/
analysis.go
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/
analysis.go
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// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package vm
// bitvec is a bit vector which maps bytes in a program.
// An unset bit means the byte is an opcode, a set bit means
// it's data (i.e. argument of PUSHxx).
type bitvec []byte
var lookup = [8]byte{
0x80, 0x40, 0x20, 0x10, 0x8, 0x4, 0x2, 0x1,
}
func (bits bitvec) set(pos uint64) {
//(*bits)[pos/8] |= 0x80 >> (pos % 8)
bits[pos/8] |= lookup[pos%8]
}
func (bits bitvec) set2(pos uint64) {
a := uint16(0b1100_0000_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
// If the bit-setting affects the neigbouring byte, we can assign - no need to OR it,
// since it's the first write to that byte
bits[pos/8+1] = b
}
}
func (bits bitvec) set3(pos uint64) {
a := uint16(0b1110_0000_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set4(pos uint64) {
a := uint16(0b1111_0000_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set5(pos uint64) {
a := uint16(0b1111_1000_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set6(pos uint64) {
a := uint16(0b1111_1100_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set7(pos uint64) {
a := uint16(0b1111_1110_0000_0000) >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set8(pos uint64) {
a := byte(0xFF >> (pos % 8))
bits[pos/8] |= a
if ^a != 0 {
bits[pos/8+1] = ^a
}
}
func (bits bitvec) set16(pos uint64) {
a := byte(0xFF >> (pos % 8))
bits[pos/8] |= a
bits[pos/8+1] = 0xFF
if ^a != 0 {
bits[pos/8+2] = ^a
}
}
// 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
}
// 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)
return codeBitmapInternal(code, bits)
}
// codeBitmapInternal is the internal implementation of codeBitmap.
// It exists for the purpose of being able to run benchmark tests
// without dynamic allocations affecting the results.
func codeBitmapInternal(code, bits bitvec) bitvec {
for pc := uint64(0); pc < uint64(len(code)); {
op := OpCode(code[pc])
pc++
if op < PUSH1 || op > PUSH32 {
continue
}
numbits := op - PUSH1 + 1
if numbits >= 8 {
for ; numbits >= 16; numbits -= 16 {
bits.set16(pc)
pc += 16
}
for ; numbits >= 8; numbits -= 8 {
bits.set8(pc)
pc += 8
}
}
switch numbits {
case 1:
bits.set(pc)
pc += 1
case 2:
bits.set2(pc)
pc += 2
case 3:
bits.set3(pc)
pc += 3
case 4:
bits.set4(pc)
pc += 4
case 5:
bits.set5(pc)
pc += 5
case 6:
bits.set6(pc)
pc += 6
case 7:
bits.set7(pc)
pc += 7
}
}
return bits
}