We recommend using Visual Studio 2017



The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at __mulh.

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  

Compiler Intrinsics