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Microsoft Specific

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

unsigned __int64 _umul128( 
   unsigned __int64 Multiplier, 
   unsigned __int64 Multiplicand, 
   unsigned __int64 *HighProduct 

[in] Multiplier

The first 64-bit integer to multiply.

[in] Multiplicand

The second 64-bit integer to multiply.

[out] HighProduct

The high 64 bits of the product.

The low 64 bits of the product.




IPF, x64

Header file <intrin.h>

// umul128.c
// processor: IPF, x64

#include <stdio.h>
#include <intrin.h>

#pragma intrinsic(_umul128)

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

    d = _umul128(a, b, &c);

    printf_s("%#I64x * %#I64x = %#I64x%I64x\n", a, b, c, d);
0xfffffffffffffff * 0xf0000000 = 0xeffffffffffffff10000000