/* ******************************************************************
* hist : Histogram functions
* part of Finite State Entropy project
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
*  You can contact the author at :
*  - FSE source repository : https://github.com/Cyan4973/FiniteStateEntropy
*  - Public forum : https://groups.google.com/forum/#!forum/lz4c
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
* You may select, at your option, one of the above-listed licenses.
****************************************************************** */

/* --- dependencies --- */
#include "../common/zstd_deps.h"   /* size_t */


/* --- simple histogram functions --- */

/*! HIST_count():
*  Provides the precise count of each byte within a table 'count'.
* 'count' is a table of unsigned int, of minimum size (*maxSymbolValuePtr+1).
*  Updates *maxSymbolValuePtr with actual largest symbol value detected.
* @return : count of the most frequent symbol (which isn't identified).
*           or an error code, which can be tested using HIST_isError().
*           note : if return == srcSize, there is only one symbol.
*/
size_t HIST_count(unsigned* count, unsigned* maxSymbolValuePtr,
                 const void* src, size_t srcSize);

unsigned HIST_isError(size_t code);  /**< tells if a return value is an error code */


/* --- advanced histogram functions --- */

#define HIST_WKSP_SIZE_U32 1024
#define HIST_WKSP_SIZE    (HIST_WKSP_SIZE_U32 * sizeof(unsigned))
/** HIST_count_wksp() :
*  Same as HIST_count(), but using an externally provided scratch buffer.
*  Benefit is this function will use very little stack space.
* `workSpace` is a writable buffer which must be 4-bytes aligned,
* `workSpaceSize` must be >= HIST_WKSP_SIZE
*/
size_t HIST_count_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                      const void* src, size_t srcSize,
                      void* workSpace, size_t workSpaceSize);

/** HIST_countFast() :
*  same as HIST_count(), but blindly trusts that all byte values within src are <= *maxSymbolValuePtr.
*  This function is unsafe, and will segfault if any value within `src` is `> *maxSymbolValuePtr`
*/
size_t HIST_countFast(unsigned* count, unsigned* maxSymbolValuePtr,
                     const void* src, size_t srcSize);

/** HIST_countFast_wksp() :
*  Same as HIST_countFast(), but using an externally provided scratch buffer.
* `workSpace` is a writable buffer which must be 4-bytes aligned,
* `workSpaceSize` must be >= HIST_WKSP_SIZE
*/
size_t HIST_countFast_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
                          const void* src, size_t srcSize,
                          void* workSpace, size_t workSpaceSize);

/*! HIST_count_simple() :
*  Same as HIST_countFast(), this function is unsafe,
*  and will segfault if any value within `src` is `> *maxSymbolValuePtr`.
*  It is also a bit slower for large inputs.
*  However, it does not need any additional memory (not even on stack).
* @return : count of the most frequent symbol.
*  Note this function doesn't produce any error (i.e. it must succeed).
*/
unsigned HIST_count_simple(unsigned* count, unsigned* maxSymbolValuePtr,
                          const void* src, size_t srcSize);