entropy_coder.cc (2049B)
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 <stddef.h> 9 #include <stdint.h> 10 11 #include <algorithm> 12 #include <utility> 13 #include <vector> 14 15 #include "lib/jxl/ac_context.h" 16 #include "lib/jxl/ac_strategy.h" 17 #include "lib/jxl/base/bits.h" 18 #include "lib/jxl/base/compiler_specific.h" 19 #include "lib/jxl/base/status.h" 20 #include "lib/jxl/coeff_order.h" 21 #include "lib/jxl/coeff_order_fwd.h" 22 #include "lib/jxl/dec_ans.h" 23 #include "lib/jxl/dec_bit_reader.h" 24 #include "lib/jxl/dec_context_map.h" 25 #include "lib/jxl/epf.h" 26 #include "lib/jxl/image.h" 27 #include "lib/jxl/image_ops.h" 28 #include "lib/jxl/pack_signed.h" 29 30 namespace jxl { 31 32 Status DecodeBlockCtxMap(BitReader* br, BlockCtxMap* block_ctx_map) { 33 auto& dct = block_ctx_map->dc_thresholds; 34 auto& qft = block_ctx_map->qf_thresholds; 35 auto& ctx_map = block_ctx_map->ctx_map; 36 bool is_default = static_cast<bool>(br->ReadFixedBits<1>()); 37 if (is_default) { 38 *block_ctx_map = BlockCtxMap(); 39 return true; 40 } 41 block_ctx_map->num_dc_ctxs = 1; 42 for (int j : {0, 1, 2}) { 43 dct[j].resize(br->ReadFixedBits<4>()); 44 block_ctx_map->num_dc_ctxs *= dct[j].size() + 1; 45 for (int& i : dct[j]) { 46 i = UnpackSigned(U32Coder::Read(kDCThresholdDist, br)); 47 } 48 } 49 qft.resize(br->ReadFixedBits<4>()); 50 for (uint32_t& i : qft) { 51 i = U32Coder::Read(kQFThresholdDist, br) + 1; 52 } 53 54 if (block_ctx_map->num_dc_ctxs * (qft.size() + 1) > 64) { 55 return JXL_FAILURE("Invalid block context map: too big"); 56 } 57 58 ctx_map.resize(3 * kNumOrders * block_ctx_map->num_dc_ctxs * 59 (qft.size() + 1)); 60 JXL_RETURN_IF_ERROR(DecodeContextMap(&ctx_map, &block_ctx_map->num_ctxs, br)); 61 if (block_ctx_map->num_ctxs > 16) { 62 return JXL_FAILURE("Invalid block context map: too many distinct contexts"); 63 } 64 return true; 65 } 66 67 constexpr uint8_t BlockCtxMap::kDefaultCtxMap[]; // from ac_context.h 68 69 } // namespace jxl