1 files changed, 66 insertions, 0 deletions
diff --git a/modules/brotli/enc/fast_log.h b/modules/brotli/enc/fast_log.h
new file mode 100644
index 0000000000..2094f13e55
--- /dev/null
+++ b/modules/brotli/enc/fast_log.h
@@ -0,0 +1,66 @@
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* Utilities for fast computation of logarithms. */
+
+#ifndef BROTLI_ENC_FAST_LOG_H_
+#define BROTLI_ENC_FAST_LOG_H_
+
+#include <math.h>
+
+#include "../common/platform.h"
+#include <brotli/types.h>
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+static BROTLI_INLINE uint32_t Log2FloorNonZero(size_t n) {
+#if defined(BROTLI_BSR32)
+  return BROTLI_BSR32((uint32_t)n);
+#else
+  uint32_t result = 0;
+  while (n >>= 1) result++;
+  return result;
+#endif
+}
+
+#define BROTLI_LOG2_TABLE_SIZE 256
+
+/* A lookup table for small values of log2(int) to be used in entropy
+   computation. */
+BROTLI_INTERNAL extern const double kBrotliLog2Table[BROTLI_LOG2_TABLE_SIZE];
+
+/* Visual Studio 2012 and Android API levels < 18 do not have the log2()
+ * function defined, so we use log() and a multiplication instead. */
+#if !defined(BROTLI_HAVE_LOG2)
+#if ((defined(_MSC_VER) && _MSC_VER <= 1700) || \
+     (defined(__ANDROID_API__) && __ANDROID_API__ < 18))
+#define BROTLI_HAVE_LOG2 0
+#else
+#define BROTLI_HAVE_LOG2 1
+#endif
+#endif
+
+#define LOG_2_INV 1.4426950408889634
+
+/* Faster logarithm for small integers, with the property of log2(0) == 0. */
+static BROTLI_INLINE double FastLog2(size_t v) {
+  if (v < BROTLI_LOG2_TABLE_SIZE) {
+    return kBrotliLog2Table[v];
+  }
+#if !(BROTLI_HAVE_LOG2)
+  return log((double)v) * LOG_2_INV;
+#else
+  return log2((double)v);
+#endif
+}
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}  /* extern "C" */
+#endif
+
+#endif  /* BROTLI_ENC_FAST_LOG_H_ */