Subversion Repositories planix.SVN

#include <u.h>

/* mul64fract(uvlong*r, uvlong a, uvlong b)

 *

 * Multiply two 64 numbers and return the middle 64 bits of the 128 bit result.

 *

 * The assumption is that one of the numbers is a 

 * fixed point number with the integer portion in the

 * high word and the fraction in the low word.

 *

 * There should be an assembler version of this routine

 * for each architecture.  This one is intended to

 * make ports easier.

 *

 *	ignored		r0 = lo(a0*b0)

 *	lsw of result	r1 = hi(a0*b0) +lo(a0*b1) +lo(a1*b0)

 *	msw of result	r2 = 		hi(a0*b1) +hi(a1*b0) +lo(a1*b1)

 *	ignored		r3 = hi(a1*b1)

 */

void

mul64fract(uvlong *r, uvlong a, uvlong b)

{

	uvlong bh, bl;

	uvlong ah, al;

	uvlong res;

	bl = b & 0xffffffffULL;

	bh = b >> 32;

	al = a & 0xffffffffULL;

	ah = a >> 32;

	res = (al*bl)>>32;

	res += (al*bh);

	res += (ah*bl);

	res += (ah*bh)<<32;

	*r = res;

}