182 lines
7.3 KiB
C
182 lines
7.3 KiB
C
/* ******************************************************************
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* hist : Histogram functions
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* part of Finite State Entropy project
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* You can contact the author at :
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* - FSE source repository : https://github.com/Cyan4973/FiniteStateEntropy
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* - Public forum : https://groups.google.com/forum/#!forum/lz4c
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*
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* This source code is licensed under both the BSD-style license (found in the
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* LICENSE file in the root directory of this source tree) and the GPLv2 (found
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* in the COPYING file in the root directory of this source tree).
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* You may select, at your option, one of the above-listed licenses.
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****************************************************************** */
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/* --- dependencies --- */
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#include "../common/mem.h" /* U32, BYTE, etc. */
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#include "../common/debug.h" /* assert, DEBUGLOG */
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#include "../common/error_private.h" /* ERROR */
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#include "hist.h"
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/* --- Error management --- */
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unsigned HIST_isError(size_t code) { return ERR_isError(code); }
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/*-**************************************************************
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* Histogram functions
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****************************************************************/
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unsigned HIST_count_simple(unsigned* count, unsigned* maxSymbolValuePtr,
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const void* src, size_t srcSize)
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{
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const BYTE* ip = (const BYTE*)src;
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const BYTE* const end = ip + srcSize;
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unsigned maxSymbolValue = *maxSymbolValuePtr;
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unsigned largestCount=0;
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ZSTD_memset(count, 0, (maxSymbolValue+1) * sizeof(*count));
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if (srcSize==0) { *maxSymbolValuePtr = 0; return 0; }
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while (ip<end) {
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assert(*ip <= maxSymbolValue);
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count[*ip++]++;
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}
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while (!count[maxSymbolValue]) maxSymbolValue--;
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*maxSymbolValuePtr = maxSymbolValue;
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{ U32 s;
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for (s=0; s<=maxSymbolValue; s++)
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if (count[s] > largestCount) largestCount = count[s];
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}
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return largestCount;
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}
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typedef enum { trustInput, checkMaxSymbolValue } HIST_checkInput_e;
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/* HIST_count_parallel_wksp() :
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* store histogram into 4 intermediate tables, recombined at the end.
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* this design makes better use of OoO cpus,
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* and is noticeably faster when some values are heavily repeated.
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* But it needs some additional workspace for intermediate tables.
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* `workSpace` must be a U32 table of size >= HIST_WKSP_SIZE_U32.
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* @return : largest histogram frequency,
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* or an error code (notably when histogram's alphabet is larger than *maxSymbolValuePtr) */
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static size_t HIST_count_parallel_wksp(
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unsigned* count, unsigned* maxSymbolValuePtr,
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const void* source, size_t sourceSize,
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HIST_checkInput_e check,
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U32* const workSpace)
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{
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const BYTE* ip = (const BYTE*)source;
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const BYTE* const iend = ip+sourceSize;
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size_t const countSize = (*maxSymbolValuePtr + 1) * sizeof(*count);
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unsigned max=0;
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U32* const Counting1 = workSpace;
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U32* const Counting2 = Counting1 + 256;
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U32* const Counting3 = Counting2 + 256;
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U32* const Counting4 = Counting3 + 256;
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/* safety checks */
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assert(*maxSymbolValuePtr <= 255);
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if (!sourceSize) {
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ZSTD_memset(count, 0, countSize);
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*maxSymbolValuePtr = 0;
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return 0;
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}
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ZSTD_memset(workSpace, 0, 4*256*sizeof(unsigned));
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/* by stripes of 16 bytes */
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{ U32 cached = MEM_read32(ip); ip += 4;
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while (ip < iend-15) {
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U32 c = cached; cached = MEM_read32(ip); ip += 4;
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Counting1[(BYTE) c ]++;
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Counting2[(BYTE)(c>>8) ]++;
