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//------------------------------------------------------------------------------
// GB_Iterator_rc_seek: seek a row/col iterator to A(:,j) or to jth vector of A
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2025, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
// Seek a row iterator to A(j,:), a col iterator to A(:,j). If jth_vector is
// true, seek to the jth vector instead. For sparse, bitmap, or full matrices,
// this is the same as A(j,:) for a row iterator or A(:,j) for a col iterator.
// The jth_vector parameter only affects how hypersparse matrices are
// traversed.
#include "GB.h"
GrB_Info GB_Iterator_rc_seek
(
GxB_Iterator iterator,
uint64_t j_input,
bool jth_vector
)
{
//--------------------------------------------------------------------------
// check if the iterator is exhausted
//--------------------------------------------------------------------------
int64_t j = (int64_t) j_input ;
if (j >= ((jth_vector) ? iterator->anvec : iterator->avdim))
{
iterator->pstart = 0 ;
iterator->pend = 0 ;
iterator->p = 0 ;
iterator->k = iterator->anvec ;
return (GxB_EXHAUSTED) ;
}
//--------------------------------------------------------------------------
// attach the iterator to A(:,j)
//--------------------------------------------------------------------------
switch (iterator->A_sparsity)
{
default:
case GxB_SPARSE :
{
// attach to A(:,j), which is also the jth vector of A
iterator->pstart = GB_IGET (iterator->Ap, j) ;
iterator->pend = GB_IGET (iterator->Ap, j+1) ;
iterator->p = iterator->pstart ;
iterator->k = j ;
}
break ;
case GxB_HYPERSPARSE :
{
int64_t k ;
if (jth_vector)
{
// attach to the jth vector of A; this is much faster than
// searching Ah for the value j, to attach to A(:,j)
k = j ;
iterator->pstart = GB_IGET (iterator->Ap, k) ;
iterator->pend = GB_IGET (iterator->Ap, k+1) ;
iterator->p = iterator->pstart ;
iterator->k = k ;
}
else
{
// find k so that j = Ah [k], or if not found, return k as the
// smallest value so that j < Ah [k].
k = 0 ;
if (j > 0)
{
int64_t pright = iterator->anvec-1 ;
if (iterator->Ah32 != NULL)
{
GB_split_binary_search_32 (j, iterator->Ah32,
&k, &pright) ;
}
else
{
GB_split_binary_search_64 (j, iterator->Ah64,
&k, &pright) ;
}
}
}
// If j is found, A(:,j) is the kth vector in the Ah hyperlist.
// If j is not found, the iterator is placed at the first vector
// after j in the hyperlist, if this vector exists.
if (k >= iterator->anvec)
{
// the kth vector does not exist
iterator->pstart = 0 ;
iterator->pend = 0 ;
iterator->p = 0 ;
iterator->k = iterator->anvec ;
return (GxB_EXHAUSTED) ;
}
else
{
// the kth vector exists
iterator->pstart = GB_IGET (iterator->Ap, k) ;
iterator->pend = GB_IGET (iterator->Ap, k+1) ;
iterator->p = iterator->pstart ;
iterator->k = k ;
}
}
break ;
case GxB_BITMAP :
{
// attach to A(:,j), which is also the jth vector of A
iterator->pstart = j * iterator->avlen ;
iterator->pend = (j+1) * iterator->avlen ;
iterator->p = iterator->pstart ;
iterator->k = j ;
return (GB_Iterator_rc_bitmap_next (iterator)) ;
}
break ;
case GxB_FULL :
{
// attach to A(:,j), which is also the jth vector of A
iterator->pstart = j * iterator->avlen ;
iterator->pend = (j+1) * iterator->avlen ;
iterator->p = iterator->pstart ;
iterator->k = j ;
}
break ;
}
return ((iterator->p >= iterator->pend) ? GrB_NO_VALUE : GrB_SUCCESS) ;
}
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