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//------------------------------------------------------------------------------
// GB_hyper_hash_lookup: find k so that j == Ah [k], using the A->Y hyper_hash
//------------------------------------------------------------------------------
// SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//------------------------------------------------------------------------------
#ifndef GB_HYPER_HASH_LOOKUP_H
#define GB_HYPER_HASH_LOOKUP_H
// Let j = Ah [k]
// k = A->Y (j, hash(j)), if present, or k=-1 if not found.
static
#ifdef GB_CUDA_KERNEL
__device__ __inline__
#else
inline
#endif
int64_t GB_hyper_hash_lookup // k if j==Ah[k], or -1 if not found
(
// input, not modified
const int64_t *restrict Ap, // A->p [0..A->nvec]: pointers to vectors
const int64_t *restrict Yp, // A->Y->p
const int64_t *restrict Yi, // A->Y->i
const int64_t *restrict Yx, // A->Y->x
const int64_t hash_bits, // A->Y->vdim-1, which is hash table size-1
const int64_t j, // find j in Ah [0..anvec-1], using A->Y
int64_t *restrict pstart, // start of vector: Ap [k]
int64_t *restrict pend // end of vector: Ap [k+1]
)
{
//--------------------------------------------------------------------------
// determine the hash bucket that would contain vector j
//--------------------------------------------------------------------------
const int64_t jhash = GB_HASHF2 (j, hash_bits) ;
//--------------------------------------------------------------------------
// search for j in the jhash bucket: Yi [Yp [jhash] ... Yp [jhash+1]-1]
//--------------------------------------------------------------------------
const int64_t ypstart = Yp [jhash] ;
const int64_t ypend = Yp [jhash+1] ;
int64_t k = -1 ;
if ((ypend - ypstart) > 256)
{
// The hash bucket jhash has over 256 entries, which is a very hign
// number of collisions. The load factor of the hash table ranges from
// 2 to 4. Do a binary search as a fallback.
bool found ;
int64_t p = ypstart ;
int64_t pright = ypend - 1 ;
GB_BINARY_SEARCH (j, Yi, p, pright, found) ;
if (found)
{
k = Yx [p] ;
}
}
else
{
// Linear-time search for j in the jhash bucket.
for (int64_t p = ypstart ; p < ypend ; p++)
{
if (j == Yi [p])
{
// found: j = Ah [k] where k is given by k = Yx [p]
k = Yx [p] ;
break ;
}
}
}
//--------------------------------------------------------------------------
// if found, return the start and end of A(:,j)
//--------------------------------------------------------------------------
if (k >= 0)
{
// found: j == Ah [k], get the vector A(:,j)
(*pstart) = Ap [k] ;
(*pend ) = Ap [k+1] ;
}
else
{
// not found: j is not in the hyperlist Ah [0..anvec-1]
(*pstart) = -1 ;
(*pend ) = -1 ;
}
return (k) ;
}
#endif
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