gtsocial-umbx

encoder.go (9579B)

---

 // Copyright 2021 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 pkgbits
 
 import (
 	"bytes"
 	"crypto/md5"
 	"encoding/binary"
 	"go/constant"
 	"io"
 	"math/big"
 	"runtime"
 )
 
 // currentVersion is the current version number.
 //
 //   - v0: initial prototype
 //
 //   - v1: adds the flags uint32 word
 const currentVersion uint32 = 1
 
 // A PkgEncoder provides methods for encoding a package's Unified IR
 // export data.
 type PkgEncoder struct {
 	// elems holds the bitstream for previously encoded elements.
 	elems [numRelocs][]string
 
 	// stringsIdx maps previously encoded strings to their index within
 	// the RelocString section, to allow deduplication. That is,
 	// elems[RelocString][stringsIdx[s]] == s (if present).
 	stringsIdx map[string]Index
 
 	// syncFrames is the number of frames to write at each sync
 	// marker. A negative value means sync markers are omitted.
 	syncFrames int
 }
 
 // SyncMarkers reports whether pw uses sync markers.
 func (pw *PkgEncoder) SyncMarkers() bool { return pw.syncFrames >= 0 }
 
 // NewPkgEncoder returns an initialized PkgEncoder.
 //
 // syncFrames is the number of caller frames that should be serialized
 // at Sync points. Serializing additional frames results in larger
 // export data files, but can help diagnosing desync errors in
 // higher-level Unified IR reader/writer code. If syncFrames is
 // negative, then sync markers are omitted entirely.
 func NewPkgEncoder(syncFrames int) PkgEncoder {
 	return PkgEncoder{
 		stringsIdx: make(map[string]Index),
 		syncFrames: syncFrames,
 	}
 }
 
 // DumpTo writes the package's encoded data to out0 and returns the
 // package fingerprint.
 func (pw *PkgEncoder) DumpTo(out0 io.Writer) (fingerprint [8]byte) {
 	h := md5.New()
 	out := io.MultiWriter(out0, h)
 
 	writeUint32 := func(x uint32) {
 		assert(binary.Write(out, binary.LittleEndian, x) == nil)
 	}
 
 	writeUint32(currentVersion)
 
 	var flags uint32
 	if pw.SyncMarkers() {
 		flags |= flagSyncMarkers
 	}
 	writeUint32(flags)
 
 	// Write elemEndsEnds.
 	var sum uint32
 	for _, elems := range &pw.elems {
 		sum += uint32(len(elems))
 		writeUint32(sum)
 	}
 
 	// Write elemEnds.
 	sum = 0
 	for _, elems := range &pw.elems {
 		for _, elem := range elems {
 			sum += uint32(len(elem))
 			writeUint32(sum)
 		}
 	}
 
 	// Write elemData.
 	for _, elems := range &pw.elems {
 		for _, elem := range elems {
 			_, err := io.WriteString(out, elem)
 			assert(err == nil)
 		}
 	}
 
 	// Write fingerprint.
 	copy(fingerprint[:], h.Sum(nil))
 	_, err := out0.Write(fingerprint[:])
 	assert(err == nil)
 
 	return
 }
 
 // StringIdx adds a string value to the strings section, if not
 // already present, and returns its index.
 func (pw *PkgEncoder) StringIdx(s string) Index {
 	if idx, ok := pw.stringsIdx[s]; ok {
 		assert(pw.elems[RelocString][idx] == s)
 		return idx
 	}
 
 	idx := Index(len(pw.elems[RelocString]))
 	pw.elems[RelocString] = append(pw.elems[RelocString], s)
 	pw.stringsIdx[s] = idx
 	return idx
 }
 
 // NewEncoder returns an Encoder for a new element within the given
 // section, and encodes the given SyncMarker as the start of the
 // element bitstream.
 func (pw *PkgEncoder) NewEncoder(k RelocKind, marker SyncMarker) Encoder {
 	e := pw.NewEncoderRaw(k)
 	e.Sync(marker)
 	return e
 }
 
