_BitScanReverse, _BitScanReverse64
Microsoft Specific
Search the mask data from most significant bit (MSB) to least significant bit (LSB) for a set bit (1).
unsigned char _BitScanReverse(
unsigned long * Index,
unsigned long Mask
);
unsigned char _BitScanReverse64(
unsigned long * Index,
unsigned __int64 Mask
);
Parameters
[out] Index
Loaded with the bit position of the first set bit (1) found.[in] Mask
The 32-bit or 64-bit value to search.
Return Value
0 if the mask is zero; nonzero otherwise.
Remarks
If a set bit is found, the bit position of the first set bit found is returned in the first parameter. If no set bit is found, 0 is returned; otherwise, 1 is returned.
Requirements
Intrinsic |
Architecture |
|---|---|
_BitScanReverse |
x86, IPF, x64 |
_BitScanReverse64 |
IPF, x64 |
Header file <intrin.h>
Example
// BitScanReverse.cpp
// compile with: /EHsc
#include <iostream>
#include <intrin.h>
using namespace std;
#pragma intrinsic(_BitScanReverse)
int main()
{
unsigned long mask = 0x1000;
unsigned long index;
unsigned char isNonzero;
cout << "Enter a positive integer as the mask: " << flush;
cin >> mask;
isNonzero = _BitScanReverse(&index, mask);
if (isNonzero)
{
cout << "Mask: " << mask << " Index: " << index << endl;
}
else
{
cout << "No set bits found. Mask is zero." << endl;
}
}
Input
12
Sample Output
Enter a positive integer as the mask:
Mask: 12 Index: 3