53 lines
1.5 KiB
Go
53 lines
1.5 KiB
Go
package brotli
|
|
|
|
import "encoding/binary"
|
|
|
|
/* Copyright 2010 Google Inc. All Rights Reserved.
|
|
|
|
Distributed under MIT license.
|
|
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
|
|
*/
|
|
|
|
/* Write bits into a byte array. */
|
|
|
|
/* This function writes bits into bytes in increasing addresses, and within
|
|
a byte least-significant-bit first.
|
|
|
|
The function can write up to 56 bits in one go with WriteBits
|
|
Example: let's assume that 3 bits (Rs below) have been written already:
|
|
|
|
BYTE-0 BYTE+1 BYTE+2
|
|
|
|
0000 0RRR 0000 0000 0000 0000
|
|
|
|
Now, we could write 5 or less bits in MSB by just sifting by 3
|
|
and OR'ing to BYTE-0.
|
|
|
|
For n bits, we take the last 5 bits, OR that with high bits in BYTE-0,
|
|
and locate the rest in BYTE+1, BYTE+2, etc. */
|
|
func writeBits(n_bits uint, bits uint64, pos *uint, array []byte) {
|
|
/* This branch of the code can write up to 56 bits at a time,
|
|
7 bits are lost by being perhaps already in *p and at least
|
|
1 bit is needed to initialize the bit-stream ahead (i.e. if 7
|
|
bits are in *p and we write 57 bits, then the next write will
|
|
access a byte that was never initialized). */
|
|
p := array[*pos>>3:]
|
|
v := uint64(p[0])
|
|
v |= bits << (*pos & 7)
|
|
binary.LittleEndian.PutUint64(p, v)
|
|
*pos += n_bits
|
|
}
|
|
|
|
func writeSingleBit(bit bool, pos *uint, array []byte) {
|
|
if bit {
|
|
writeBits(1, 1, pos, array)
|
|
} else {
|
|
writeBits(1, 0, pos, array)
|
|
}
|
|
}
|
|
|
|
func writeBitsPrepareStorage(pos uint, array []byte) {
|
|
assert(pos&7 == 0)
|
|
array[pos>>3] = 0
|
|
}
|