forked from toolshed/abra
113 lines
3.4 KiB
Go
113 lines
3.4 KiB
Go
// Copyright 2018 Klaus Post. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
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package zstd
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// bitWriter will write bits.
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// First bit will be LSB of the first byte of output.
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type bitWriter struct {
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bitContainer uint64
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nBits uint8
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out []byte
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}
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// bitMask16 is bitmasks. Has extra to avoid bounds check.
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var bitMask16 = [32]uint16{
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0, 1, 3, 7, 0xF, 0x1F,
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0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
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0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0xFFFF,
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0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF,
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0xFFFF, 0xFFFF} /* up to 16 bits */
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var bitMask32 = [32]uint32{
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0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF,
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0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF,
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0x1ffff, 0x3ffff, 0x7FFFF, 0xfFFFF, 0x1fFFFF, 0x3fFFFF, 0x7fFFFF, 0xffFFFF,
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0x1ffFFFF, 0x3ffFFFF, 0x7ffFFFF, 0xfffFFFF, 0x1fffFFFF, 0x3fffFFFF, 0x7fffFFFF,
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} // up to 32 bits
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// addBits16NC will add up to 16 bits.
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// It will not check if there is space for them,
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// so the caller must ensure that it has flushed recently.
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func (b *bitWriter) addBits16NC(value uint16, bits uint8) {
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b.bitContainer |= uint64(value&bitMask16[bits&31]) << (b.nBits & 63)
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b.nBits += bits
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}
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// addBits32NC will add up to 31 bits.
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// It will not check if there is space for them,
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// so the caller must ensure that it has flushed recently.
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func (b *bitWriter) addBits32NC(value uint32, bits uint8) {
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b.bitContainer |= uint64(value&bitMask32[bits&31]) << (b.nBits & 63)
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b.nBits += bits
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}
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// addBits64NC will add up to 64 bits.
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// There must be space for 32 bits.
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func (b *bitWriter) addBits64NC(value uint64, bits uint8) {
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if bits <= 31 {
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b.addBits32Clean(uint32(value), bits)
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return
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}
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b.addBits32Clean(uint32(value), 32)
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b.flush32()
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b.addBits32Clean(uint32(value>>32), bits-32)
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}
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// addBits32Clean will add up to 32 bits.
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// It will not check if there is space for them.
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// The input must not contain more bits than specified.
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func (b *bitWriter) addBits32Clean(value uint32, bits uint8) {
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b.bitContainer |= uint64(value) << (b.nBits & 63)
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b.nBits += bits
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}
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// addBits16Clean will add up to 16 bits. value may not contain more set bits than indicated.
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// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
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func (b *bitWriter) addBits16Clean(value uint16, bits uint8) {
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b.bitContainer |= uint64(value) << (b.nBits & 63)
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b.nBits += bits
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}
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// flush32 will flush out, so there are at least 32 bits available for writing.
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func (b *bitWriter) flush32() {
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if b.nBits < 32 {
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return
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}
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b.out = append(b.out,
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byte(b.bitContainer),
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byte(b.bitContainer>>8),
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byte(b.bitContainer>>16),
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byte(b.bitContainer>>24))
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b.nBits -= 32
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b.bitContainer >>= 32
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}
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// flushAlign will flush remaining full bytes and align to next byte boundary.
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func (b *bitWriter) flushAlign() {
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nbBytes := (b.nBits + 7) >> 3
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for i := uint8(0); i < nbBytes; i++ {
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b.out = append(b.out, byte(b.bitContainer>>(i*8)))
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}
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b.nBits = 0
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b.bitContainer = 0
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}
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// close will write the alignment bit and write the final byte(s)
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// to the output.
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func (b *bitWriter) close() {
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// End mark
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b.addBits16Clean(1, 1)
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// flush until next byte.
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b.flushAlign()
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}
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// reset and continue writing by appending to out.
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func (b *bitWriter) reset(out []byte) {
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b.bitContainer = 0
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b.nBits = 0
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b.out = out
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}
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