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// SPDX-License-Identifier: Unlicense OR MIT
package ops
import (
"encoding/binary"
)
// Reader parses an ops list.
type Reader struct {
pc PC
stack []macro
ops *Ops
deferOps Ops
deferDone bool
}
// EncodedOp represents an encoded op returned by
// Reader.
type EncodedOp struct {
Key Key
Data []byte
Refs []interface{}
}
// Key is a unique key for a given op.
type Key struct {
ops *Ops
pc int
version int
}
// Shadow of op.MacroOp.
type macroOp struct {
ops *Ops
pc PC
}
// PC is an instruction counter for an operation list.
type PC struct {
data int
refs int
}
type macro struct {
ops *Ops
retPC PC
endPC PC
}
type opMacroDef struct {
endpc PC
}
// Reset start reading from the beginning of ops.
func (r *Reader) Reset(ops *Ops) {
r.ResetAt(ops, PC{})
}
// ResetAt is like Reset, except it starts reading from pc.
func (r *Reader) ResetAt(ops *Ops, pc PC) {
r.stack = r.stack[:0]
Reset(&r.deferOps)
r.deferDone = false
r.pc = pc
r.ops = ops
}
func (r *Reader) Decode() (EncodedOp, bool) {
if r.ops == nil {
return EncodedOp{}, false
}
deferring := false
for {
if len(r.stack) > 0 {
b := r.stack[len(r.stack)-1]
if r.pc == b.endPC {
r.ops = b.ops
r.pc = b.retPC
r.stack = r.stack[:len(r.stack)-1]
continue
}
}
data := r.ops.data
data = data[r.pc.data:]
refs := r.ops.refs
if len(data) == 0 {
if r.deferDone {
return EncodedOp{}, false
}
r.deferDone = true
// Execute deferred macros.
r.ops = &r.deferOps
r.pc = PC{}
continue
}
key := Key{ops: r.ops, pc: r.pc.data, version: r.ops.version}
t := OpType(data[0])
n := t.Size()
nrefs := t.NumRefs()
data = data[:n]
refs = refs[r.pc.refs:]
refs = refs[:nrefs]
switch t {
case TypeDefer:
deferring = true
r.pc.data += n
r.pc.refs += nrefs
continue
case TypeAux:
// An Aux operations is always wrapped in a macro, and
// its length is the remaining space.
block := r.stack[len(r.stack)-1]
n += block.endPC.data - r.pc.data - TypeAuxLen
data = data[:n]
case TypeCall:
if deferring {
deferring = false
// Copy macro for deferred execution.
if t.NumRefs() != 1 {
panic("internal error: unexpected number of macro refs")
}
deferData := Write1(&r.deferOps, t.Size(), refs[0])
copy(deferData, data)
r.pc.data += n
r.pc.refs += nrefs
continue
}
var op macroOp
op.decode(data, refs)
macroData := op.ops.data[op.pc.data:]
if OpType(macroData[0]) != TypeMacro {
panic("invalid macro reference")
}
var opDef opMacroDef
opDef.decode(macroData[:TypeMacro.Size()])
retPC := r.pc
retPC.data += n
retPC.refs += nrefs
r.stack = append(r.stack, macro{
ops: r.ops,
retPC: retPC,
endPC: opDef.endpc,
})
r.ops = op.ops
r.pc = op.pc
r.pc.data += TypeMacro.Size()
r.pc.refs += TypeMacro.NumRefs()
continue
case TypeMacro:
var op opMacroDef
op.decode(data)
r.pc = op.endpc
continue
}
r.pc.data += n
r.pc.refs += nrefs
return EncodedOp{Key: key, Data: data, Refs: refs}, true
}
}
func (op *opMacroDef) decode(data []byte) {
if OpType(data[0]) != TypeMacro {
panic("invalid op")
}
bo := binary.LittleEndian
data = data[:9]
dataIdx := int(int32(bo.Uint32(data[1:])))
refsIdx := int(int32(bo.Uint32(data[5:])))
*op = opMacroDef{
endpc: PC{
data: dataIdx,
refs: refsIdx,
},
}
}
func (m *macroOp) decode(data []byte, refs []interface{}) {
if OpType(data[0]) != TypeCall {
panic("invalid op")
}
data = data[:9]
bo := binary.LittleEndian
dataIdx := int(int32(bo.Uint32(data[1:])))
refsIdx := int(int32(bo.Uint32(data[5:])))
*m = macroOp{
ops: refs[0].(*Ops),
pc: PC{
data: dataIdx,
refs: refsIdx,
},
}
}
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