1/* ******************************************************************
2 * hist : Histogram functions
3 * part of Finite State Entropy project
4 * Copyright (c) Yann Collet, Facebook, Inc.
5 *
6 * You can contact the author at :
7 * - FSE source repository : https://github.com/Cyan4973/FiniteStateEntropy
8 * - Public forum : https://groups.google.com/forum/#!forum/lz4c
9 *
10 * This source code is licensed under both the BSD-style license (found in the
11 * LICENSE file in the root directory of this source tree) and the GPLv2 (found
12 * in the COPYING file in the root directory of this source tree).
13 * You may select, at your option, one of the above-listed licenses.
14****************************************************************** */
15
16/* --- dependencies --- */
17#include "../common/zstd_deps.h" /* size_t */
18
19
20/* --- simple histogram functions --- */
21
22/*! HIST_count():
23 * Provides the precise count of each byte within a table 'count'.
24 * 'count' is a table of unsigned int, of minimum size (*maxSymbolValuePtr+1).
25 * Updates *maxSymbolValuePtr with actual largest symbol value detected.
26 * @return : count of the most frequent symbol (which isn't identified).
27 * or an error code, which can be tested using HIST_isError().
28 * note : if return == srcSize, there is only one symbol.
29 */
30size_t HIST_count(unsigned* count, unsigned* maxSymbolValuePtr,
31 const void* src, size_t srcSize);
32
33unsigned HIST_isError(size_t code); /*< tells if a return value is an error code */
34
35
36/* --- advanced histogram functions --- */
37
38#define HIST_WKSP_SIZE_U32 1024
39#define HIST_WKSP_SIZE (HIST_WKSP_SIZE_U32 * sizeof(unsigned))
40/* HIST_count_wksp() :
41 * Same as HIST_count(), but using an externally provided scratch buffer.
42 * Benefit is this function will use very little stack space.
43 * `workSpace` is a writable buffer which must be 4-bytes aligned,
44 * `workSpaceSize` must be >= HIST_WKSP_SIZE
45 */
46size_t HIST_count_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
47 const void* src, size_t srcSize,
48 void* workSpace, size_t workSpaceSize);
49
50/* HIST_countFast() :
51 * same as HIST_count(), but blindly trusts that all byte values within src are <= *maxSymbolValuePtr.
52 * This function is unsafe, and will segfault if any value within `src` is `> *maxSymbolValuePtr`
53 */
54size_t HIST_countFast(unsigned* count, unsigned* maxSymbolValuePtr,
55 const void* src, size_t srcSize);
56
57/* HIST_countFast_wksp() :
58 * Same as HIST_countFast(), but using an externally provided scratch buffer.
59 * `workSpace` is a writable buffer which must be 4-bytes aligned,
60 * `workSpaceSize` must be >= HIST_WKSP_SIZE
61 */
62size_t HIST_countFast_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
63 const void* src, size_t srcSize,
64 void* workSpace, size_t workSpaceSize);
65
66/*! HIST_count_simple() :
67 * Same as HIST_countFast(), this function is unsafe,
68 * and will segfault if any value within `src` is `> *maxSymbolValuePtr`.
69 * It is also a bit slower for large inputs.
70 * However, it does not need any additional memory (not even on stack).
71 * @return : count of the most frequent symbol.
72 * Note this function doesn't produce any error (i.e. it must succeed).
73 */
74unsigned HIST_count_simple(unsigned* count, unsigned* maxSymbolValuePtr,
75 const void* src, size_t srcSize);
76

source code of linux/lib/zstd/compress/hist.h