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decoder_fast_next.go
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/
decoder_fast_next.go
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// Copyright 2016 The Vanadium 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 vom
import (
"strconv"
"v.io/v23/vdl"
)
// This file contains the NextEntryValue* methods. The semantics of these
// methods is the same as if NextEntry, StartValue, Decode*, FinishValue were
// called in sequence. The implementation is faster than actually calling that
// sequence, because we minimize the work done in the inner loop.
//
// Here's what the regular sequence of calls looks like, without error handling:
// for {
// done, _ := dec.NextEntry() // Increments index
// if done {
// return nil
// }
// dec.StartValue() // Pushes type onto stack
// value, _ := dec.DecodeBool() // Decodes the value
// dec.FinishValue() // Pops type off of stack
// }
//
// Here's what the NextEntryValue call looks like:
// for {
// done, value, _ := dec.NextEntryValueBool()
// if done {
// return nil
// }
// }
//
// So far, we've reduced the 4 calls through the Decoder interface into 1 call,
// but if we just implemented exactly the same logic it wouldn't be much faster.
// The real speedup comes because in the common case, the type of the entry is
// static (i.e. not Any), so we can skip pushing and popping the stack, and also
// skip checking compatibility. Instead we only perform this once, the first
// time through the loop, and each subsequent call has a fastpath.
//
// Each method as the same pattern:
//
// NextEntry:
// Increments the index, and check if we're done.
// Check fastpath:
// The NextEntryType field on the containing collection tells us whether the
// fastpath has been enabled. E.g. if []int32 is at the top of the stack, its
// NextEntryType field will be Int32Type. We initialize this on the first
// call, by running the equivalent of StartValue and checking compatibility.
// There's no need to push the stack, since we have the NextEntryType field to
// remind us that all this work has been done. We can't use the fastpath for
// Any types, since we'll always need to decode the Any header and check
// compatibility
// Decode:
// We implement common-case fastpaths; e.g. avoiding unnecessary conversions.
type nextEntryData int
const (
// We store extra information about the next type in the decoder flags, so we
// don't need to recompute it for each entry.
//
// For number types, bits [8,15] store the bitlen, and we have two special
// sentry flags. The sentries must be > any valid bitlen.
nextEntryMustConvert nextEntryData = 0x0100 // must convert value
nextEntryParentBytes nextEntryData = 0x0200 // parent is []byte
// TODO(toddw): VDL currently doesn't support Optional scalars, but if we were
// to add this support, we'd need to set an extra bit in nextEntryData to
// remind us to decode the Optional header.
)
func (d *decoder81) NextEntryValueBool() (done bool, value bool, err error) {
// NextEntry
top := d.top()
if top == nil {
return false, false, errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, false, nil
}
// Check fastpath
if top.NextEntryType != nil {
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
var ttNext *vdl.Type
if ttNext, err = d.dfsNextType(); err != nil {
return false, false, err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, false, err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility
switch ttNext.Kind() {
case vdl.Bool:
default:
return false, false, errIncompatibleDecode(ttNext, "bool")
}
}
// Decode
value, err = binaryDecodeBool(d.buf)
return false, value, err
}
func (d *decoder81) NextEntryValueString() (done bool, value string, err error) {
// NextEntry
top := d.top()
if top == nil {
return false, "", errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, "", nil
}
// Check fastpath
var ttNext *vdl.Type
if top.NextEntryType != nil {
ttNext = top.NextEntryType
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
if ttNext, err = d.dfsNextType(); err != nil {
return false, "", err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, "", err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility
switch ttNext.Kind() {
case vdl.String, vdl.Enum:
default:
return false, "", errIncompatibleDecode(ttNext, "string")
}
}
// Decode
switch ttNext.Kind() {
case vdl.String:
value, err = binaryDecodeString(d.buf)
case vdl.Enum:
value, err = d.binaryDecodeEnum(ttNext)
}
return false, value, err
}
func (d *decoder81) NextEntryValueUint(bitlen int) (done bool, value uint64, err error) { //nolint:gocyclo
// NextEntry
top := d.top()
if top == nil {
return false, 0, errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, 0, nil
}
// Check fastpath
var ttNext *vdl.Type
if top.NextEntryType != nil {
ttNext = top.NextEntryType
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
if ttNext, err = d.dfsNextType(); err != nil {
return false, 0, err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, 0, err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility, and set NextEntryData.
