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Diffstat (limited to 'third_party/jpeg-xl/lib/jxl/ac_context.h')
| -rw-r--r-- | third_party/jpeg-xl/lib/jxl/ac_context.h | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/third_party/jpeg-xl/lib/jxl/ac_context.h b/third_party/jpeg-xl/lib/jxl/ac_context.h new file mode 100644 index 0000000000..a2b9e046d1 --- /dev/null +++ b/third_party/jpeg-xl/lib/jxl/ac_context.h @@ -0,0 +1,149 @@ +// Copyright (c) the JPEG XL Project Authors. All rights reserved. +// +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +#ifndef LIB_JXL_AC_CONTEXT_H_ +#define LIB_JXL_AC_CONTEXT_H_ + +#include <algorithm> +#include <vector> + +#include "lib/jxl/base/bits.h" +#include "lib/jxl/base/status.h" +#include "lib/jxl/coeff_order_fwd.h" + +namespace jxl { + +// Block context used for scanning order, number of non-zeros, AC coefficients. +// Equal to the channel. +constexpr uint32_t kDCTOrderContextStart = 0; + +// The number of predicted nonzeros goes from 0 to 1008. We use +// ceil(log2(predicted+1)) as a context for the number of nonzeros, so from 0 to +// 10, inclusive. +constexpr uint32_t kNonZeroBuckets = 37; + +static const uint16_t kCoeffFreqContext[64] = { + 0xBAD, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, + 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, + 23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, + 27, 27, 27, 27, 28, 28, 28, 28, 29, 29, 29, 29, 30, 30, 30, 30, +}; + +static const uint16_t kCoeffNumNonzeroContext[64] = { + 0xBAD, 0, 31, 62, 62, 93, 93, 93, 93, 123, 123, 123, 123, + 152, 152, 152, 152, 152, 152, 152, 152, 180, 180, 180, 180, 180, + 180, 180, 180, 180, 180, 180, 180, 206, 206, 206, 206, 206, 206, + 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, + 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, +}; + +// Supremum of ZeroDensityContext(x, y) + 1, when x + y < 64. +constexpr int kZeroDensityContextCount = 458; +// Supremum of ZeroDensityContext(x, y) + 1. +constexpr int kZeroDensityContextLimit = 474; + +/* This function is used for entropy-sources pre-clustering. + * + * Ideally, each combination of |nonzeros_left| and |k| should go to its own + * bucket; but it implies (64 * 63 / 2) == 2016 buckets. If there is other + * dimension (e.g. block context), then number of primary clusters becomes too + * big. + * + * To solve this problem, |nonzeros_left| and |k| values are clustered. It is + * known that their sum is at most 64, consequently, the total number buckets + * is at most A(64) * B(64). + */ +// TODO(user): investigate, why disabling pre-clustering makes entropy code +// less dense. Perhaps we would need to add HQ clustering algorithm that would +// be able to squeeze better by spending more CPU cycles. +static JXL_INLINE size_t ZeroDensityContext(size_t nonzeros_left, size_t k, + size_t covered_blocks, + size_t log2_covered_blocks, + size_t prev) { + JXL_DASSERT((1u << log2_covered_blocks) == covered_blocks); + nonzeros_left = (nonzeros_left + covered_blocks - 1) >> log2_covered_blocks; + k >>= log2_covered_blocks; + JXL_DASSERT(k > 0); + JXL_DASSERT(k < 64); + JXL_DASSERT(nonzeros_left > 0); + // Asserting nonzeros_left + k < 65 here causes crashes in debug mode with + // invalid input, since the (hot) decoding loop does not check this condition. + // As no out-of-bound memory reads are issued even if that condition is + // broken, we check this simpler condition which holds anyway. The decoder + // will still mark a file in which that condition happens as not valid at the + // end of the decoding loop, as `nzeros` will not be `0`. + JXL_DASSERT(nonzeros_left < 64); + return (kCoeffNumNonzeroContext[nonzeros_left] + kCoeffFreqContext[k]) * 2 + + prev; +} + +struct BlockCtxMap { + std::vector<int> dc_thresholds[3]; + std::vector<uint32_t> qf_thresholds; + std::vector<uint8_t> ctx_map; + size_t num_ctxs, num_dc_ctxs; + + static constexpr uint8_t kDefaultCtxMap[] = { + // Default ctx map clusters all the large transforms together. + 0, 1, 2, 2, 3, 3, 4, 5, 6, 6, 6, 6, 6, // + 7, 8, 9, 9, 10, 11, 12, 13, 14, 14, 14, 14, 14, // + 7, 8, 9, 9, 10, 11, 12, 13, 14, 14, 14, 14, 14, // + }; + static_assert(3 * kNumOrders == + sizeof(kDefaultCtxMap) / sizeof *kDefaultCtxMap, + "Update default context map"); + + size_t Context(int dc_idx, uint32_t qf, size_t ord, size_t c) const { + size_t qf_idx = 0; + for (uint32_t t : qf_thresholds) { + if (qf > t) qf_idx++; + } + size_t idx = c < 2 ? c ^ 1 : 2; + idx = idx * kNumOrders + ord; + idx = idx * (qf_thresholds.size() + 1) + qf_idx; + idx = idx * num_dc_ctxs + dc_idx; + return ctx_map[idx]; + } + // Non-zero context is based on number of non-zeros and block context. + // For better clustering, contexts with same number of non-zeros are grouped. + constexpr uint32_t ZeroDensityContextsOffset(uint32_t block_ctx) const { + return num_ctxs * kNonZeroBuckets + kZeroDensityContextCount * block_ctx; + } + + // Context map for AC coefficients consists of 2 blocks: + // |num_ctxs x : context for number of non-zeros in the block + // kNonZeroBuckets| computed from block context and predicted + // value (based top and left values) + // |num_ctxs x : context for AC coefficient symbols, + // kZeroDensityContextCount| computed from block context, + // number of non-zeros left and + // index in scan order + constexpr uint32_t NumACContexts() const { + return num_ctxs * (kNonZeroBuckets + kZeroDensityContextCount); + } + + // Non-zero context is based on number of non-zeros and block context. + // For better clustering, contexts with same number of non-zeros are grouped. + inline uint32_t NonZeroContext(uint32_t non_zeros, uint32_t block_ctx) const { + uint32_t ctx; + if (non_zeros >= 64) non_zeros = 64; + if (non_zeros < 8) { + ctx = non_zeros; + } else { + ctx = 4 + non_zeros / 2; + } + return ctx * num_ctxs + block_ctx; + } + + BlockCtxMap() { + ctx_map.assign(std::begin(kDefaultCtxMap), std::end(kDefaultCtxMap)); + num_ctxs = *std::max_element(ctx_map.begin(), ctx_map.end()) + 1; + num_dc_ctxs = 1; + } +}; + +} // namespace jxl + +#endif // LIB_JXL_AC_CONTEXT_H_ |