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95 lines
2.0 KiB
95 lines
2.0 KiB
package brotli
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/* Copyright 2010 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* Write bits into a byte array. */
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type bitWriter struct {
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dst []byte
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// Data waiting to be written is the low nbits of bits.
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bits uint64
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nbits uint
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}
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func (w *bitWriter) writeBits(nb uint, b uint64) {
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w.bits |= b << w.nbits
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w.nbits += nb
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if w.nbits >= 32 {
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bits := w.bits
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w.bits >>= 32
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w.nbits -= 32
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w.dst = append(w.dst,
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byte(bits),
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byte(bits>>8),
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byte(bits>>16),
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byte(bits>>24),
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)
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}
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}
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func (w *bitWriter) writeSingleBit(bit bool) {
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if bit {
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w.writeBits(1, 1)
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} else {
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w.writeBits(1, 0)
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}
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}
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func (w *bitWriter) jumpToByteBoundary() {
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dst := w.dst
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for w.nbits != 0 {
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dst = append(dst, byte(w.bits))
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w.bits >>= 8
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if w.nbits > 8 { // Avoid underflow
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w.nbits -= 8
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} else {
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w.nbits = 0
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}
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}
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w.bits = 0
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w.dst = dst
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}
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func (w *bitWriter) writeBytes(b []byte) {
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if w.nbits&7 != 0 {
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panic("writeBytes with unfinished bits")
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}
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for w.nbits != 0 {
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w.dst = append(w.dst, byte(w.bits))
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w.bits >>= 8
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w.nbits -= 8
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}
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w.dst = append(w.dst, b...)
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}
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func (w *bitWriter) getPos() uint {
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return uint(len(w.dst)<<3) + w.nbits
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}
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func (w *bitWriter) rewind(p uint) {
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w.bits = uint64(w.dst[p>>3] & byte((1<<(p&7))-1))
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w.nbits = p & 7
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w.dst = w.dst[:p>>3]
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}
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func (w *bitWriter) updateBits(n_bits uint, bits uint32, pos uint) {
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for n_bits > 0 {
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var byte_pos uint = pos >> 3
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var n_unchanged_bits uint = pos & 7
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var n_changed_bits uint = brotli_min_size_t(n_bits, 8-n_unchanged_bits)
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var total_bits uint = n_unchanged_bits + n_changed_bits
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var mask uint32 = (^((1 << total_bits) - 1)) | ((1 << n_unchanged_bits) - 1)
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var unchanged_bits uint32 = uint32(w.dst[byte_pos]) & mask
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var changed_bits uint32 = bits & ((1 << n_changed_bits) - 1)
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w.dst[byte_pos] = byte(changed_bits<<n_unchanged_bits | unchanged_bits)
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n_bits -= n_changed_bits
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bits >>= n_changed_bits
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pos += n_changed_bits
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}
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}
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