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Counting3[(BYTE)(c>>16)]++;
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Counting4[ c>>24 ]++;
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c = cached; cached = MEM_read32(ip); ip += 4;
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Counting1[(BYTE) c ]++;
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Counting2[(BYTE)(c>>8) ]++;
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Counting3[(BYTE)(c>>16)]++;
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Counting4[ c>>24 ]++;
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c = cached; cached = MEM_read32(ip); ip += 4;
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Counting1[(BYTE) c ]++;
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Counting2[(BYTE)(c>>8) ]++;
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Counting3[(BYTE)(c>>16)]++;
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Counting4[ c>>24 ]++;
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c = cached; cached = MEM_read32(ip); ip += 4;
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Counting1[(BYTE) c ]++;
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Counting2[(BYTE)(c>>8) ]++;
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Counting3[(BYTE)(c>>16)]++;
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Counting4[ c>>24 ]++;
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}
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ip-=4;
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}
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/* finish last symbols */
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while (ip<iend) Counting1[*ip++]++;
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{ U32 s;
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for (s=0; s<256; s++) {
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Counting1[s] += Counting2[s] + Counting3[s] + Counting4[s];
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if (Counting1[s] > max) max = Counting1[s];
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} }
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{ unsigned maxSymbolValue = 255;
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while (!Counting1[maxSymbolValue]) maxSymbolValue--;
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if (check && maxSymbolValue > *maxSymbolValuePtr) return ERROR(maxSymbolValue_tooSmall);
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*maxSymbolValuePtr = maxSymbolValue;
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ZSTD_memmove(count, Counting1, countSize); /* in case count & Counting1 are overlapping */
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}
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return (size_t)max;
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}
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/* HIST_countFast_wksp() :
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* Same as HIST_countFast(), but using an externally provided scratch buffer.
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* `workSpace` is a writable buffer which must be 4-bytes aligned,
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* `workSpaceSize` must be >= HIST_WKSP_SIZE
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*/
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size_t HIST_countFast_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
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const void* source, size_t sourceSize,
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void* workSpace, size_t workSpaceSize)
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{
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if (sourceSize < 1500) /* heuristic threshold */
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return HIST_count_simple(count, maxSymbolValuePtr, source, sourceSize);
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if ((size_t)workSpace & 3) return ERROR(GENERIC); /* must be aligned on 4-bytes boundaries */
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if (workSpaceSize < HIST_WKSP_SIZE) return ERROR(workSpace_tooSmall);
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return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, trustInput, (U32*)workSpace);
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}
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/* HIST_count_wksp() :
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* Same as HIST_count(), but using an externally provided scratch buffer.
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* `workSpace` size must be table of >= HIST_WKSP_SIZE_U32 unsigned */
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size_t HIST_count_wksp(unsigned* count, unsigned* maxSymbolValuePtr,
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const void* source, size_t sourceSize,
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void* workSpace, size_t workSpaceSize)
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{
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if ((size_t)workSpace & 3) return ERROR(GENERIC); /* must be aligned on 4-bytes boundaries */
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if (workSpaceSize < HIST_WKSP_SIZE) return ERROR(workSpace_tooSmall);
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if (*maxSymbolValuePtr < 255)
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return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, checkMaxSymbolValue, (U32*)workSpace);
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*maxSymbolValuePtr = 255;
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return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, workSpace, workSpaceSize);
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}
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#ifndef ZSTD_NO_UNUSED_FUNCTIONS
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/* fast variant (unsafe : won't check if src contains values beyond count[] limit) */
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size_t HIST_countFast(unsigned* count, unsigned* maxSymbolValuePtr,
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const void* source, size_t sourceSize)
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{
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unsigned tmpCounters[HIST_WKSP_SIZE_U32];
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return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, tmpCounters, sizeof(tmpCounters));
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}
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size_t HIST_count(unsigned* count, unsigned* maxSymbolValuePtr,
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const void* src, size_t srcSize)
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{
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unsigned tmpCounters[HIST_WKSP_SIZE_U32];
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return HIST_count_wksp(count, maxSymbolValuePtr, src, srcSize, tmpCounters, sizeof(tmpCounters));
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}
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#endif
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