kesavand | c71914f | 2022-03-25 11:19:03 +0530 | [diff] [blame] | 1 | // Copyright 2018 Klaus Post. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | // Based on work Copyright (c) 2013, Yann Collet, released under BSD License. |
| 5 | |
| 6 | package zstd |
| 7 | |
| 8 | import "fmt" |
| 9 | |
| 10 | // bitWriter will write bits. |
| 11 | // First bit will be LSB of the first byte of output. |
| 12 | type bitWriter struct { |
| 13 | bitContainer uint64 |
| 14 | nBits uint8 |
| 15 | out []byte |
| 16 | } |
| 17 | |
| 18 | // bitMask16 is bitmasks. Has extra to avoid bounds check. |
| 19 | var bitMask16 = [32]uint16{ |
| 20 | 0, 1, 3, 7, 0xF, 0x1F, |
| 21 | 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, |
| 22 | 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0xFFFF, |
| 23 | 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, |
| 24 | 0xFFFF, 0xFFFF} /* up to 16 bits */ |
| 25 | |
| 26 | var bitMask32 = [32]uint32{ |
| 27 | 0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF, |
| 28 | 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, |
| 29 | 0x1ffff, 0x3ffff, 0x7FFFF, 0xfFFFF, 0x1fFFFF, 0x3fFFFF, 0x7fFFFF, 0xffFFFF, |
| 30 | 0x1ffFFFF, 0x3ffFFFF, 0x7ffFFFF, 0xfffFFFF, 0x1fffFFFF, 0x3fffFFFF, 0x7fffFFFF, |
| 31 | } // up to 32 bits |
| 32 | |
| 33 | // addBits16NC will add up to 16 bits. |
| 34 | // It will not check if there is space for them, |
| 35 | // so the caller must ensure that it has flushed recently. |
| 36 | func (b *bitWriter) addBits16NC(value uint16, bits uint8) { |
| 37 | b.bitContainer |= uint64(value&bitMask16[bits&31]) << (b.nBits & 63) |
| 38 | b.nBits += bits |
| 39 | } |
| 40 | |
| 41 | // addBits32NC will add up to 31 bits. |
| 42 | // It will not check if there is space for them, |
| 43 | // so the caller must ensure that it has flushed recently. |
| 44 | func (b *bitWriter) addBits32NC(value uint32, bits uint8) { |
| 45 | b.bitContainer |= uint64(value&bitMask32[bits&31]) << (b.nBits & 63) |
| 46 | b.nBits += bits |
| 47 | } |
| 48 | |
| 49 | // addBits64NC will add up to 64 bits. |
| 50 | // There must be space for 32 bits. |
| 51 | func (b *bitWriter) addBits64NC(value uint64, bits uint8) { |
| 52 | if bits <= 31 { |
| 53 | b.addBits32Clean(uint32(value), bits) |
| 54 | return |
| 55 | } |
| 56 | b.addBits32Clean(uint32(value), 32) |
| 57 | b.flush32() |
| 58 | b.addBits32Clean(uint32(value>>32), bits-32) |
| 59 | } |
| 60 | |
| 61 | // addBits32Clean will add up to 32 bits. |
| 62 | // It will not check if there is space for them. |
| 63 | // The input must not contain more bits than specified. |
| 64 | func (b *bitWriter) addBits32Clean(value uint32, bits uint8) { |
| 65 | b.bitContainer |= uint64(value) << (b.nBits & 63) |
| 66 | b.nBits += bits |
| 67 | } |
| 68 | |
| 69 | // addBits16Clean will add up to 16 bits. value may not contain more set bits than indicated. |
| 70 | // It will not check if there is space for them, so the caller must ensure that it has flushed recently. |
| 71 | func (b *bitWriter) addBits16Clean(value uint16, bits uint8) { |
| 72 | b.bitContainer |= uint64(value) << (b.nBits & 63) |
| 73 | b.nBits += bits |
| 74 | } |
| 75 | |
| 76 | // flush will flush all pending full bytes. |
| 77 | // There will be at least 56 bits available for writing when this has been called. |
| 78 | // Using flush32 is faster, but leaves less space for writing. |
