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comparison mupdf-source/thirdparty/brotli/c/enc/fast_log.h @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
1 /* Copyright 2013 Google Inc. All Rights Reserved.
2
3 Distributed under MIT license.
4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
5 */
6
7 /* Utilities for fast computation of logarithms. */
8
9 #ifndef BROTLI_ENC_FAST_LOG_H_
10 #define BROTLI_ENC_FAST_LOG_H_
11
12 #include <math.h>
13
14 #include <brotli/types.h>
15
16 #include "../common/platform.h"
17
18 #if defined(__cplusplus) || defined(c_plusplus)
19 extern "C" {
20 #endif
21
22 static BROTLI_INLINE uint32_t Log2FloorNonZero(size_t n) {
23 #if defined(BROTLI_BSR32)
24 return BROTLI_BSR32((uint32_t)n);
25 #else
26 uint32_t result = 0;
27 while (n >>= 1) result++;
28 return result;
29 #endif
30 }
31
32 #define BROTLI_LOG2_TABLE_SIZE 256
33
34 /* A lookup table for small values of log2(int) to be used in entropy
35 computation. */
36 BROTLI_INTERNAL extern const double kBrotliLog2Table[BROTLI_LOG2_TABLE_SIZE];
37
38 /* Visual Studio 2012 and Android API levels < 18 do not have the log2()
39 * function defined, so we use log() and a multiplication instead. */
40 #if !defined(BROTLI_HAVE_LOG2)
41 #if ((defined(_MSC_VER) && _MSC_VER <= 1700) || \
42 (defined(__ANDROID_API__) && __ANDROID_API__ < 18))
43 #define BROTLI_HAVE_LOG2 0
44 #else
45 #define BROTLI_HAVE_LOG2 1
46 #endif
47 #endif
48
49 #define LOG_2_INV 1.4426950408889634
50
51 /* Faster logarithm for small integers, with the property of log2(0) == 0. */
52 static BROTLI_INLINE double FastLog2(size_t v) {
53 if (v < BROTLI_LOG2_TABLE_SIZE) {
54 return kBrotliLog2Table[v];
55 }
56 #if !(BROTLI_HAVE_LOG2)
57 return log((double)v) * LOG_2_INV;
58 #else
59 return log2((double)v);
60 #endif
61 }
62
63 #if defined(__cplusplus) || defined(c_plusplus)
64 } /* extern "C" */
65 #endif
66
67 #endif /* BROTLI_ENC_FAST_LOG_H_ */