pg_lfind.h

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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 */