#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)
*/

uint dtstrhash(reg uint h, void* args, reg int n)
{
	reg 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
	{	reg 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;
}
