ref: 49bd8a86f3a07c4f54df94838c07fa653d725afa
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) { ulong bh, bl, ah, al; bl = b; bh = b >> 32; al = a; ah = a >> 32; *r = (((uvlong)al*(uvlong)bl)>>32) + ((uvlong)al*(uvlong)bh) + ((uvlong)ah*(uvlong)bl) + (((uvlong)ah*(uvlong)bh)<<32); }