/***********************************************************************
* *
* This software is part of the ast package *
* Copyright (c) 1985-2011 AT&T Intellectual Property *
* and is licensed under the *
* Eclipse Public License, Version 1.0 *
* by AT&T Intellectual Property *
* *
* A copy of the License is available at *
* http://www.eclipse.org/org/documents/epl-v10.html *
* (with md5 checksum b35adb5213ca9657e911e9befb180842) *
* *
* Information and Software Systems Research *
* AT&T Research *
* Florham Park NJ *
* *
* Glenn Fowler <gsf@research.att.com> *
* David Korn <dgk@research.att.com> *
* Phong Vo <kpv@research.att.com> *
* *
***********************************************************************/
#include "dthdr.h"
/* Hashing a string into an unsigned integer.
** The basic method is to continuingly accumulate bytes and multiply
** with some given prime. The length n of the string is added last.
** The recurrent equation is like this:
** h[k] = (h[k-1] + bytes)*prime for 0 <= k < n
** h[n] = (h[n-1] + n)*prime
** The prime is chosen to have a good distribution of 1-bits so that
** the multiplication will distribute the bits in the accumulator well.
** The below code accumulates 2 bytes at a time for speed.
**
** Written by Kiem-Phong Vo (02/28/03)
*/
#if __STD_C
uint dtstrhash(uint h, Void_t* args, ssize_t n)
#else
uint dtstrhash(h,args,n)
reg uint h;
Void_t* args;
ssize_t n;
#endif
{
unsigned char *s = (unsigned char*)args;
if(n <= 0)
{ for(; *s != 0; s += s[1] ? 2 : 1)
h = (h + (s[0]<<8) + s[1])*DT_PRIME;
n = s - (unsigned char*)args;
}
else
{ unsigned char* ends;
for(ends = s+n-1; s < ends; s += 2)
h = (h + (s[0]<<8) + s[1])*DT_PRIME;
if(s <= ends)
h = (h + (s[0]<<8))*DT_PRIME;
}
return (h+n)*DT_PRIME;
}