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destination.go
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destination.go
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package vm
import (
"github.com/vitelabs/go-vite/common/types"
"math/big"
)
type bitvec []byte
type destinations map[types.Address]bitvec
func (bits *bitvec) set(pos uint64) {
(*bits)[pos/8] |= 0x80 >> (pos % 8)
}
func (bits *bitvec) set8(pos uint64) {
(*bits)[pos/8] |= 0xFF >> (pos % 8)
(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))
}
// codeSegment checks if the position is in a code segment.
func (bits *bitvec) codeSegment(pos uint64) bool {
return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
}
// has checks whether code has a JUMPDEST at dest.
func (d destinations) has(addr types.Address, code []byte, dest *big.Int) bool {
// PC cannot go beyond len(code) and certainly can't be bigger than 63bits.
// Don't bother checking for JUMPDEST in that case.
udest := dest.Uint64()
if dest.BitLen() >= 63 || udest >= uint64(len(code)) {
return false
}
m, analysed := d[addr]
if !analysed {
m = codeBitmap(code)
d[addr] = m
}
return opCode(code[udest]) == JUMPDEST && m.codeSegment(udest)
}
// codeBitmap collects data locations in code.
func codeBitmap(code []byte) bitvec {
// The bitmap is 4 bytes longer than necessary, in case the code
// ends with a PUSH32, the algorithm will push zeroes onto the
// bitvector outside the bounds of the actual code.
bits := make(bitvec, len(code)/8+1+4)
for pc := uint64(0); pc < uint64(len(code)); {
op := opCode(code[pc])
if op >= PUSH1 && op <= PUSH32 {
numbits := op - PUSH1 + 1
pc++
for ; numbits >= 8; numbits -= 8 {
bits.set8(pc) // 8
pc += 8
}
for ; numbits > 0; numbits-- {
bits.set(pc)
pc++
}
} else {
pc++
}
}
return bits
}