switch ttNext.Kind() {
case vdl.Uint16, vdl.Uint32, vdl.Uint64:
top.NextEntryData = nextEntryData(ttNext.Kind().BitLen())
case vdl.Int8, vdl.Int16, vdl.Int32, vdl.Int64, vdl.Float32, vdl.Float64:
top.NextEntryData = nextEntryMustConvert
case vdl.Byte:
if d.flag.IsParentBytes() {
top.NextEntryData = nextEntryParentBytes
} else {
top.NextEntryData = 8 // byte is 8 bits
}
default:
return false, 0, errIncompatibleDecode(ttNext, "uint"+strconv.Itoa(bitlen))
}
}
// Decode, avoiding unnecessary number conversions.
switch flag := top.NextEntryData; {
case flag <= nextEntryData(bitlen):
value, err = binaryDecodeUint(d.buf)
case flag == nextEntryParentBytes:
if d.buf.IsAvailable(1) {
value = uint64(d.buf.ReadAvailableByte())
} else if err = d.buf.Fill(1); err == nil {
value = uint64(d.buf.ReadAvailableByte())
}
default: // must convert
value, err = d.decodeUint(ttNext, uint(bitlen))
}
return false, value, err
}
func (d *decoder81) NextEntryValueInt(bitlen int) (done bool, value int64, err error) {
// NextEntry
top := d.top()
if top == nil {
return false, 0, errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, 0, nil
}
// Check fastpath
var ttNext *vdl.Type
if top.NextEntryType != nil {
ttNext = top.NextEntryType
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
if ttNext, err = d.dfsNextType(); err != nil {
return false, 0, err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, 0, err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility, and set NextEntryData.
switch ttNext.Kind() {
case vdl.Int8, vdl.Int16, vdl.Int32, vdl.Int64:
top.NextEntryData = nextEntryData(ttNext.Kind().BitLen())
case vdl.Byte, vdl.Uint16, vdl.Uint32, vdl.Uint64, vdl.Float32, vdl.Float64:
top.NextEntryData = nextEntryMustConvert
default:
return false, 0, errIncompatibleDecode(ttNext, "int"+strconv.Itoa(bitlen))
}
}
// Decode, avoiding unnecessary number conversions.
switch flag := top.NextEntryData; {
case flag <= nextEntryData(bitlen):
value, err = binaryDecodeInt(d.buf)
default: // must convert
value, err = d.decodeInt(ttNext, uint(bitlen))
}
return false, value, err
}
func (d *decoder81) NextEntryValueFloat(bitlen int) (done bool, value float64, err error) {
// NextEntry
top := d.top()
if top == nil {
return false, 0, errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, 0, nil
}
// Check fastpath
var ttNext *vdl.Type
if top.NextEntryType != nil {
ttNext = top.NextEntryType
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
if ttNext, err = d.dfsNextType(); err != nil {
return false, 0, err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, 0, err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility, and set NextEntryData.
switch ttNext.Kind() {
case vdl.Float32, vdl.Float64:
top.NextEntryData = nextEntryData(ttNext.Kind().BitLen())
case vdl.Byte, vdl.Uint16, vdl.Uint32, vdl.Uint64, vdl.Int8, vdl.Int16, vdl.Int32, vdl.Int64:
top.NextEntryData = nextEntryMustConvert
default:
return false, 0, errIncompatibleDecode(ttNext, "float"+strconv.Itoa(bitlen))
}
}
// Decode, avoiding unnecessary number conversions.
switch flag := top.NextEntryData; {
case flag <= nextEntryData(bitlen):
value, err = binaryDecodeFloat(d.buf)
default: // must convert
value, err = d.decodeFloat(ttNext, uint(bitlen))
}
return false, value, err
}
func (d *decoder81) NextEntryValueTypeObject() (done bool, value *vdl.Type, err error) {
// NextEntry
top := d.top()
if top == nil {
return false, nil, errEmptyDecoderStack
}
top.Index++
if top.Index == top.LenHint {
return true, nil, nil
}
// Check fastpath
if top.NextEntryType != nil {
if top.Type.Kind() == vdl.Map {
top.Flag = top.Flag.FlipIsMapKey()
}
} else {
// StartValue
var ttNext *vdl.Type
if ttNext, err = d.dfsNextType(); err != nil {
return false, nil, err
}
var flag decStackFlag
if ttNext, _, flag, err = d.setupType(ttNext, nil); err != nil {
return false, nil, err
}
if !flag.IsAny() { // can't enable fastpath for Any types.
top.NextEntryType = ttNext
}
// Check compatibility
switch ttNext.Kind() {
case vdl.TypeObject:
default:
return false, nil, errIncompatibleDecode(ttNext, "typeobject")
}
}
// Decode
value, err = d.binaryDecodeType()
return false, value, err
}