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_BitScanReverse, _BitScanReverse64 | Microsoft Docs
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_BitScanReverse64
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_BitScanReverse
_BitScanReverse64_cpp
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bsr instruction
_BitScanReverse intrinsic
BitScanReverse intrinsic
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_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
);
[out] Index
[in] Mask
Nonzero if Index was set, or 0 if no set bits were found.
Intrinsic
Architecture
Header
_BitScanReversex86, ARM, [!INCLUDEvcprx64 ]
<intrin.h>
_BitScanReverse64ARM, [!INCLUDEvcprx64 ]
// 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;
}
}
Enter a positive integer as the mask:
Mask: 12 Index: 3
END Microsoft Specific
Compiler Intrinsics