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core/vm: reverse bit order in bytes of code bitmap (#24120)

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* 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
This commit is contained in:
Paweł Bylica
2021-12-17 10:32:00 +01:00
committed by GitHub
parent bc6bf1e193
commit 81ec6b1d4c
2 changed files with 35 additions and 37 deletions
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32
core/vm/analysis.go
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@ -17,12 +17,12 @@
package vm
const (
set2BitsMask = uint16(0b1100_0000_0000_0000)
set3BitsMask = uint16(0b1110_0000_0000_0000)
set4BitsMask = uint16(0b1111_0000_0000_0000)
set5BitsMask = uint16(0b1111_1000_0000_0000)
set6BitsMask = uint16(0b1111_1100_0000_0000)
set7BitsMask = uint16(0b1111_1110_0000_0000)
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.
@ -30,32 +30,26 @@ const (
// 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) set1(pos uint64) {
bits[pos/8] |= lookup[pos%8]
bits[pos/8] |= 1 << (pos % 8)
}
func (bits bitvec) setN(flag uint16, pos uint64) {
a := flag >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
// If the bit-setting affects the neighbouring byte, we can assign - no need to OR it,
// since it's the first write to that byte
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))
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))
a := byte(0xFF << (pos % 8))
bits[pos/8] |= a
bits[pos/8+1] = 0xFF
bits[pos/8+2] = ^a
@ -63,7 +57,7 @@ func (bits bitvec) set16(pos uint64) {
// 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
return (((*bits)[pos/8] >> (pos % 8)) & 1) == 0
}
// codeBitmap collects data locations in code.