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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 fakevm
const (
set2BitsMask = uint16(0b11)
set3BitsMask = uint16(0b111)
set4BitsMask = uint16(0b1111)
set5BitsMask = uint16(0b1_1111)
set6BitsMask = uint16(0b11_1111)
set7BitsMask = uint16(0b111_1111)
)
// 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
func (bits bitvec) set1(pos uint64) {
bits[pos/8] |= 1 << (pos % 8)
}
func (bits bitvec) setN(flag uint16, pos uint64) {
a := flag << (pos % 8)
bits[pos/8] |= byte(a)
if b := byte(a >> 8); b != 0 {
bits[pos/8+1] = b
}
}
func (bits bitvec) set8(pos uint64) {
a := byte(0xFF << (pos % 8))
bits[pos/8] |= a
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
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] >> (pos % 8)) & 1) == 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 int8(op) < int8(PUSH1) { // If not PUSH (the int8(op) > int(PUSH32) is always false).
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.set1(pc)
pc += 1
case 2:
bits.setN(set2BitsMask, pc)
pc += 2
case 3:
bits.setN(set3BitsMask, pc)
pc += 3
case 4:
bits.setN(set4BitsMask, pc)
pc += 4
case 5:
bits.setN(set5BitsMask, pc)
pc += 5
case 6:
bits.setN(set6BitsMask, pc)
pc += 6
case 7:
bits.setN(set7BitsMask, pc)
pc += 7
}
}
return bits
}