1*5a645f22SBen Gras /////////////////////////////////////////////////////////////////////////////// 2*5a645f22SBen Gras // 3*5a645f22SBen Gras /// \file range_common.h 4*5a645f22SBen Gras /// \brief Common things for range encoder and decoder 5*5a645f22SBen Gras /// 6*5a645f22SBen Gras // Authors: Igor Pavlov 7*5a645f22SBen Gras // Lasse Collin 8*5a645f22SBen Gras // 9*5a645f22SBen Gras // This file has been put into the public domain. 10*5a645f22SBen Gras // You can do whatever you want with this file. 11*5a645f22SBen Gras // 12*5a645f22SBen Gras /////////////////////////////////////////////////////////////////////////////// 13*5a645f22SBen Gras 14*5a645f22SBen Gras #ifndef LZMA_RANGE_COMMON_H 15*5a645f22SBen Gras #define LZMA_RANGE_COMMON_H 16*5a645f22SBen Gras 17*5a645f22SBen Gras #ifdef HAVE_CONFIG_H 18*5a645f22SBen Gras # include "common.h" 19*5a645f22SBen Gras #endif 20*5a645f22SBen Gras 21*5a645f22SBen Gras 22*5a645f22SBen Gras /////////////// 23*5a645f22SBen Gras // Constants // 24*5a645f22SBen Gras /////////////// 25*5a645f22SBen Gras 26*5a645f22SBen Gras #define RC_SHIFT_BITS 8 27*5a645f22SBen Gras #define RC_TOP_BITS 24 28*5a645f22SBen Gras #define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS) 29*5a645f22SBen Gras #define RC_BIT_MODEL_TOTAL_BITS 11 30*5a645f22SBen Gras #define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS) 31*5a645f22SBen Gras #define RC_MOVE_BITS 5 32*5a645f22SBen Gras 33*5a645f22SBen Gras 34*5a645f22SBen Gras //////////// 35*5a645f22SBen Gras // Macros // 36*5a645f22SBen Gras //////////// 37*5a645f22SBen Gras 38*5a645f22SBen Gras // Resets the probability so that both 0 and 1 have probability of 50 % 39*5a645f22SBen Gras #define bit_reset(prob) \ 40*5a645f22SBen Gras prob = RC_BIT_MODEL_TOTAL >> 1 41*5a645f22SBen Gras 42*5a645f22SBen Gras // This does the same for a complete bit tree. 43*5a645f22SBen Gras // (A tree represented as an array.) 44*5a645f22SBen Gras #define bittree_reset(probs, bit_levels) \ 45*5a645f22SBen Gras for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \ 46*5a645f22SBen Gras bit_reset((probs)[bt_i]) 47*5a645f22SBen Gras 48*5a645f22SBen Gras 49*5a645f22SBen Gras ////////////////////// 50*5a645f22SBen Gras // Type definitions // 51*5a645f22SBen Gras ////////////////////// 52*5a645f22SBen Gras 53*5a645f22SBen Gras /// \brief Type of probabilities used with range coder 54*5a645f22SBen Gras /// 55*5a645f22SBen Gras /// This needs to be at least 12-bit integer, so uint16_t is a logical choice. 56*5a645f22SBen Gras /// However, on some architecture and compiler combinations, a bigger type 57*5a645f22SBen Gras /// may give better speed, because the probability variables are accessed 58*5a645f22SBen Gras /// a lot. On the other hand, bigger probability type increases cache 59*5a645f22SBen Gras /// footprint, since there are 2 to 14 thousand probability variables in 60*5a645f22SBen Gras /// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there 61*5a645f22SBen Gras /// would be about 1.5 million variables). 62*5a645f22SBen Gras /// 63*5a645f22SBen Gras /// With malicious files, the initialization speed of the LZMA decoder can 64*5a645f22SBen Gras /// become important. In that case, smaller probability variables mean that 65*5a645f22SBen Gras /// there is less bytes to write to RAM, which makes initialization faster. 66*5a645f22SBen Gras /// With big probability type, the initialization can become so slow that it 67*5a645f22SBen Gras /// can be a problem e.g. for email servers doing virus scanning. 68*5a645f22SBen Gras /// 69*5a645f22SBen Gras /// I will be sticking to uint16_t unless some specific architectures 70*5a645f22SBen Gras /// are *much* faster (20-50 %) with uint32_t. 71*5a645f22SBen Gras typedef uint16_t probability; 72*5a645f22SBen Gras 73*5a645f22SBen Gras #endif 74