Index: third_party/brotli/enc/literal_cost.cc |
diff --git a/third_party/brotli/enc/literal_cost.cc b/third_party/brotli/enc/literal_cost.cc |
deleted file mode 100644 |
index e6be86fc64ea0d85032511663d3d4a056245b545..0000000000000000000000000000000000000000 |
--- a/third_party/brotli/enc/literal_cost.cc |
+++ /dev/null |
@@ -1,165 +0,0 @@ |
-/* 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; |
-} |
- |
-static 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 |