forked from mirror/brotli
95 lines
2.0 KiB
Go
95 lines
2.0 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. */
|
|
|
|
type bitWriter struct {
|
|
dst []byte
|
|
|
|
// Data waiting to be written is the low nbits of bits.
|
|
bits uint64
|
|
nbits uint
|
|
}
|
|
|
|
func (w *bitWriter) writeBits(nb uint, b uint64) {
|
|
w.bits |= b << w.nbits
|
|
w.nbits += nb
|
|
if w.nbits >= 32 {
|
|
bits := w.bits
|
|
w.bits >>= 32
|
|
w.nbits -= 32
|
|
w.dst = append(w.dst,
|
|
byte(bits),
|
|
byte(bits>>8),
|
|
byte(bits>>16),
|
|
byte(bits>>24),
|
|
)
|
|
}
|
|
}
|
|
|
|
func (w *bitWriter) writeSingleBit(bit bool) {
|
|
if bit {
|
|
w.writeBits(1, 1)
|
|
} else {
|
|
w.writeBits(1, 0)
|
|
}
|
|
}
|
|
|
|
func (w *bitWriter) jumpToByteBoundary() {
|
|
dst := w.dst
|
|
for w.nbits != 0 {
|
|
dst = append(dst, byte(w.bits))
|
|
w.bits >>= 8
|
|
if w.nbits > 8 { // Avoid underflow
|
|
w.nbits -= 8
|
|
} else {
|
|
w.nbits = 0
|
|
}
|
|
}
|
|
w.bits = 0
|
|
w.dst = dst
|
|
}
|
|
|
|
func (w *bitWriter) writeBytes(b []byte) {
|
|
if w.nbits&7 != 0 {
|
|
panic("writeBytes with unfinished bits")
|
|
}
|
|
for w.nbits != 0 {
|
|
w.dst = append(w.dst, byte(w.bits))
|
|
w.bits >>= 8
|
|
w.nbits -= 8
|
|
}
|
|
w.dst = append(w.dst, b...)
|
|
}
|
|
|
|
func (w *bitWriter) getPos() uint {
|
|
return uint(len(w.dst)<<3) + w.nbits
|
|
}
|
|
|
|
func (w *bitWriter) rewind(p uint) {
|
|
w.bits = uint64(w.dst[p>>3] & byte((1<<(p&7))-1))
|
|
w.nbits = p & 7
|
|
w.dst = w.dst[:p>>3]
|
|
}
|
|
|
|
func (w *bitWriter) updateBits(n_bits uint, bits uint32, pos uint) {
|
|
for n_bits > 0 {
|
|
var byte_pos uint = pos >> 3
|
|
var n_unchanged_bits uint = pos & 7
|
|
var n_changed_bits uint = brotli_min_size_t(n_bits, 8-n_unchanged_bits)
|
|
var total_bits uint = n_unchanged_bits + n_changed_bits
|
|
var mask uint32 = (^((1 << total_bits) - 1)) | ((1 << n_unchanged_bits) - 1)
|
|
var unchanged_bits uint32 = uint32(w.dst[byte_pos]) & mask
|
|
var changed_bits uint32 = bits & ((1 << n_changed_bits) - 1)
|
|
w.dst[byte_pos] = byte(changed_bits<<n_unchanged_bits | unchanged_bits)
|
|
n_bits -= n_changed_bits
|
|
bits >>= n_changed_bits
|
|
pos += n_changed_bits
|
|
}
|
|
}
|