_bittest, _bittest64
Microsoft Specific
Generates the bt instruction, which examines the bit in position b of address a, and returns the value of that bit.
unsigned char _bittest(
long *a,
long b
);
unsigned char _bittest64(
__int64 *a,
__int64 b
);
Parameters
- [in] 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 |
|---|---|
_bittest |
x86, IPF, x64 |
_bittest64 |
IPF, x64 |
Header file <intrin.h>
Remarks
On the IPF architecture, the bt instruction is not available, so this intrinsic is a custom function that imitates the behavior of bt. 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
// bittest.cpp
// processor: x86, IPF, x64
#include <stdio.h>
#include <intrin.h>
long num = 78002;
int main()
{
unsigned char bits[32];
long nBit;
printf_s("Number: %d\n", num);
for (nBit = 0; nBit < 31; nBit++)
{
bits[nBit] = _bittest(&num, nBit);
}
printf_s("Binary representation:\n");
while (nBit--)
{
if (bits[nBit])
printf_s("1");
else
printf_s("0");
}
}
Output
Number: 78002 Binary representation: 0000000000000010011000010110010