entropy_coder.cc (1991B)
1 // Copyright (c) the JPEG XL Project Authors. All rights reserved. 2 // 3 // Use of this source code is governed by a BSD-style 4 // license that can be found in the LICENSE file. 5 6 #include "lib/jxl/entropy_coder.h" 7 8 #include <jxl/memory_manager.h> 9 10 #include <cstdint> 11 #include <vector> 12 13 #include "lib/jxl/ac_context.h" 14 #include "lib/jxl/base/compiler_specific.h" 15 #include "lib/jxl/base/status.h" 16 #include "lib/jxl/coeff_order.h" 17 #include "lib/jxl/coeff_order_fwd.h" 18 #include "lib/jxl/dec_bit_reader.h" 19 #include "lib/jxl/dec_context_map.h" 20 #include "lib/jxl/fields.h" 21 #include "lib/jxl/pack_signed.h" 22 23 namespace jxl { 24 25 Status DecodeBlockCtxMap(JxlMemoryManager* memory_manager, BitReader* br, 26 BlockCtxMap* block_ctx_map) { 27 auto& dct = block_ctx_map->dc_thresholds; 28 auto& qft = block_ctx_map->qf_thresholds; 29 auto& ctx_map = block_ctx_map->ctx_map; 30 bool is_default = static_cast<bool>(br->ReadFixedBits<1>()); 31 if (is_default) { 32 *block_ctx_map = BlockCtxMap(); 33 return true; 34 } 35 block_ctx_map->num_dc_ctxs = 1; 36 for (int j : {0, 1, 2}) { 37 dct[j].resize(br->ReadFixedBits<4>()); 38 block_ctx_map->num_dc_ctxs *= dct[j].size() + 1; 39 for (int& i : dct[j]) { 40 i = UnpackSigned(U32Coder::Read(kDCThresholdDist, br)); 41 } 42 } 43 qft.resize(br->ReadFixedBits<4>()); 44 for (uint32_t& i : qft) { 45 i = U32Coder::Read(kQFThresholdDist, br) + 1; 46 } 47 48 if (block_ctx_map->num_dc_ctxs * (qft.size() + 1) > 64) { 49 return JXL_FAILURE("Invalid block context map: too big"); 50 } 51 52 ctx_map.resize(3 * kNumOrders * block_ctx_map->num_dc_ctxs * 53 (qft.size() + 1)); 54 JXL_RETURN_IF_ERROR( 55 DecodeContextMap(memory_manager, &ctx_map, &block_ctx_map->num_ctxs, br)); 56 if (block_ctx_map->num_ctxs > 16) { 57 return JXL_FAILURE("Invalid block context map: too many distinct contexts"); 58 } 59 return true; 60 } 61 62 #if JXL_CXX_LANG < JXL_CXX_17 63 constexpr uint8_t BlockCtxMap::kDefaultCtxMap[]; // from ac_context.h 64 #endif 65 66 } // namespace jxl