1 /* Copyright 2013 Google Inc. All Rights Reserved. 2 3 Distributed under MIT license. 4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT 5 */ 6 7 /* This class models a sequence of literals and a backward reference copy. */ 8 9 #ifndef BROTLI_ENC_COMMAND_H_ 10 #define BROTLI_ENC_COMMAND_H_ 11 12 #include "../common/constants.h" 13 #include <brotli/port.h> 14 #include <brotli/types.h> 15 #include "./fast_log.h" 16 #include "./prefix.h" 17 18 #if defined(__cplusplus) || defined(c_plusplus) 19 extern "C" { 20 #endif 21 22 static uint32_t kInsBase[] = { 0, 1, 2, 3, 4, 5, 6, 8, 10, 14, 18, 26, 34, 50, 23 66, 98, 130, 194, 322, 578, 1090, 2114, 6210, 22594 }; 24 static uint32_t kInsExtra[] = { 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 25 5, 5, 6, 7, 8, 9, 10, 12, 14, 24 }; 26 static uint32_t kCopyBase[] = { 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 18, 22, 30, 27 38, 54, 70, 102, 134, 198, 326, 582, 1094, 2118 }; 28 static uint32_t kCopyExtra[] = { 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 29 4, 4, 5, 5, 6, 7, 8, 9, 10, 24 }; 30 31 static BROTLI_INLINE uint16_t GetInsertLengthCode(size_t insertlen) { 32 if (insertlen < 6) { 33 return (uint16_t)insertlen; 34 } else if (insertlen < 130) { 35 uint32_t nbits = Log2FloorNonZero(insertlen - 2) - 1u; 36 return (uint16_t)((nbits << 1) + ((insertlen - 2) >> nbits) + 2); 37 } else if (insertlen < 2114) { 38 return (uint16_t)(Log2FloorNonZero(insertlen - 66) + 10); 39 } else if (insertlen < 6210) { 40 return 21u; 41 } else if (insertlen < 22594) { 42 return 22u; 43 } else { 44 return 23u; 45 } 46 } 47 48 static BROTLI_INLINE uint16_t GetCopyLengthCode(size_t copylen) { 49 if (copylen < 10) { 50 return (uint16_t)(copylen - 2); 51 } else if (copylen < 134) { 52 uint32_t nbits = Log2FloorNonZero(copylen - 6) - 1u; 53 return (uint16_t)((nbits << 1) + ((copylen - 6) >> nbits) + 4); 54 } else if (copylen < 2118) { 55 return (uint16_t)(Log2FloorNonZero(copylen - 70) + 12); 56 } else { 57 return 23u; 58 } 59 } 60 61 static BROTLI_INLINE uint16_t CombineLengthCodes( 62 uint16_t inscode, uint16_t copycode, BROTLI_BOOL use_last_distance) { 63 uint16_t bits64 = 64 (uint16_t)((copycode & 0x7u) | ((inscode & 0x7u) << 3)); 65 if (use_last_distance && inscode < 8 && copycode < 16) { 66 return (copycode < 8) ? bits64 : (bits64 | 64); 67 } else { 68 /* Specification: 5 Encoding of ... (last table) */ 69 /* offset = 2 * index, where index is in range [0..8] */ 70 int offset = 2 * ((copycode >> 3) + 3 * (inscode >> 3)); 71 /* All values in specification are K * 64, 72 where K = [2, 3, 6, 4, 5, 8, 7, 9, 10], 73 i + 1 = [1, 2, 3, 4, 5, 6, 7, 8, 9], 74 K - i - 1 = [1, 1, 3, 0, 0, 2, 0, 1, 2] = D. 75 All values in D require only 2 bits to encode. 76 Magic constant is shifted 6 bits left, to avoid final multiplication. */ 77 offset = (offset << 5) + 0x40 + ((0x520D40 >> offset) & 0xC0); 78 return (uint16_t)offset | bits64; 79 } 80 } 81 82 static BROTLI_INLINE void GetLengthCode(size_t insertlen, size_t copylen, 83 BROTLI_BOOL use_last_distance, 84 uint16_t* code) { 85 uint16_t inscode = GetInsertLengthCode(insertlen); 86 uint16_t copycode = GetCopyLengthCode(copylen); 87 *code = CombineLengthCodes(inscode, copycode, use_last_distance); 88 } 89 90 static BROTLI_INLINE uint32_t GetInsertBase(uint16_t inscode) { 91 return kInsBase[inscode]; 92 } 93 94 static