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/*-------------------------------------------------------------------------
*
* pg_lfind.h
* Optimized linear search routines using SIMD intrinsics where
* available.
*
* Copyright (c) 2022-2025, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/include/port/pg_lfind.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_LFIND_H
#define PG_LFIND_H
#include "port/simd.h"
/*
* pg_lfind8
*
* Return true if there is an element in 'base' that equals 'key', otherwise
* return false.
*/
static inline bool
pg_lfind8(uint8 key, uint8 *base, uint32 nelem)
{
uint32 i;
/* round down to multiple of vector length */
uint32 tail_idx = nelem & ~(sizeof(Vector8) - 1);
Vector8 chunk;
for (i = 0; i < tail_idx; i += sizeof(Vector8))
{
vector8_load(&chunk, &base[i]);
if (vector8_has(chunk, key))
return true;
}
/* Process the remaining elements one at a time. */
for (; i < nelem; i++)
{
if (key == base[i])
return true;
}
return false;
}
/*
* pg_lfind8_le
*
* Return true if there is an element in 'base' that is less than or equal to
* 'key', otherwise return false.
*/
static inline bool
pg_lfind8_le(uint8 key, uint8 *base, uint32 nelem)
{
uint32 i;
/* round down to multiple of vector length */
uint32 tail_idx = nelem & ~(sizeof(Vector8) - 1);
Vector8 chunk;
for (i = 0; i < tail_idx; i += sizeof(Vector8))
{
vector8_load(&chunk, &base[i]);
if (vector8_has_le(chunk, key))
return true;
}
/* Process the remaining elements one at a time. */
for (; i < nelem; i++)
{
if (base[i] <= key)
return true;
}
return false;
}
/*
* pg_lfind32_one_by_one_helper
*
* Searches the array of integers one-by-one. The caller is responsible for
* ensuring that there are at least "nelem" integers in the array.
*/
static inline bool
pg_lfind32_one_by_one_helper(uint32 key, const uint32 *base, uint32 nelem)
{
for (uint32 i = 0; i < nelem; i++)
{
if (key == base[i])
return true;
}
return false;
}
#ifndef USE_NO_SIMD
/*
* pg_lfind32_simd_helper
*
* Searches one 4-register-block of integers. The caller is responsible for
* ensuring that there are at least 4-registers-worth of integers remaining.
*/
static inline bool
pg_lfind32_simd_helper(const Vector32 keys, const uint32 *base)
{
const uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
Vector32 vals1,
vals2,
vals3,
vals4,
result1,
result2,
result3,
result4,
tmp1,
tmp2,
result;
/* load the next block into 4 registers */
vector32_load(&vals1, base);
vector32_load(&vals2, &base[nelem_per_vector]);
vector32_load(&vals3, &base[nelem_per_vector * 2]);
vector32_load(&vals4, &base[nelem_per_vector * 3]);
/* compare each value to the key */
result1 = vector32_eq(keys, vals1);
result2 = vector32_eq(keys, vals2);
result3 = vector32_eq(keys, vals3);
result4 = vector32_eq(keys, vals4);
/* combine the results into a single variable */
tmp1 = vector32_or(result1, result2);
tmp2 = vector32_or(result3, result4);
result = vector32_or(tmp1, tmp2);
/* return whether there was a match */
return vector32_is_highbit_set(result);
}
#endif /* ! USE_NO_SIMD */
/*
* pg_lfind32
*
* Return true if there is an element in 'base' that equals 'key', otherwise
* return false.
*/
static inline bool
pg_lfind32(uint32 key, const uint32 *base, uint32 nelem)
{
#ifndef USE_NO_SIMD
uint32 i = 0;
/*
* For better instruction-level parallelism, each loop iteration operates
* on a block of four registers.
*/
const Vector32 keys = vector32_broadcast(key); /* load copies of key */
const uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
const uint32 nelem_per_iteration = 4 * nelem_per_vector;
/* round down to multiple of elements per iteration */
const uint32 tail_idx = nelem & ~(nelem_per_iteration - 1);
#if defined(USE_ASSERT_CHECKING)
bool assert_result = pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
/*
* If there aren't enough elements for the SIMD code, use the standard
* one-by-one linear search code.
*/
if (nelem < nelem_per_iteration)
return pg_lfind32_one_by_one_helper(key, base, nelem);
/*
* Process as many elements as possible with a block of 4 registers.
*/
do
{
if (pg_lfind32_simd_helper(keys, &base[i]))
{
Assert(assert_result == true);
return true;
}
i += nelem_per_iteration;
} while (i < tail_idx);
/*
* Process the last 'nelem_per_iteration' elements in the array with a
* 4-register block. This will cause us to check a subset of the elements
* more than once, but that won't affect correctness, and testing has
* demonstrated that this helps more cases than it harms.
*/
Assert(assert_result == pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]));
return pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]);
#else
/* Process the elements one at a time. */
return pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
}
#endif /* PG_LFIND_H */
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