3d155d4b6c
The prior unrolling didn't really do much as it left the dependency chain between iterations. Unrolled the loop for 4 so 4x multiplies could be pipelined in out-of-order machines. Results for __nss_hash Benchmarked on Tigerlake: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz Time as Geometric Mean of N=25 runs Geometric of all benchmark New / Old: 0.845 type, length, New Time, Old Time, New Time / Old Time fixed, 0, 4.019, 3.729, 1.078 fixed, 1, 4.95, 5.707, 0.867 fixed, 2, 5.152, 5.657, 0.911 fixed, 3, 4.641, 5.721, 0.811 fixed, 4, 5.551, 5.81, 0.955 fixed, 5, 6.525, 6.552, 0.996 fixed, 6, 6.711, 6.561, 1.023 fixed, 7, 6.715, 6.767, 0.992 fixed, 8, 7.874, 7.915, 0.995 fixed, 9, 8.888, 9.767, 0.91 fixed, 10, 8.959, 9.762, 0.918 fixed, 11, 9.188, 9.987, 0.92 fixed, 12, 9.708, 10.618, 0.914 fixed, 13, 10.393, 11.14, 0.933 fixed, 14, 10.628, 12.097, 0.879 fixed, 15, 10.982, 12.965, 0.847 fixed, 16, 11.851, 14.429, 0.821 fixed, 32, 24.334, 34.414, 0.707 fixed, 64, 55.618, 86.688, 0.642 fixed, 128, 118.261, 224.36, 0.527 fixed, 256, 256.183, 538.629, 0.476 random, 2, 11.194, 11.556, 0.969 random, 4, 17.516, 17.205, 1.018 random, 8, 23.501, 20.985, 1.12 random, 16, 28.131, 29.212, 0.963 random, 32, 35.436, 38.662, 0.917 random, 64, 45.74, 58.868, 0.777 random, 128, 75.394, 121.963, 0.618 random, 256, 139.524, 260.726, 0.535 Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
85 lines
2.3 KiB
C
85 lines
2.3 KiB
C
/* Copyright (c) 1997-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <nss.h>
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/* This is from libc/db/hash/hash_func.c, hash3 is static there */
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/*
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* This is INCREDIBLY ugly, but fast. We break the string up into 4 byte
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* units. On the first time through the loop we get the "leftover bytes"
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* (len % 4). On every other iteration, we perform a 4x unrolled version
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* HASHC. Further unrolling does not appear to help.
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*
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* OZ's original sdbm hash
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*/
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uint32_t
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__nss_hash (const void *keyarg, size_t len)
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{
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enum
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{
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HASH_CONST_P0 = 1, /* (uint32_t)(65599 ^ 0). */
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HASH_CONST_P1 = 65599, /* (uint32_t)(65599 ^ 1). */
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HASH_CONST_P2 = 8261505, /* (uint32_t)(65599 ^ 2). */
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HASH_CONST_P3 = 780587199, /* (uint32_t)(65599 ^ 3). */
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HASH_CONST_P4 = 1139564289 /* (uint32_t)(65599 ^ 4). */
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};
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const unsigned char *key;
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uint32_t h;
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#define HASHC h = *key++ + HASH_CONST_P1 * h
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h = 0;
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key = keyarg;
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if (len > 0)
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{
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switch ((len & (4 - 1)))
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{
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case 0:
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/* h starts out as zero so no need to include the multiply. */
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h = *key++;
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/* FALLTHROUGH */
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case 3:
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HASHC;
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/* FALLTHROUGH */
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case 2:
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HASHC;
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/* FALLTHROUGH */
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case 1:
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HASHC;
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/* FALLTHROUGH */
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}
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uint32_t c0, c1, c2, c3;
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for (--len; len >= 4; len -= 4)
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{
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c0 = (unsigned char) *(key + 0);
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c1 = (unsigned char) *(key + 1);
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c2 = (unsigned char) *(key + 2);
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c3 = (unsigned char) *(key + 3);
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h = HASH_CONST_P4 * h + HASH_CONST_P3 * c0 + HASH_CONST_P2 * c1
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+ HASH_CONST_P1 * c2 + HASH_CONST_P0 * c3;
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key += 4;
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}
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}
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return h;
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}
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libc_hidden_def (__nss_hash)
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