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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-03-09 13:19:48 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-03-09 13:20:02 +0000 |
commit | 58daab21cd043e1dc37024a7f99b396788372918 (patch) | |
tree | 96771e43bb69f7c1c2b0b4f7374cb74d7866d0cb /web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc | |
parent | Releasing debian version 1.43.2-1. (diff) | |
download | netdata-58daab21cd043e1dc37024a7f99b396788372918.tar.xz netdata-58daab21cd043e1dc37024a7f99b396788372918.zip |
Merging upstream version 1.44.3.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc')
-rw-r--r-- | web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc b/web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc new file mode 100644 index 000000000..e13eedc9d --- /dev/null +++ b/web/server/h2o/libh2o/deps/brotli/enc/literal_cost.cc @@ -0,0 +1,165 @@ +/* Copyright 2013 Google Inc. All Rights Reserved. + + Distributed under MIT license. + See file LICENSE for detail or copy at https://opensource.org/licenses/MIT +*/ + +// Literal cost model to allow backward reference replacement to be efficient. + +#include "./literal_cost.h" + +#include <math.h> +#include <algorithm> + +#include "./fast_log.h" +#include "./types.h" +#include "./utf8_util.h" + +namespace brotli { + +static size_t UTF8Position(size_t last, size_t c, size_t clamp) { + if (c < 128) { + return 0; // Next one is the 'Byte 1' again. + } else if (c >= 192) { // Next one is the 'Byte 2' of utf-8 encoding. + return std::min<size_t>(1, clamp); + } else { + // Let's decide over the last byte if this ends the sequence. + if (last < 0xe0) { + return 0; // Completed two or three byte coding. + } else { // Next one is the 'Byte 3' of utf-8 encoding. + return std::min<size_t>(2, clamp); + } + } +} + +static size_t DecideMultiByteStatsLevel(size_t pos, size_t len, size_t mask, + const uint8_t *data) { + size_t counts[3] = { 0 }; + size_t max_utf8 = 1; // should be 2, but 1 compresses better. + size_t last_c = 0; + size_t utf8_pos = 0; + for (size_t i = 0; i < len; ++i) { + size_t c = data[(pos + i) & mask]; + utf8_pos = UTF8Position(last_c, c, 2); + ++counts[utf8_pos]; + last_c = c; + } + if (counts[2] < 500) { + max_utf8 = 1; + } + if (counts[1] + counts[2] < 25) { + max_utf8 = 0; + } + return max_utf8; +} + +void EstimateBitCostsForLiteralsUTF8(size_t pos, size_t len, size_t mask, + const uint8_t *data, float *cost) { + + // max_utf8 is 0 (normal ascii single byte modeling), + // 1 (for 2-byte utf-8 modeling), or 2 (for 3-byte utf-8 modeling). + const size_t max_utf8 = DecideMultiByteStatsLevel(pos, len, mask, data); + size_t histogram[3][256] = { { 0 } }; + size_t window_half = 495; + size_t in_window = std::min(window_half, len); + size_t in_window_utf8[3] = { 0 }; + + // Bootstrap histograms. + size_t last_c = 0; + size_t utf8_pos = 0; + for (size_t i = 0; i < in_window; ++i) { + size_t c = data[(pos + i) & mask]; + ++histogram[utf8_pos][c]; + ++in_window_utf8[utf8_pos]; + utf8_pos = UTF8Position(last_c, c, max_utf8); + last_c = c; + } + + // Compute bit costs with sliding window. + for (size_t i = 0; i < len; ++i) { + if (i >= window_half) { + // Remove a byte in the past. + size_t c = i < window_half + 1 ? + 0 : data[(pos + i - window_half - 1) & mask]; + size_t last_c = i < window_half + 2 ? + 0 : data[(pos + i - window_half - 2) & mask]; + size_t utf8_pos2 = UTF8Position(last_c, c, max_utf8); + --histogram[utf8_pos2][data[(pos + i - window_half) & mask]]; + --in_window_utf8[utf8_pos2]; + } + if (i + window_half < len) { + // Add a byte in the future. + size_t c = data[(pos + i + window_half - 1) & mask]; + size_t last_c = data[(pos + i + window_half - 2) & mask]; + size_t utf8_pos2 = UTF8Position(last_c, c, max_utf8); + ++histogram[utf8_pos2][data[(pos + i + window_half) & mask]]; + ++in_window_utf8[utf8_pos2]; + } + size_t c = i < 1 ? 0 : data[(pos + i - 1) & mask]; + size_t last_c = i < 2 ? 0 : data[(pos + i - 2) & mask]; + size_t utf8_pos = UTF8Position(last_c, c, max_utf8); + size_t masked_pos = (pos + i) & mask; + size_t histo = histogram[utf8_pos][data[masked_pos]]; + if (histo == 0) { + histo = 1; + } + double lit_cost = FastLog2(in_window_utf8[utf8_pos]) - FastLog2(histo); + lit_cost += 0.02905; + if (lit_cost < 1.0) { + lit_cost *= 0.5; + lit_cost += 0.5; + } + // Make the first bytes more expensive -- seems to help, not sure why. + // Perhaps because the entropy source is changing its properties + // rapidly in the beginning of the file, perhaps because the beginning + // of the data is a statistical "anomaly". + if (i < 2000) { + lit_cost += 0.7 - (static_cast<double>(2000 - i) / 2000.0 * 0.35); + } + cost[i] = static_cast<float>(lit_cost); + } +} + +void EstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask, + const uint8_t *data, float *cost) { + if (IsMostlyUTF8(data, pos, mask, len, kMinUTF8Ratio)) { + EstimateBitCostsForLiteralsUTF8(pos, len, mask, data, cost); + return; + } + size_t histogram[256] = { 0 }; + size_t window_half = 2000; + size_t in_window = std::min(window_half, len); + + // Bootstrap histogram. + for (size_t i = 0; i < in_window; ++i) { + ++histogram[data[(pos + i) & mask]]; + } + + // Compute bit costs with sliding window. + for (size_t i = 0; i < len; ++i) { + if (i >= window_half) { + // Remove a byte in the past. + --histogram[data[(pos + i - window_half) & mask]]; + --in_window; + } + if (i + window_half < len) { + // Add a byte in the future. + ++histogram[data[(pos + i + window_half) & mask]]; + ++in_window; + } + size_t histo = histogram[data[(pos + i) & mask]]; + if (histo == 0) { + histo = 1; + } + double lit_cost = FastLog2(in_window) - FastLog2(histo); + lit_cost += 0.029; + if (lit_cost < 1.0) { + lit_cost *= 0.5; + lit_cost += 0.5; + } + cost[i] = static_cast<float>(lit_cost); + } +} + + +} // namespace brotli |