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//------------------------------------------------------------------------------
// GB_cumsum: cumlative sum of an array
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
// Compute the cumulative sum of an array count[0:n], of size n+1:
// k = sum (count [0:n-1] != 0) ;
// count = cumsum ([0 count[0:n-1]]) ;
// That is, count [j] on input is overwritten with sum (count [0..j-1]).
// On input, count [n] is not accessed and is implicitly zero on input.
// On output, count [n] is the total sum.
#include "GB.h"
GB_PUBLIC
void GB_cumsum // cumulative sum of an array
(
int64_t *restrict count, // size n+1, input/output
const int64_t n,
int64_t *restrict kresult, // return k, if needed by the caller
int nthreads,
GB_Context Context
)
{
//--------------------------------------------------------------------------
// check inputs
//--------------------------------------------------------------------------
ASSERT (count != NULL) ;
ASSERT (n >= 0) ;
//--------------------------------------------------------------------------
// determine # of threads to use
//--------------------------------------------------------------------------
#if !defined ( _OPENMP )
nthreads = 1 ;
#endif
if (nthreads > 1)
{
nthreads = GB_IMIN (nthreads, n / (64 * 1024)) ;
nthreads = GB_IMAX (nthreads, 1) ;
}
//--------------------------------------------------------------------------
// count = cumsum ([0 count[0:n-1]]) ;
//--------------------------------------------------------------------------
if (kresult == NULL)
{
if (nthreads <= 2)
{
//------------------------------------------------------------------
// cumsum with one thread
//------------------------------------------------------------------
int64_t s = 0 ;
for (int64_t i = 0 ; i < n ; i++)
{
int64_t c = count [i] ;
count [i] = s ;
s += c ;
}
count [n] = s ;
}
else
{
//------------------------------------------------------------------
// cumsum with multiple threads
//------------------------------------------------------------------
// allocate workspace
GB_WERK_DECLARE (ws, int64_t) ;
GB_WERK_PUSH (ws, nthreads, int64_t) ;
if (ws == NULL)
{
// out of memory; use a single thread instead
GB_cumsum (count, n, NULL, 1, NULL) ;
return ;
}
int tid ;
#pragma omp parallel for num_threads(nthreads) schedule(static)
for (tid = 0 ; tid < nthreads ; tid++)
{
// each task sums up its own part
int64_t istart, iend ;
GB_PARTITION (istart, iend, n, tid, nthreads) ;
int64_t s = 0 ;
for (int64_t i = istart ; i < iend ; i++)
{
s += count [i] ;
}
ws [tid] = s ;
}
#pragma omp parallel for num_threads(nthreads) schedule(static)
for (tid = 0 ; tid < nthreads ; tid++)
{
// each tasks computes the cumsum of its own part
int64_t istart, iend ;
GB_PARTITION (istart, iend, n, tid, nthreads) ;
int64_t s = 0 ;
for (int i = 0 ; i < tid ; i++)
{
s += ws [i] ;
}
for (int64_t i = istart ; i < iend ; i++)
{
int64_t c = count [i] ;
count [i] = s ;
s += c ;
}
if (iend == n)
{
count [n] = s ;
}
}
// free workspace
GB_WERK_POP (ws, int64_t) ;
}
}
else
{
if (nthreads <= 2)
{
//------------------------------------------------------------------
// cumsum with one thread, also compute k
//------------------------------------------------------------------
int64_t k = 0 ;
int64_t s = 0 ;
for (int64_t i = 0 ; i < n ; i++)
{
int64_t c = count [i] ;
if (c != 0) k++ ;
count [i] = s ;
s += c ;
}
count [n] = s ;
(*kresult) = k ;
}
else
{
//------------------------------------------------------------------
// cumsum with multiple threads, also compute k
//------------------------------------------------------------------
// allocate workspace
GB_WERK_DECLARE (ws, int64_t) ;
GB_WERK_DECLARE (wk, int64_t) ;
GB_WERK_PUSH (ws, nthreads, int64_t) ;
GB_WERK_PUSH (wk, nthreads, int64_t) ;
if (ws == NULL || wk == NULL)
{
// out of memory; use a single thread instead
GB_WERK_POP (wk, int64_t) ;
GB_WERK_POP (ws, int64_t) ;
GB_cumsum (count, n, kresult, 1, NULL) ;
return ;
}
int tid ;
#pragma omp parallel for num_threads(nthreads) schedule(static)
for (tid = 0 ; tid < nthreads ; tid++)
{
// each task sums up its own part
int64_t istart, iend ;
GB_PARTITION (istart, iend, n, tid, nthreads) ;
int64_t k = 0 ;
int64_t s = 0 ;
for (int64_t i = istart ; i < iend ; i++)
{
int64_t c = count [i] ;
if (c != 0) k++ ;
s += c ;
}
ws [tid] = s ;
wk [tid] = k ;
}
#pragma omp parallel for num_threads(nthreads) schedule(static)
for (tid = 0 ; tid < nthreads ; tid++)
{
// each task computes the cumsum of its own part
int64_t istart, iend ;
GB_PARTITION (istart, iend, n, tid, nthreads) ;
int64_t s = 0 ;
for (int i = 0 ; i < tid ; i++)
{
s += ws [i] ;
}
for (int64_t i = istart ; i < iend ; i++)
{
int64_t c = count [i] ;
count [i] = s ;
s += c ;
}
if (iend == n)
{
count [n] = s ;
}
}
int64_t k = 0 ;
for (int tid = 0 ; tid < nthreads ; tid++)
{
k += wk [tid] ;
}
(*kresult) = k ;
// free workspace
GB_WERK_POP (wk, int64_t) ;
GB_WERK_POP (ws, int64_t) ;
}
}
}
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