1 // SPDX-License-Identifier: 0BSD 2 3 /////////////////////////////////////////////////////////////////////////////// 4 // 5 /// \file range_common.h 6 /// \brief Common things for range encoder and decoder 7 /// 8 // Authors: Igor Pavlov 9 // Lasse Collin 10 // 11 /////////////////////////////////////////////////////////////////////////////// 12 13 #ifndef LZMA_RANGE_COMMON_H 14 #define LZMA_RANGE_COMMON_H 15 16 // Skip common.h if building price_tablegen.c. 17 #ifndef BUILDING_PRICE_TABLEGEN 18 # include "common.h" 19 #endif 20 21 22 /////////////// 23 // Constants // 24 /////////////// 25 26 #define RC_SHIFT_BITS 8 27 #define RC_TOP_BITS 24 28 #define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS) 29 #define RC_BIT_MODEL_TOTAL_BITS 11 30 #define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS) 31 #define RC_MOVE_BITS 5 32 33 34 //////////// 35 // Macros // 36 //////////// 37 38 // Resets the probability so that both 0 and 1 have probability of 50 % 39 #define bit_reset(prob) \ 40 prob = RC_BIT_MODEL_TOTAL >> 1 41 42 // This does the same for a complete bit tree. 43 // (A tree represented as an array.) 44 #define bittree_reset(probs, bit_levels) \ 45 for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \ 46 bit_reset((probs)[bt_i]) 47 48 49 ////////////////////// 50 // Type definitions // 51 ////////////////////// 52 53 /// \brief Type of probabilities used with range coder 54 /// 55 /// This needs to be at least 12-bit integer, so uint16_t is a logical choice. 56 /// However, on some architecture and compiler combinations, a bigger type 57 /// may give better speed, because the probability variables are accessed 58 /// a lot. On the other hand, bigger probability type increases cache 59 /// footprint, since there are 2 to 14 thousand probability variables in 60 /// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there 61 /// would be about 1.5 million variables). 62 /// 63 /// With malicious files, the initialization speed of the LZMA decoder can 64 /// become important. In that case, smaller probability variables mean that 65 /// there is less bytes to write to RAM, which makes initialization faster. 66 /// With big probability type, the initialization can become so slow that it 67 /// can be a problem e.g. for email servers doing virus scanning. 68 /// 69 /// I will be sticking to uint16_t unless some specific architectures 70 /// are *much* faster (20-50 %) with uint32_t. 71 /// 72 /// Update in 2024: The branchless C and x86-64 assembly was written so that 73 /// probability is assumed to be uint16_t. (In contrast, LZMA SDK 23.01 74 /// assembly supports both types.) 75 typedef uint16_t probability; 76 77 #endif 78
Indexes created Sat Sep 12 00:25:55 UTC 2026