forgejo-federation/vendor/github.com/andybalholm/brotli/write_bits.go

57 lines
1.5 KiB
Go
Raw Normal View History

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
}