__ll_rshift

项目
07/25/2011

Microsoft Specific

Shifts a 64-bit value specified by the first parameter to the right by a number of bits specified by the second parameter.

__int64 __ll_rshift(
   __int64 Mask,
   int nBit
);

Parameters

[in] Mask
The 64-bit integer value to shift right.
[in] nBit
The number of bits to shift, modulo 64 on x64, and modulo 32 on x86.

Return Value

The mask shifted by nBit bits.

Requirements

Intrinsic	Architecture
__ll_rshift	x86, x64

Header file <intrin.h>

Remarks

If the second parameter is greater than 64 on x64 (32 on x86), that number is taken modulo 64 (32 on x86) to determine the number of bits to shift. The ll prefix indicates that this is an operation on long long, another name for __int64, the 64-bit signed integral type.

Example

// ll_rshift.cpp
// compile with: /EHsc
// processor: x86, x64
#include <iostream>
#include <intrin.h>
using namespace std;

#pragma intrinsic(__ll_rshift)

int main()
{
   __int64 Mask = - 0x100;
   int nBit = 4;
   cout << hex << Mask << endl;
   cout << " - " << (- Mask) << endl;
   Mask = __ll_rshift(Mask, nBit);
   cout << hex << Mask << endl;
   cout << " - " << (- Mask) << endl;
}

Output

ffffffffffffff00
 - 100
fffffffffffffff0
 - 10

Note If _ull_rshift has been used, the MSB of the right-shifted value would have been zero, so the desired result would not have been obtained in the case of a negative value.

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