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-rw-r--r--modules/brotli/enc/literal_cost.c175
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diff --git a/modules/brotli/enc/literal_cost.c b/modules/brotli/enc/literal_cost.c
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+/* 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 "../common/platform.h"
+#include <brotli/types.h>
+#include "./fast_log.h"
+#include "./utf8_util.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+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 BROTLI_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 BROTLI_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 i;
+ for (i = 0; i < len; ++i) {
+ size_t c = data[(pos + i) & mask];
+ ++counts[UTF8Position(last_c, c, 2)];
+ 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 = BROTLI_MIN(size_t, window_half, len);
+ size_t in_window_utf8[3] = { 0 };
+
+ size_t i;
+ { /* Bootstrap histograms. */
+ size_t last_c = 0;
+ size_t utf8_pos = 0;
+ for (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 (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]];
+ double lit_cost;
+ if (histo == 0) {
+ histo = 1;
+ }
+ 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 - ((double)(2000 - i) / 2000.0 * 0.35);
+ }
+ cost[i] = (float)lit_cost;
+ }
+ }
+}
+
+void BrotliEstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask,
+ const uint8_t* data, float* cost) {
+ if (BrotliIsMostlyUTF8(data, pos, mask, len, kMinUTF8Ratio)) {
+ EstimateBitCostsForLiteralsUTF8(pos, len, mask, data, cost);
+ return;
+ } else {
+ size_t histogram[256] = { 0 };
+ size_t window_half = 2000;
+ size_t in_window = BROTLI_MIN(size_t, window_half, len);
+
+ /* Bootstrap histogram. */
+ size_t i;
+ for (i = 0; i < in_window; ++i) {
+ ++histogram[data[(pos + i) & mask]];
+ }
+
+ /* Compute bit costs with sliding window. */
+ for (i = 0; i < len; ++i) {
+ size_t histo;
+ 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;
+ }
+ 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] = (float)lit_cost;
+ }
+ }
+ }
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+} /* extern "C" */
+#endif