_BitScanReverse, _BitScanReverse64
Microsoft Specific
Search the mask data from most significant bit (MSB) to least significant bit (LSB) for a set bit (1).
Syntax
unsigned char _BitScanReverse(
unsigned long * Index,
unsigned long Mask
);
unsigned char _BitScanReverse64(
unsigned long * Index,
unsigned __int64 Mask
);
Parameters
Index
[out] Loaded with the bit position of the first set bit (1) found. Otherwise, undefined.
Mask
[in] The 32-bit or 64-bit value to search.
Return value
Nonzero if any bit was set in Mask, or 0 if no set bits were found.
Requirements
| Intrinsic | Architecture | Header |
|---|---|---|
_BitScanReverse |
x86, ARM, x64, ARM64 | <intrin.h> |
_BitScanReverse64 |
ARM64, x64 | <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;
}
}
12
Enter a positive integer as the mask:
Mask: 12 Index: 3
END Microsoft Specific