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#if defined(__GNUC__) && (__GNUC__ >= 5)
#include "uint64.h"
int umult64(uint64 a,uint64 b,uint64* c) { return !__builtin_mul_overflow(a,b,c); }
#else
#include "haveuint128.h"
#include "safemult.h"
#if defined(HAVE_UINT128)
int umult64(uint64 a,uint64 b,uint64* c) {
__uint128_t x=((__uint128_t)a)*b;
if ((*c=(uint64)x) != x) return 0;
return 1;
}
#else
/* 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;
{
uint64 x=(uint64)(alo)*blo;
if (x+(a<<32) < x) return 0;
*c=x+(a<<32);
}
return 1;
}
#endif
#endif
#ifdef UNITTEST
#include <assert.h>
int main() {
uint64 a;
assert(umult64(4,0x8000000000000000ull,&a)==0);
assert(umult64(16,0x4500000000000000ull,&a)==0); // make sure we don't fall for "if a*b<a && a*b<b"
assert(umult64(5,10,&a)==1 && a==50);
assert(umult64(0x60000000,0x10000000,&a)==1 && a==0x600000000000000);
return 0;
}
#endif