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/* Copyright (c) 1997-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <nss.h>
/* This is from libc/db/hash/hash_func.c, hash3 is static there */
/*
* This is INCREDIBLY ugly, but fast. We break the string up into 4 byte
* units. On the first time through the loop we get the "leftover bytes"
* (len % 4). On every other iteration, we perform a 4x unrolled version
* HASHC. Further unrolling does not appear to help.
*
* OZ's original sdbm hash
*/
uint32_t
__nss_hash (const void *keyarg, size_t len)
{
enum
{
HASH_CONST_P0 = 1, /* (uint32_t)(65599 ^ 0). */
HASH_CONST_P1 = 65599, /* (uint32_t)(65599 ^ 1). */
HASH_CONST_P2 = 8261505, /* (uint32_t)(65599 ^ 2). */
HASH_CONST_P3 = 780587199, /* (uint32_t)(65599 ^ 3). */
HASH_CONST_P4 = 1139564289 /* (uint32_t)(65599 ^ 4). */
};
const unsigned char *key;
uint32_t h;
#define HASHC h = *key++ + HASH_CONST_P1 * h
h = 0;
key = keyarg;
if (len > 0)
{
switch ((len & (4 - 1)))
{
case 0:
/* h starts out as zero so no need to include the multiply. */
h = *key++;
/* FALLTHROUGH */
case 3:
HASHC;
/* FALLTHROUGH */
case 2:
HASHC;
/* FALLTHROUGH */
case 1:
HASHC;
/* FALLTHROUGH */
}
uint32_t c0, c1, c2, c3;
for (--len; len >= 4; len -= 4)
{
c0 = (unsigned char) *(key + 0);
c1 = (unsigned char) *(key + 1);
c2 = (unsigned char) *(key + 2);
c3 = (unsigned char) *(key + 3);
h = HASH_CONST_P4 * h + HASH_CONST_P3 * c0 + HASH_CONST_P2 * c1
+ HASH_CONST_P1 * c2 + HASH_CONST_P0 * c3;
key += 4;
}
}
return h;
}
libc_hidden_def (__nss_hash)
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