1*2940b44dSPeter Avalos /////////////////////////////////////////////////////////////////////////////// 2*2940b44dSPeter Avalos // 3*2940b44dSPeter Avalos /// \file range_common.h 4*2940b44dSPeter Avalos /// \brief Common things for range encoder and decoder 5*2940b44dSPeter Avalos /// 6*2940b44dSPeter Avalos // Authors: Igor Pavlov 7*2940b44dSPeter Avalos // Lasse Collin 8*2940b44dSPeter Avalos // 9*2940b44dSPeter Avalos // This file has been put into the public domain. 10*2940b44dSPeter Avalos // You can do whatever you want with this file. 11*2940b44dSPeter Avalos // 12*2940b44dSPeter Avalos /////////////////////////////////////////////////////////////////////////////// 13*2940b44dSPeter Avalos 14*2940b44dSPeter Avalos #ifndef LZMA_RANGE_COMMON_H 15*2940b44dSPeter Avalos #define LZMA_RANGE_COMMON_H 16*2940b44dSPeter Avalos 17*2940b44dSPeter Avalos #ifdef HAVE_CONFIG_H 18*2940b44dSPeter Avalos # include "common.h" 19*2940b44dSPeter Avalos #endif 20*2940b44dSPeter Avalos 21*2940b44dSPeter Avalos 22*2940b44dSPeter Avalos /////////////// 23*2940b44dSPeter Avalos // Constants // 24*2940b44dSPeter Avalos /////////////// 25*2940b44dSPeter Avalos 26*2940b44dSPeter Avalos #define RC_SHIFT_BITS 8 27*2940b44dSPeter Avalos #define RC_TOP_BITS 24 28*2940b44dSPeter Avalos #define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS) 29*2940b44dSPeter Avalos #define RC_BIT_MODEL_TOTAL_BITS 11 30*2940b44dSPeter Avalos #define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS) 31*2940b44dSPeter Avalos #define RC_MOVE_BITS 5 32*2940b44dSPeter Avalos 33*2940b44dSPeter Avalos 34*2940b44dSPeter Avalos //////////// 35*2940b44dSPeter Avalos // Macros // 36*2940b44dSPeter Avalos //////////// 37*2940b44dSPeter Avalos 38*2940b44dSPeter Avalos // Resets the probability so that both 0 and 1 have probability of 50 % 39*2940b44dSPeter Avalos #define bit_reset(prob) \ 40*2940b44dSPeter Avalos prob = RC_BIT_MODEL_TOTAL >> 1 41*2940b44dSPeter Avalos 42*2940b44dSPeter Avalos // This does the same for a complete bit tree. 43*2940b44dSPeter Avalos // (A tree represented as an array.) 44*2940b44dSPeter Avalos #define bittree_reset(probs, bit_levels) \ 45*2940b44dSPeter Avalos for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \ 46*2940b44dSPeter Avalos bit_reset((probs)[bt_i]) 47*2940b44dSPeter Avalos 48*2940b44dSPeter Avalos 49*2940b44dSPeter Avalos ////////////////////// 50*2940b44dSPeter Avalos // Type definitions // 51*2940b44dSPeter Avalos ////////////////////// 52*2940b44dSPeter Avalos 53*2940b44dSPeter Avalos /// \brief Type of probabilities used with range coder 54*2940b44dSPeter Avalos /// 55*2940b44dSPeter Avalos /// This needs to be at least 12-bit integer, so uint16_t is a logical choice. 56*2940b44dSPeter Avalos /// However, on some architecture and compiler combinations, a bigger type 57*2940b44dSPeter Avalos /// may give better speed, because the probability variables are accessed 58*2940b44dSPeter Avalos /// a lot. On the other hand, bigger probability type increases cache 59*2940b44dSPeter Avalos /// footprint, since there are 2 to 14 thousand probability variables in 60*2940b44dSPeter Avalos /// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there 61*2940b44dSPeter Avalos /// would be about 1.5 million variables). 62*2940b44dSPeter Avalos /// 63*2940b44dSPeter Avalos /// With malicious files, the initialization speed of the LZMA decoder can 64*2940b44dSPeter Avalos /// become important. In that case, smaller probability variables mean that 65*2940b44dSPeter Avalos /// there is less bytes to write to RAM, which makes initialization faster. 66*2940b44dSPeter Avalos /// With big probability type, the initialization can become so slow that it 67*2940b44dSPeter Avalos /// can be a problem e.g. for email servers doing virus scanning. 68*2940b44dSPeter Avalos /// 69*2940b44dSPeter Avalos /// I will be sticking to uint16_t unless some specific architectures 70*2940b44dSPeter Avalos /// are *much* faster (20-50 %) with uint32_t. 71*2940b44dSPeter Avalos typedef uint16_t probability; 72*2940b44dSPeter Avalos 73*2940b44dSPeter Avalos #endif 74