186229Stmm/////////////////////////////////////////////////////////////////////////////// 286229Stmm// 386229Stmm/// \file range_common.h 486229Stmm/// \brief Common things for range encoder and decoder 586229Stmm/// 686229Stmm// Authors: Igor Pavlov 786229Stmm// Lasse Collin 886229Stmm// 986229Stmm// This file has been put into the public domain. 1086229Stmm// You can do whatever you want with this file. 1186229Stmm// 1286229Stmm/////////////////////////////////////////////////////////////////////////////// 1386229Stmm 1486229Stmm#ifndef LZMA_RANGE_COMMON_H 1586229Stmm#define LZMA_RANGE_COMMON_H 1686229Stmm 1786229Stmm#ifdef HAVE_CONFIG_H 1886229Stmm# include "common.h" 1986229Stmm#endif 2086229Stmm 2186229Stmm 2286229Stmm/////////////// 2386229Stmm// Constants // 2486229Stmm/////////////// 2586229Stmm 2686229Stmm#define RC_SHIFT_BITS 8 2786229Stmm#define RC_TOP_BITS 24 2886229Stmm#define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS) 2986229Stmm#define RC_BIT_MODEL_TOTAL_BITS 11 3086229Stmm#define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS) 3186229Stmm#define RC_MOVE_BITS 5 32186347Snwhitehorn 33186347Snwhitehorn 3486229Stmm//////////// 35186347Snwhitehorn// Macros // 36186347Snwhitehorn//////////// 37141753Smarius 38119697Smarcel// Resets the probability so that both 0 and 1 have probability of 50 % 39207243Smarius#define bit_reset(prob) \ 40230632Smarius prob = RC_BIT_MODEL_TOTAL >> 1 41230632Smarius 42186347Snwhitehorn// This does the same for a complete bit tree. 43230632Smarius// (A tree represented as an array.) 4486229Stmm#define bittree_reset(probs, bit_levels) \ 4586229Stmm 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. 71typedef uint16_t probability; 72 73#endif 74