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#include "safemult.h"
/* return 1 for overflow, 0 for ok */
int umult64(uint64 a,uint64 b,uint64* c) {
uint32 ahi=a>>32;
uint32 alo=(a&0xffffffff);
uint32 bhi=b>>32;
uint32 blo=(b&0xffffffff);
// a=ahi*x+alo, b=bhi*x+blo
// a*b = (ahi*x+alo) * (bhi*x+blo)
// = ahi*x*bhi*x + ahi*x*blo + alo*bhi*x + alo*blo
// -> overflow if ahi*bhi != zero */
if (ahi && bhi) return 0;
a=(uint64)(ahi)*blo+(uint64)(alo)*bhi;
if (a>0xffffffff) return 0;
*c=(a<<32)+(uint64)(alo)*blo;
return 1;
}