_bittestandreset, _bittestandreset64


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Microsoft Specific**

Generate the instruction which examines bit b of the address a, returns its current value, and resets the bit to 0.


unsigned char _bittestandreset(  
   long *a,  
   long b  
unsigned char _bittestandreset64(  
   __int64 *a,  
   __int64 b  


[in, out] a
A pointer to the memory to examine.

[in] b
The bit position to test.

Return Value

The bit at the position specified.


Intrinsic Architecture
_bittestandreset x86, ARM, x64
_bittestandreset64 x64

Header file <intrin.h>


This routine is only available as an intrinsic.


// bittestandreset.cpp  
// processor: x86, IPF, x64  
#include <stdio.h>  
#include <limits.h>  
#include <intrin.h>  
#pragma intrinsic(_bittestandreset)  
// Check the sign bit and reset to 0 (taking the absolute value)  
// Returns 0 if the number is positive or zero  
// Returns 1 if the number is negative  
unsigned char absolute_value(long* p)  
   const int SIGN_BIT = 31;  
   return _bittestandreset(p, SIGN_BIT);  
int main()  
    long i = -112;  
    unsigned char result;  
    // Check the sign bit and reset to 0 (taking the absolute value)  
    result = absolute_value(&i);  
    if (result == 1)  
        printf_s("The number was negative.\n");     
The number was negative.  

END Microsoft Specific

See Also

Compiler Intrinsics