_bittestandset, _bittestandset64
Microsoft Specific
Generate the bts instruction, which examines bit b of the address a, returns its current value, and sets the bit to 1.
unsigned char _bittestandset(
long *a,
long b
);
unsigned char _bittestandset64(
__int64 *a,
__int64 b
);
Parameters
- [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.
Requirements
| Intrinsic | Architecture |
|---|---|
_bittestandset |
x86, IPF, x64 |
_bittestandset64 |
IPF, x64 |
Header file <intrin.h>
Remarks
On the IPF architecture, the bts instruction is not available, so this intrinsic is a custom function that imitates the behavior of bts. This custom function might be slower than a hand-written inline function because it includes overhead, such as handling the case where b is negative, that might be unnecessary in specific cases.
This routine is only available as an intrinsic.
Example
// bittestandset.cpp
// processor: x86, IPF, x64
// This example uses several of the _bittest family of intrinsics
// to implement a Flags class that allows bit level access to an
// integer field.
#include <stdio.h>
#include <intrin.h>
#pragma intrinsic(_bittestandset, _bittestandreset,\
_bittestandcomplement, _bittest)
class Flags
{
private:
long flags;
long* oldValues;
public:
Flags() : flags(0)
{
oldValues = new long[32];
}
~Flags()
{
delete oldValues;
}
void SetFlagBit(long nBit)
{
// We omit range checks on the argument
oldValues[nBit] = _bittestandset(&flags, nBit);
printf_s("Flags: 0x%x\n", flags);
}
void ClearFlagBit(long nBit)
{
oldValues[nBit] = _bittestandreset(&flags, nBit);
printf_s("Flags: 0x%x\n", flags);
}
unsigned char GetFlagBit(long nBit)
{
unsigned char result = _bittest(&flags, nBit);
printf_s("Flags: 0x%x\n", flags);
return result;
}
void RestoreFlagBit(long nBit)
{
if (oldValues[nBit])
oldValues[nBit] = _bittestandset(&flags, nBit);
else
oldValues[nBit] = _bittestandreset(&flags, nBit);
printf_s("Flags: 0x%x\n", flags);
}
unsigned char ToggleBit(long nBit)
{
unsigned char result = _bittestandcomplement(&flags, nBit);
printf_s("Flags: 0x%x\n", flags);
return result;
}
};
int main()
{
Flags f;
f.SetFlagBit(1);
f.SetFlagBit(2);
f.SetFlagBit(3);
f.ClearFlagBit(3);
f.ToggleBit(1);
f.RestoreFlagBit(2);
}
Output
Flags: 0x2 Flags: 0x6 Flags: 0xe Flags: 0x6 Flags: 0x4 Flags: 0x0