Official Go implementation of the Ethereum protocol
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
go-ethereum/vendor/github.com/steakknife/hamming/popcount.go

135 lines
3.5 KiB

//
// Package hamming distance calculations in Go
//
// https://github.com/steakknife/hamming
//
// Copyright © 2014, 2015, 2016, 2018 Barry Allard
//
// MIT license
//
package hamming
import "strconv"
// References: check out Hacker's Delight, about p. 70
func table() [256]uint8 {
return [256]uint8{
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
}
}
// CountBitsByteAlt table-less, branch-free implementation
func CountBitsByteAlt(x byte) int {
x = (x & 0x55) + ((x >> 1) & 0x55)
x = (x & 0x33) + ((x >> 2) & 0x33)
return int((x & 0x0f) + ((x >> 4) & 0x0f))
}
// CountBitsInt8 count 1's in x
func CountBitsInt8(x int8) int { return CountBitsByte(byte(x)) }
// CountBitsInt16 count 1's in x
func CountBitsInt16(x int16) int { return CountBitsUint16(uint16(x)) }
// CountBitsInt32 count 1's in x
func CountBitsInt32(x int32) int { return CountBitsUint32(uint32(x)) }
// CountBitsInt64 count 1's in x
func CountBitsInt64(x int64) int { return CountBitsUint64(uint64(x)) }
// CountBitsInt count 1's in x
func CountBitsInt(x int) int { return CountBitsUint(uint(x)) }
// CountBitsByte count 1's in x
func CountBitsByte(x byte) int { return CountBitsUint8(x) }
// CountBitsRune count 1's in x
func CountBitsRune(x rune) int { return CountBitsInt32(x) }
// CountBitsUint8 count 1's in x
func CountBitsUint8(x uint8) int { return int(table()[x]) }
// CountBitsUint16 count 1's in x
func CountBitsUint16(x uint16) int {
return int(table()[x&0xFF] + table()[(x>>8)&0xFF])
}
const (
m1d uint32 = 0x55555555
m2d = 0x33333333
m4d = 0x0f0f0f0f
)
// CountBitsUint32 count 1's in x
func CountBitsUint32(x uint32) int {
x -= ((x >> 1) & m1d)
x = (x & m2d) + ((x >> 2) & m2d)
x = (x + (x >> 4)) & m4d
x += x >> 8
x += x >> 16
return int(x & 0x3f)
}
const (
m1q uint64 = 0x5555555555555555
m2q = 0x3333333333333333
m4q = 0x0f0f0f0f0f0f0f0f
hq = 0x0101010101010101
)
// CountBitsUint64 count 1's in x
func CountBitsUint64(x uint64) int {
// put count of each 2 bits into those 2 bits
x -= (x >> 1) & m1q
// put count of each 4 bits into those 4 bits
x = (x & m2q) + ((x >> 2) & m2q)
// put count of each 8 bits into those 8 bits
x = (x + (x >> 4)) & m4q
// returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
return int((x * hq) >> 56)
}
// CountBitsUint64Alt count 1's in x
func CountBitsUint64Alt(x uint64) int {
return CountBitsUint32(uint32(x>>32)) + CountBitsUint32(uint32(x))
}
// CountBitsUintReference count 1's in x
func CountBitsUintReference(x uint) int {
c := 0
for x != 0 {
x &= x - 1
c++
}
return c
}
// CountBitsUint count 1's in x
func CountBitsUint(x uint) int {
if strconv.IntSize == 64 {
return CountBitsUint64(uint64(x))
} else if strconv.IntSize == 32 {
return CountBitsUint32(uint32(x))
}
panic("strconv.IntSize must be 32 or 64 bits")
}