__popcnt16, __popcnt, __popcnt64
Microsoft Specific
Counts the number of 1 bits (population count) in a 16-, 32-, or 64-bit unsigned integer.
Syntax
unsigned short __popcnt16(
unsigned short value
);
unsigned int __popcnt(
unsigned int value
);
unsigned __int64 __popcnt64(
unsigned __int64 value
);
Parameters
value
[in] The 16-, 32-, or 64-bit unsigned integer for which we want the population count.
Return value
The number of 1 bits in the value parameter.
Requirements
| Intrinsic | Architecture |
|---|---|
__popcnt16 |
Advanced Bit Manipulation |
__popcnt |
Advanced Bit Manipulation |
__popcnt64 |
Advanced Bit Manipulation in 64-bit mode. |
Header file <intrin.h>
Remarks
Each of the intrinsics generates the popcnt instruction. In 32-bit mode, there are no 64-bit general-purpose registers, so 64-bit popcnt isn't supported.
To determine hardware support for the popcnt instruction, call the __cpuid intrinsic with InfoType=0x00000001 and check bit 23 of CPUInfo[2] (ECX). This bit is 1 if the instruction is supported, and 0 otherwise. If you run code that uses these intrinsics on hardware that doesn't support the popcnt instruction, the results are unpredictable.
Example
#include <iostream>
#include <intrin.h>
using namespace std;
int main()
{
unsigned short us[3] = {0, 0xFF, 0xFFFF};
unsigned short usr;
unsigned int ui[4] = {0, 0xFF, 0xFFFF, 0xFFFFFFFF};
unsigned int uir;
for (int i=0; i<3; i++) {
usr = __popcnt16(us[i]);
cout << "__popcnt16(0x" << hex << us[i] << ") = " << dec << usr << endl;
}
for (int i=0; i<4; i++) {
uir = __popcnt(ui[i]);
cout << "__popcnt(0x" << hex << ui[i] << ") = " << dec << uir << endl;
}
}
__popcnt16(0x0) = 0
__popcnt16(0xff) = 8
__popcnt16(0xffff) = 16
__popcnt(0x0) = 0
__popcnt(0xff) = 8
__popcnt(0xffff) = 16
__popcnt(0xffffffff) = 32
END Microsoft Specific
Portions Copyright 2007 by Advanced Micro Devices, Inc. All rights reserved. Reproduced with permission from Advanced Micro Devices, Inc.