81ec6b1d4c
* core/vm: reverse bit order in bytes of code bitmap This bit order is more natural for bit manipulation operations and we can eliminate some small number of CPU instructions. * core/vm: drop lookup table
119 lines
3.1 KiB
Go
119 lines
3.1 KiB
Go
// Copyright 2014 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package vm
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const (
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set2BitsMask = uint16(0b11)
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set3BitsMask = uint16(0b111)
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set4BitsMask = uint16(0b1111)
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set5BitsMask = uint16(0b1_1111)
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set6BitsMask = uint16(0b11_1111)
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set7BitsMask = uint16(0b111_1111)
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)
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// bitvec is a bit vector which maps bytes in a program.
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// An unset bit means the byte is an opcode, a set bit means
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// it's data (i.e. argument of PUSHxx).
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type bitvec []byte
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func (bits bitvec) set1(pos uint64) {
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bits[pos/8] |= 1 << (pos % 8)
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}
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func (bits bitvec) setN(flag uint16, pos uint64) {
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a := flag << (pos % 8)
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bits[pos/8] |= byte(a)
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if b := byte(a >> 8); b != 0 {
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bits[pos/8+1] = b
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}
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}
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func (bits bitvec) set8(pos uint64) {
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a := byte(0xFF << (pos % 8))
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bits[pos/8] |= a
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bits[pos/8+1] = ^a
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}
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func (bits bitvec) set16(pos uint64) {
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a := byte(0xFF << (pos % 8))
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bits[pos/8] |= a
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bits[pos/8+1] = 0xFF
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bits[pos/8+2] = ^a
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}
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// codeSegment checks if the position is in a code segment.
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func (bits *bitvec) codeSegment(pos uint64) bool {
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return (((*bits)[pos/8] >> (pos % 8)) & 1) == 0
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}
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// codeBitmap collects data locations in code.
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func codeBitmap(code []byte) bitvec {
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// The bitmap is 4 bytes longer than necessary, in case the code
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// ends with a PUSH32, the algorithm will push zeroes onto the
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// bitvector outside the bounds of the actual code.
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bits := make(bitvec, len(code)/8+1+4)
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return codeBitmapInternal(code, bits)
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}
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// codeBitmapInternal is the internal implementation of codeBitmap.
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// It exists for the purpose of being able to run benchmark tests
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// without dynamic allocations affecting the results.
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func codeBitmapInternal(code, bits bitvec) bitvec {
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for pc := uint64(0); pc < uint64(len(code)); {
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op := OpCode(code[pc])
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pc++
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if op < PUSH1 || op > PUSH32 {
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continue
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}
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numbits := op - PUSH1 + 1
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if numbits >= 8 {
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for ; numbits >= 16; numbits -= 16 {
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bits.set16(pc)
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pc += 16
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}
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for ; numbits >= 8; numbits -= 8 {
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bits.set8(pc)
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pc += 8
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}
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}
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switch numbits {
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case 1:
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bits.set1(pc)
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pc += 1
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case 2:
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bits.setN(set2BitsMask, pc)
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pc += 2
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case 3:
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bits.setN(set3BitsMask, pc)
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pc += 3
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case 4:
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bits.setN(set4BitsMask, pc)
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pc += 4
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case 5:
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bits.setN(set5BitsMask, pc)
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pc += 5
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case 6:
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bits.setN(set6BitsMask, pc)
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pc += 6
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case 7:
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bits.setN(set7BitsMask, pc)
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pc += 7
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}
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}
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return bits
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}
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