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core/vm: improve bitvec comments

This commit is contained in:
Felix Lange 2017-09-10 21:04:36 +02:00 committed by GitHub
parent d6681ed360
commit 42a5b54bf5
1 changed files with 7 additions and 7 deletions
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14
core/vm/analysis.go
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@ -44,8 +44,9 @@ func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool
return OpCode(code[udest]) == JUMPDEST && m.codeSegment(udest) return OpCode(code[udest]) == JUMPDEST && m.codeSegment(udest)
} }
// bitvec is a bit vector which maps bytes in a program // bitvec is a bit vector which maps bytes in a program.
// An unset bit means the byte is a code-segemnt, a set bit means it's data-segment // An unset bit means the byte is an opcode, a set bit means
// it's data (i.e. argument of PUSHxx).
type bitvec []byte type bitvec []byte
func (bits *bitvec) set(pos uint64) { func (bits *bitvec) set(pos uint64) {
@ -56,15 +57,14 @@ func (bits *bitvec) set8(pos uint64) {
(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8)) (*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))
} }
// codeSegment checks if the position is in a code segment // codeSegment checks if the position is in a code segment.
func (bits *bitvec) codeSegment(pos uint64) bool { func (bits *bitvec) codeSegment(pos uint64) bool {
return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0 return ((*bits)[pos/8] & (0x80 >> (pos % 8))) == 0
} }
// jumpdests creates a bitmap of the code, where 1 represents a DATA-segment, // codeBitmap collects data locations in code.
// and 0 represents code-segment func codeBitmap(code []byte) bitvec {
func codeBitmap(code []byte) []byte { // The bitmap is 4 bytes longer than necessary, in case the code
//The map is 4 bytes longer than necessary, in case the code
// ends with a PUSH32, the algorithm will push zeroes onto the // ends with a PUSH32, the algorithm will push zeroes onto the
// bitvector outside the bounds of the actual code. // bitvector outside the bounds of the actual code.
bits := make(bitvec, len(code)/8+1+4) bits := make(bitvec, len(code)/8+1+4)