op == nil {
                errorf("gob enc: can't happen: encode type %s", rt.String())
        }
        return op, indir
}

// The local Type was compiled from the actual value, so we know it's compatible.
func (enc *Encoder) compileEnc(rt reflect.Type) *encEngine {
        srt, isStruct := rt.(*reflect.StructType)
        engine := new(encEngine)
        if isStruct {
                engine.instr = make([]encInstr, srt.NumField()+1) // +1 for terminator
                for fieldnum := 0; fieldnum < srt.NumField(); fieldnum++ {
                        f := srt.Field(fieldnum)
                        op, indir := enc.encOpFor(f.Type)
                        if !isExported(f.Name) {
                                op = encNoOp
                        }
                        engine.instr[fieldnum] = encInstr{op, fieldnum, indir, uintptr(f.Offset)}
                }
                engine.instr[srt.NumField()] = encInstr{encStructTerminator, 0, 0, 0}
        } else {
                engine.instr = make([]encInstr, 1)
                op, indir := enc.encOpFor(rt)
                engine.instr[0] = encInstr{op, singletonField, indir, 0} // offset is zero
        }
        return engine
}

// typeLock must be held (or we're in initialization and guaranteed single-threaded).
// The reflection type must have all its indirections processed out.
func (enc *Encoder) getEncEngine(rt reflect.Type) *encEngine {
        info, err1 := getTypeInfo(rt)
        if err1 != nil {
                error(err1)
        }
        if info.encoder == nil {
                // mark this engine as underway before compiling to handle recursive types.
                info.encoder = new(encEngine)
                info.encoder = enc.compileEnc(rt)
        }
        return info.encoder
}

// Put this in a function so we can hold the lock only while compiling, not when encoding.
func (enc *Encoder) lockAndGetEncEngine(rt reflect.Type) *encEngine {
        typeLock.Lock()
        defer typeLock.Unlock()
        return enc.getEncEngine(rt)
}

func (enc *Encoder) encode(b *bytes.Buffer, value reflect.Value) (err os.Error) {
        defer catchError(&err)
        // Dereference down to the underlying object.
        rt, indir := indirect(value.Type())
        for i := 0; i < indir; i++ {
                value = reflect.Indirect(value)
        }
        engine := enc.lockAndGetEncEngine(rt)
        if value.Type().Kind() == reflect.Struct {
                enc.encodeStruct(b, engine, value.Addr())
        } else {
                enc.encodeSingle(b, engine, value.Addr())
        }
        return nil
}