 // NewEncoderRaw returns an Encoder for a new element within the given
 // section.
 //
 // Most callers should use NewEncoder instead.
 func (pw *PkgEncoder) NewEncoderRaw(k RelocKind) Encoder {
 	idx := Index(len(pw.elems[k]))
 	pw.elems[k] = append(pw.elems[k], "") // placeholder
 
 	return Encoder{
 		p:   pw,
 		k:   k,
 		Idx: idx,
 	}
 }
 
 // An Encoder provides methods for encoding an individual element's
 // bitstream data.
 type Encoder struct {
 	p *PkgEncoder
 
 	Relocs   []RelocEnt
 	RelocMap map[RelocEnt]uint32
 	Data     bytes.Buffer // accumulated element bitstream data
 
 	encodingRelocHeader bool
 
 	k   RelocKind
 	Idx Index // index within relocation section
 }
 
 // Flush finalizes the element's bitstream and returns its Index.
 func (w *Encoder) Flush() Index {
 	var sb bytes.Buffer // TODO(mdempsky): strings.Builder after #44505 is resolved
 
 	// Backup the data so we write the relocations at the front.
 	var tmp bytes.Buffer
 	io.Copy(&tmp, &w.Data)
 
 	// TODO(mdempsky): Consider writing these out separately so they're
 	// easier to strip, along with function bodies, so that we can prune
 	// down to just the data that's relevant to go/types.
 	if w.encodingRelocHeader {
 		panic("encodingRelocHeader already true; recursive flush?")
 	}
 	w.encodingRelocHeader = true
 	w.Sync(SyncRelocs)
 	w.Len(len(w.Relocs))
 	for _, rEnt := range w.Relocs {
 		w.Sync(SyncReloc)
 		w.Len(int(rEnt.Kind))
 		w.Len(int(rEnt.Idx))
 	}
 
 	io.Copy(&sb, &w.Data)
 	io.Copy(&sb, &tmp)
 	w.p.elems[w.k][w.Idx] = sb.String()
 
 	return w.Idx
 }
 
 func (w *Encoder) checkErr(err error) {
 	if err != nil {
 		errorf("unexpected encoding error: %v", err)
 	}
 }
 
 func (w *Encoder) rawUvarint(x uint64) {
 	var buf [binary.MaxVarintLen64]byte
 	n := binary.PutUvarint(buf[:], x)
 	_, err := w.Data.Write(buf[:n])
 	w.checkErr(err)
 }
 
 func (w *Encoder) rawVarint(x int64) {
 	// Zig-zag encode.
 	ux := uint64(x) << 1
 	if x < 0 {
 		ux = ^ux
 	}
 
 	w.rawUvarint(ux)
 }
 
 func (w *Encoder) rawReloc(r RelocKind, idx Index) int {
 	e := RelocEnt{r, idx}
 	if w.RelocMap != nil {
 		if i, ok := w.RelocMap[e]; ok {
 			return int(i)
 		}
 	} else {
 		w.RelocMap = make(map[RelocEnt]uint32)
 	}
 
 	i := len(w.Relocs)
 	w.RelocMap[e] = uint32(i)
 	w.Relocs = append(w.Relocs, e)
 	return i
 }
 
 func (w *Encoder) Sync(m SyncMarker) {
 	if !w.p.SyncMarkers() {
 		return
 	}
 
 	// Writing out stack frame string references requires working
 	// relocations, but writing out the relocations themselves involves
 	// sync markers. To prevent infinite recursion, we simply trim the
 	// stack frame for sync markers within the relocation header.
 	var frames []string
 	if !w.encodingRelocHeader && w.p.syncFrames > 0 {
 		pcs := make([]uintptr, w.p.syncFrames)
 		n := runtime.Callers(2, pcs)
 		frames = fmtFrames(pcs[:n]...)
 	}
 
 	// TODO(mdempsky): Save space by writing out stack frames as a
 	// linked list so we can share common stack frames.
 	w.rawUvarint(uint64(m))
 	w.rawUvarint(uint64(len(frames)))
 	for _, frame := range frames {
 		w.rawUvarint(uint64(w.rawReloc(RelocString, w.p.StringIdx(frame))))
 	}
 }
 
