1*4d1abfb2Sjoerg /////////////////////////////////////////////////////////////////////////////// 2*4d1abfb2Sjoerg // 3*4d1abfb2Sjoerg /// \file range_common.h 4*4d1abfb2Sjoerg /// \brief Common things for range encoder and decoder 5*4d1abfb2Sjoerg /// 6*4d1abfb2Sjoerg // Authors: Igor Pavlov 7*4d1abfb2Sjoerg // Lasse Collin 8*4d1abfb2Sjoerg // 9*4d1abfb2Sjoerg // This file has been put into the public domain. 10*4d1abfb2Sjoerg // You can do whatever you want with this file. 11*4d1abfb2Sjoerg // 12*4d1abfb2Sjoerg /////////////////////////////////////////////////////////////////////////////// 13*4d1abfb2Sjoerg 14*4d1abfb2Sjoerg #ifndef LZMA_RANGE_COMMON_H 15*4d1abfb2Sjoerg #define LZMA_RANGE_COMMON_H 16*4d1abfb2Sjoerg 17*4d1abfb2Sjoerg #include "common.h" 18*4d1abfb2Sjoerg 19*4d1abfb2Sjoerg 20*4d1abfb2Sjoerg /////////////// 21*4d1abfb2Sjoerg // Constants // 22*4d1abfb2Sjoerg /////////////// 23*4d1abfb2Sjoerg 24*4d1abfb2Sjoerg #define RC_SHIFT_BITS 8 25*4d1abfb2Sjoerg #define RC_TOP_BITS 24 26*4d1abfb2Sjoerg #define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS) 27*4d1abfb2Sjoerg #define RC_BIT_MODEL_TOTAL_BITS 11 28*4d1abfb2Sjoerg #define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS) 29*4d1abfb2Sjoerg #define RC_MOVE_BITS 5 30*4d1abfb2Sjoerg 31*4d1abfb2Sjoerg 32*4d1abfb2Sjoerg //////////// 33*4d1abfb2Sjoerg // Macros // 34*4d1abfb2Sjoerg //////////// 35*4d1abfb2Sjoerg 36*4d1abfb2Sjoerg // Resets the probability so that both 0 and 1 have probability of 50 % 37*4d1abfb2Sjoerg #define bit_reset(prob) \ 38*4d1abfb2Sjoerg prob = RC_BIT_MODEL_TOTAL >> 1 39*4d1abfb2Sjoerg 40*4d1abfb2Sjoerg // This does the same for a complete bit tree. 41*4d1abfb2Sjoerg // (A tree represented as an array.) 42*4d1abfb2Sjoerg #define bittree_reset(probs, bit_levels) \ 43*4d1abfb2Sjoerg for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \ 44*4d1abfb2Sjoerg bit_reset((probs)[bt_i]) 45*4d1abfb2Sjoerg 46*4d1abfb2Sjoerg 47*4d1abfb2Sjoerg ////////////////////// 48*4d1abfb2Sjoerg // Type definitions // 49*4d1abfb2Sjoerg ////////////////////// 50*4d1abfb2Sjoerg 51*4d1abfb2Sjoerg /// \brief Type of probabilities used with range coder 52*4d1abfb2Sjoerg /// 53*4d1abfb2Sjoerg /// This needs to be at least 12-bit integer, so uint16_t is a logical choice. 54*4d1abfb2Sjoerg /// However, on some architecture and compiler combinations, a bigger type 55*4d1abfb2Sjoerg /// may give better speed, because the probability variables are accessed 56*4d1abfb2Sjoerg /// a lot. On the other hand, bigger probability type increases cache 57*4d1abfb2Sjoerg /// footprint, since there are 2 to 14 thousand probability variables in 58*4d1abfb2Sjoerg /// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there 59*4d1abfb2Sjoerg /// would be about 1.5 million variables). 60*4d1abfb2Sjoerg /// 61*4d1abfb2Sjoerg /// With malicious files, the initialization speed of the LZMA decoder can 62*4d1abfb2Sjoerg /// become important. In that case, smaller probability variables mean that 63*4d1abfb2Sjoerg /// there is less bytes to write to RAM, which makes initialization faster. 64*4d1abfb2Sjoerg /// With big probability type, the initialization can become so slow that it 65*4d1abfb2Sjoerg /// can be a problem e.g. for email servers doing virus scanning. 66*4d1abfb2Sjoerg /// 67*4d1abfb2Sjoerg /// I will be sticking to uint16_t unless some specific architectures 68*4d1abfb2Sjoerg /// are *much* faster (20-50 %) with uint32_t. 69*4d1abfb2Sjoerg typedef uint16_t probability; 70*4d1abfb2Sjoerg 71*4d1abfb2Sjoerg #endif 72