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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