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//------------------------------------------------------------------------------
// GB_iso_reduce_worker: reduce n entries, all equal to a, to the scalar s
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
// Some built-in monoids could be done in O(1) time, but this takes at most
// O(log (n)) time which is fast enough, even if n = 2^60, and it works for all
// monoids including user-defined ones.
#include "GB_reduce.h"
void GB_iso_reduce_worker
(
GB_void *restrict s, // output scalar
GxB_binary_function freduce, // reduction function
GB_void *restrict a, // iso value of A
uint64_t n, // number of entries in A to reduce
size_t zsize // size of s and a
)
{
if (n <= 1)
{
memcpy (s, a, zsize) ;
}
else
{
// reduce floor (n/2) entries to the scalar s
GB_iso_reduce_worker (s, freduce, a, n/2, zsize) ;
// s = freduce (s, s)
freduce (s, s, s) ;
// if n is even, s is now the reduction of 2*floor(n/2) == n entries.
// if n is odd, s is now the reduction of 2*floor(n/2) == n-1 entries.
if (n & 1)
{
// n is odd, so add more more entry with s = freduce (s, a)
freduce (s, s, a) ;
}
}
}
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