Microsoft Specific

Multiplies two 64-bit integers passed in as the first two arguments and puts the high 64 bits of the product in the 64-bit integer pointed to by HighProduct and returns the low 64 bits of the product.

__int64 _mul128(
   __int64 Multiplier,
   __int64 Multiplicand,
   __int64 *HighProduct
);

Multiplier
[in] The first 64-bit integer to multiply.

Multiplicand
[in] The second 64-bit integer to multiply.

HighProduct
[out] The high 64 bits of the product.

The low 64 bits of the product.

Header file <intrin.h>

// mul128.c
// processor: x64
#include <stdio.h>
#include <intrin.h>

#pragma intrinsic(_mul128)

int main()
{
    __int64 a = 0x0fffffffffffffffI64;
    __int64 b = 0xf0000000I64;
    __int64 c, d;

    d = _mul128(a, b, &c);

    printf_s("%#I64x * %#I64x = %#I64x%I64x\n", a, b, c, d);
}

0xfffffffffffffff * 0xf0000000 = 0xeffffffffffffff10000000

END Microsoft Specific

Compiler intrinsics