ref: 66719fb3ea15351f8860cc6696993357a60ab238
dir: /sys/src/9/port/mul64fract.c/
#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; }