 // Bool encodes and writes a bool value into the element bitstream,
 // and then returns the bool value.
 //
 // For simple, 2-alternative encodings, the idiomatic way to call Bool
 // is something like:
 //
 //	if w.Bool(x != 0) {
 //		// alternative #1
 //	} else {
 //		// alternative #2
 //	}
 //
 // For multi-alternative encodings, use Code instead.
 func (w *Encoder) Bool(b bool) bool {
 	w.Sync(SyncBool)
 	var x byte
 	if b {
 		x = 1
 	}
 	err := w.Data.WriteByte(x)
 	w.checkErr(err)
 	return b
 }
 
 // Int64 encodes and writes an int64 value into the element bitstream.
 func (w *Encoder) Int64(x int64) {
 	w.Sync(SyncInt64)
 	w.rawVarint(x)
 }
 
 // Uint64 encodes and writes a uint64 value into the element bitstream.
 func (w *Encoder) Uint64(x uint64) {
 	w.Sync(SyncUint64)
 	w.rawUvarint(x)
 }
 
 // Len encodes and writes a non-negative int value into the element bitstream.
 func (w *Encoder) Len(x int) { assert(x >= 0); w.Uint64(uint64(x)) }
 
 // Int encodes and writes an int value into the element bitstream.
 func (w *Encoder) Int(x int) { w.Int64(int64(x)) }
 
 // Uint encodes and writes a uint value into the element bitstream.
 func (w *Encoder) Uint(x uint) { w.Uint64(uint64(x)) }
 
 // Reloc encodes and writes a relocation for the given (section,
 // index) pair into the element bitstream.
 //
 // Note: Only the index is formally written into the element
 // bitstream, so bitstream decoders must know from context which
 // section an encoded relocation refers to.
 func (w *Encoder) Reloc(r RelocKind, idx Index) {
 	w.Sync(SyncUseReloc)
 	w.Len(w.rawReloc(r, idx))
 }
 
 // Code encodes and writes a Code value into the element bitstream.
 func (w *Encoder) Code(c Code) {
 	w.Sync(c.Marker())
 	w.Len(c.Value())
 }
 
 // String encodes and writes a string value into the element
 // bitstream.
 //
 // Internally, strings are deduplicated by adding them to the strings
 // section (if not already present), and then writing a relocation
 // into the element bitstream.
 func (w *Encoder) String(s string) {
 	w.Sync(SyncString)
 	w.Reloc(RelocString, w.p.StringIdx(s))
 }
 
 // Strings encodes and writes a variable-length slice of strings into
 // the element bitstream.
 func (w *Encoder) Strings(ss []string) {
 	w.Len(len(ss))
 	for _, s := range ss {
 		w.String(s)
 	}
 }
 
 // Value encodes and writes a constant.Value into the element
 // bitstream.
 func (w *Encoder) Value(val constant.Value) {
 	w.Sync(SyncValue)
 	if w.Bool(val.Kind() == constant.Complex) {
 		w.scalar(constant.Real(val))
 		w.scalar(constant.Imag(val))
 	} else {
 		w.scalar(val)
 	}
 }
 
 func (w *Encoder) scalar(val constant.Value) {
 	switch v := constant.Val(val).(type) {
 	default:
 		errorf("unhandled %v (%v)", val, val.Kind())
 	case bool:
 		w.Code(ValBool)
 		w.Bool(v)
 	case string:
 		w.Code(ValString)
 		w.String(v)
 	case int64:
 		w.Code(ValInt64)
 		w.Int64(v)
 	case *big.Int:
 		w.Code(ValBigInt)
 		w.bigInt(v)
 	case *big.Rat:
 		w.Code(ValBigRat)
 		w.bigInt(v.Num())
 		w.bigInt(v.Denom())
 	case *big.Float:
 		w.Code(ValBigFloat)
 		w.bigFloat(v)
 	}
 }
 
 func (w *Encoder) bigInt(v *big.Int) {
 	b := v.Bytes()
 	w.String(string(b)) // TODO: More efficient encoding.
 	w.Bool(v.Sign() < 0)
 }
 
 func (w *Encoder) bigFloat(v *big.Float) {
 	b := v.Append(nil, 'p', -1)
 	w.String(string(b)) // TODO: More efficient encoding.
 }