BROTLI_INLINE uint32_t GetInsertExtra(uint16_t inscode) { 95 return kInsExtra[inscode]; 96 } 97 98 static BROTLI_INLINE uint32_t GetCopyBase(uint16_t copycode) { 99 return kCopyBase[copycode]; 100 } 101 102 static BROTLI_INLINE uint32_t GetCopyExtra(uint16_t copycode) { 103 return kCopyExtra[copycode]; 104 } 105 106 typedef struct Command { 107 uint32_t insert_len_; 108 /* Stores copy_len in low 24 bits and copy_len XOR copy_code in high 8 bit. */ 109 uint32_t copy_len_; 110 uint32_t dist_extra_; 111 uint16_t cmd_prefix_; 112 uint16_t dist_prefix_; 113 } Command; 114 115 /* distance_code is e.g. 0 for same-as-last short code, or 16 for offset 1. */ 116 static BROTLI_INLINE void InitCommand(Command* self, size_t insertlen, 117 size_t copylen, int copylen_code_delta, size_t distance_code) { 118 /* Don't rely on signed int representation, use honest casts. */ 119 uint32_t delta = (uint8_t)((int8_t)copylen_code_delta); 120 self->insert_len_ = (uint32_t)insertlen; 121 self->copy_len_ = (uint32_t)(copylen | (delta << 24)); 122 /* The distance prefix and extra bits are stored in this Command as if 123 npostfix and ndirect were 0, they are only recomputed later after the 124 clustering if needed. */ 125 PrefixEncodeCopyDistance( 126 distance_code, 0, 0, &self->dist_prefix_, &self->dist_extra_); 127 GetLengthCode( 128 insertlen, (size_t)((int)copylen + copylen_code_delta), 129 TO_BROTLI_BOOL(self->dist_prefix_ == 0), &self->cmd_prefix_); 130 } 131 132 static BROTLI_INLINE void InitInsertCommand(Command* self, size_t insertlen) { 133 self->insert_len_ = (uint32_t)insertlen; 134 self->copy_len_ = 4 << 24; 135 self->dist_extra_ = 0; 136 self->dist_prefix_ = BROTLI_NUM_DISTANCE_SHORT_CODES; 137 GetLengthCode(insertlen, 4, BROTLI_FALSE, &self->cmd_prefix_); 138 } 139 140 static BROTLI_INLINE uint32_t CommandRestoreDistanceCode(const Command* self) { 141 if (self->dist_prefix_ < BROTLI_NUM_DISTANCE_SHORT_CODES) { 142 return self->dist_prefix_; 143 } else { 144 uint32_t nbits = self->dist_extra_ >> 24; 145 uint32_t extra = self->dist_extra_ & 0xffffff; 146 /* It is assumed that the distance was first encoded with NPOSTFIX = 0 and 147 NDIRECT = 0, so the code itself is of this form: 148 BROTLI_NUM_DISTANCE_SHORT_CODES + 2 * (nbits - 1) + prefix_bit 149 Therefore, the following expression results in (2 + prefix_bit). */ 150 uint32_t prefix = 151 self->dist_prefix_ + 4u - BROTLI_NUM_DISTANCE_SHORT_CODES - 2u * nbits; 152 /* Subtract 4 for offset (Chapter 4.) and 153 increase by BROTLI_NUM_DISTANCE_SHORT_CODES - 1 */ 154 return (prefix << nbits) + extra + BROTLI_NUM_DISTANCE_SHORT_CODES - 4u; 155 } 156 } 157 158 static BROTLI_INLINE uint32_t CommandDistanceContext(const Command* self) { 159 uint32_t r = self->cmd_prefix_ >> 6; 160 uint32_t c = self->cmd_prefix_ & 7; 161 if ((r == 0 || r == 2 || r == 4 || r == 7) && (c <= 2)) { 162 return c; 163 } 164 return 3; 165 } 166 167 static BROTLI_INLINE uint32_t CommandCopyLen(const Command* self) { 168 return self->copy_len_ & 0xFFFFFF; 169 } 170 171 static BROTLI_INLINE uint32_t CommandCopyLenCode(const Command* self) { 172 int32_t delta = (int8_t)((uint8_t)(self->copy_len_ >> 24)); 173 return (uint32_t)((int32_t)(self->copy_len_ & 0xFFFFFF) + delta); 174 } 175 176 #if defined(__cplusplus) || defined(c_plusplus) 177 } /* extern "C" */ 178 #endif 179 180 #endif /* BROTLI_ENC_COMMAND_H_ */ 181