| 79 | func (b *bitWriter) flush() { |
| 80 | v := b.nBits >> 3 |
| 81 | switch v { |
| 82 | case 0: |
| 83 | case 1: |
| 84 | b.out = append(b.out, |
| 85 | byte(b.bitContainer), |
| 86 | ) |
| 87 | case 2: |
| 88 | b.out = append(b.out, |
| 89 | byte(b.bitContainer), |
| 90 | byte(b.bitContainer>>8), |
| 91 | ) |
| 92 | case 3: |
| 93 | b.out = append(b.out, |
| 94 | byte(b.bitContainer), |
| 95 | byte(b.bitContainer>>8), |
| 96 | byte(b.bitContainer>>16), |
| 97 | ) |
| 98 | case 4: |
| 99 | b.out = append(b.out, |
| 100 | byte(b.bitContainer), |
| 101 | byte(b.bitContainer>>8), |
| 102 | byte(b.bitContainer>>16), |
| 103 | byte(b.bitContainer>>24), |
| 104 | ) |
| 105 | case 5: |
| 106 | b.out = append(b.out, |
| 107 | byte(b.bitContainer), |
| 108 | byte(b.bitContainer>>8), |
| 109 | byte(b.bitContainer>>16), |
| 110 | byte(b.bitContainer>>24), |
| 111 | byte(b.bitContainer>>32), |
| 112 | ) |
| 113 | case 6: |
| 114 | b.out = append(b.out, |
| 115 | byte(b.bitContainer), |
| 116 | byte(b.bitContainer>>8), |
| 117 | byte(b.bitContainer>>16), |
| 118 | byte(b.bitContainer>>24), |
| 119 | byte(b.bitContainer>>32), |
| 120 | byte(b.bitContainer>>40), |
| 121 | ) |
| 122 | case 7: |
| 123 | b.out = append(b.out, |
| 124 | byte(b.bitContainer), |
| 125 | byte(b.bitContainer>>8), |
| 126 | byte(b.bitContainer>>16), |
| 127 | byte(b.bitContainer>>24), |
| 128 | byte(b.bitContainer>>32), |
| 129 | byte(b.bitContainer>>40), |
| 130 | byte(b.bitContainer>>48), |
| 131 | ) |
| 132 | case 8: |
| 133 | b.out = append(b.out, |
| 134 | byte(b.bitContainer), |
| 135 | byte(b.bitContainer>>8), |
| 136 | byte(b.bitContainer>>16), |
| 137 | byte(b.bitContainer>>24), |
| 138 | byte(b.bitContainer>>32), |
| 139 | byte(b.bitContainer>>40), |
| 140 | byte(b.bitContainer>>48), |
| 141 | byte(b.bitContainer>>56), |
| 142 | ) |
| 143 | default: |
| 144 | panic(fmt.Errorf("bits (%d) > 64", b.nBits)) |
| 145 | } |
| 146 | b.bitContainer >>= v << 3 |
| 147 | b.nBits &= 7 |
| 148 | } |
| 149 | |
| 150 | // flush32 will flush out, so there are at least 32 bits available for writing. |
| 151 | func (b *bitWriter) flush32() { |
| 152 | if b.nBits < 32 { |
| 153 | return |
| 154 | } |
| 155 | b.out = append(b.out, |
| 156 | byte(b.bitContainer), |
| 157 | byte(b.bitContainer>>8), |
| 158 | byte(b.bitContainer>>16), |
| 159 | byte(b.bitContainer>>24)) |
| 160 | b.nBits -= 32 |
| 161 | b.bitContainer >>= 32 |
| 162 | } |
| 163 | |
| 164 | // flushAlign will flush remaining full bytes and align to next byte boundary. |
| 165 | func (b *bitWriter) flushAlign() { |
| 166 | nbBytes := (b.nBits + 7) >> 3 |
| 167 | for i := uint8(0); i < nbBytes; i++ { |
| 168 | b.out = append(b.out, byte(b.bitContainer>>(i*8))) |
| 169 | } |
| 170 | b.nBits = 0 |
| 171 | b.bitContainer = 0 |
| 172 | } |
| 173 | |
| 174 | // close will write the alignment bit and write the final byte(s) |
| 175 | // to the output. |
| 176 | func (b *bitWriter) close() error { |
| 177 | // End mark |
| 178 | b.addBits16Clean(1, 1) |
| 179 | // flush until next byte. |
| 180 | b.flushAlign() |
| 181 | return nil |
| 182 | } |
| 183 | |
| 184 | // reset and continue writing by appending to out. |
| 185 | func (b *bitWriter) reset(out []byte) { |
| 186 | b.bitContainer = 0 |
| 187 | b.nBits = 0 |
| 188 | b.out = out |
| 189 | } |