57 lines
1.5 KiB
Go
57 lines
1.5 KiB
Go
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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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/* This function writes bits into bytes in increasing addresses, and within
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a byte least-significant-bit first.
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The function can write up to 56 bits in one go with WriteBits
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Example: let's assume that 3 bits (Rs below) have been written already:
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BYTE-0 BYTE+1 BYTE+2
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0000 0RRR 0000 0000 0000 0000
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Now, we could write 5 or less bits in MSB by just sifting by 3
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and OR'ing to BYTE-0.
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For n bits, we take the last 5 bits, OR that with high bits in BYTE-0,
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and locate the rest in BYTE+1, BYTE+2, etc. */
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func writeBits(n_bits uint, bits uint64, pos *uint, array []byte) {
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var array_pos []byte = array[*pos>>3:]
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var bits_reserved_in_first_byte uint = (*pos & 7)
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/* implicit & 0xFF is assumed for uint8_t arithmetics */
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var bits_left_to_write uint
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bits <<= bits_reserved_in_first_byte
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array_pos[0] |= byte(bits)
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array_pos = array_pos[1:]
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for bits_left_to_write = n_bits + bits_reserved_in_first_byte; bits_left_to_write >= 9; bits_left_to_write -= 8 {
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bits >>= 8
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array_pos[0] = byte(bits)
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array_pos = array_pos[1:]
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}
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array_pos[0] = 0
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*pos += n_bits
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}
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func writeSingleBit(bit bool, pos *uint, array []byte) {
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if bit {
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writeBits(1, 1, pos, array)
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} else {
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writeBits(1, 0, pos, array)
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}
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}
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func writeBitsPrepareStorage(pos uint, array []byte) {
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assert(pos&7 == 0)
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array[pos>>3] = 0
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}
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