forked from mirror/brotli
57 lines
1.5 KiB
Go
57 lines
1.5 KiB
Go
package brotli
|
|
|
|
/* 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) {
|
|
var array_pos []byte = array[*pos>>3:]
|
|
var bits_reserved_in_first_byte uint = (*pos & 7)
|
|
/* implicit & 0xFF is assumed for uint8_t arithmetics */
|
|
|
|
var bits_left_to_write uint
|
|
bits <<= bits_reserved_in_first_byte
|
|
array_pos[0] |= byte(bits)
|
|
array_pos = array_pos[1:]
|
|
for bits_left_to_write = n_bits + bits_reserved_in_first_byte; bits_left_to_write >= 9; bits_left_to_write -= 8 {
|
|
bits >>= 8
|
|
array_pos[0] = byte(bits)
|
|
array_pos = array_pos[1:]
|
|
}
|
|
|
|
array_pos[0] = 0
|
|
*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
|
|
}
|