1/***********************************************************************
2*                                                                      *
3*               This software is part of the ast package               *
4*          Copyright (c) 1985-2011 AT&T Intellectual Property          *
5*                      and is licensed under the                       *
6*                  Common Public License, Version 1.0                  *
7*                    by AT&T Intellectual Property                     *
8*                                                                      *
9*                A copy of the License is available at                 *
10*            http://www.opensource.org/licenses/cpl1.0.txt             *
11*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
12*                                                                      *
13*              Information and Software Systems Research               *
14*                            AT&T Research                             *
15*                           Florham Park NJ                            *
16*                                                                      *
17*                 Glenn Fowler <gsf@research.att.com>                  *
18*                  David Korn <dgk@research.att.com>                   *
19*                   Phong Vo <kpv@research.att.com>                    *
20*                                                                      *
21***********************************************************************/
22#include	"dthdr.h"
23
24/* Hashing a string into an unsigned integer.
25** The basic method is to continuingly accumulate bytes and multiply
26** with some given prime. The length n of the string is added last.
27** The recurrent equation is like this:
28**	h[k] = (h[k-1] + bytes)*prime	for 0 <= k < n
29**	h[n] = (h[n-1] + n)*prime
30** The prime is chosen to have a good distribution of 1-bits so that
31** the multiplication will distribute the bits in the accumulator well.
32** The below code accumulates 2 bytes at a time for speed.
33**
34** Written by Kiem-Phong Vo (02/28/03)
35*/
36
37#if __STD_C
38uint dtstrhash(reg uint h, Void_t* args, reg int n)
39#else
40uint dtstrhash(h,args,n)
41reg uint	h;
42Void_t*		args;
43reg int		n;
44#endif
45{
46	reg unsigned char*	s = (unsigned char*)args;
47
48	if(n <= 0)
49	{	for(; *s != 0; s += s[1] ? 2 : 1)
50			h = (h + (s[0]<<8) + s[1])*DT_PRIME;
51		n = s - (unsigned char*)args;
52	}
53	else
54	{	reg unsigned char*	ends;
55		for(ends = s+n-1; s < ends; s += 2)
56			h = (h + (s[0]<<8) + s[1])*DT_PRIME;
57		if(s <= ends)
58			h = (h + (s[0]<<8))*DT_PRIME;
59	}
60	return (h+n)*DT_PRIME;
61}
62