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Microsoft Specific

Returns the high 64 bits of the product of two 64-bit signed integers.

__int64 __mulh( 
   __int64 a, 
   __int64 b 

[in] a

The first number to multiply.

[in] b

The second number to multiply.

The high 64 bits of the 128-bit result of the multiplication.





Header file <intrin.h>

This routine is only available as an intrinsic.

// mulh.cpp
// processor: x64
#include <stdio.h>
#include <intrin.h>

#pragma intrinsic (__mulh)

int main()
    __int64 a = 0x0fffffffffffffffI64;
    __int64 b = 0xf0000000I64;

    __int64 result = __mulh(a, b); // the high 64 bits
    __int64 result2 = a * b; // the low 64 bits

    printf_s(" %#I64x * %#I64x = %#I64x%I64x\n",
             a, b, result, result2);
 0xfffffffffffffff * 0xf0000000 = 0xeffffffffffffff10000000