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/*++
Copyright (c) 2006, Intel Corporation
All rights reserved. This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution. The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
Module Name:
GetPowerOfTwo.c
Abstract:
Calculates the largest integer that is both
a power of two and less than Input
--*/
#include "Tiano.h"
UINT64
GetPowerOfTwo (
IN UINT64 Input
)
/*++
Routine Description:
Calculates the largest integer that is both
a power of two and less than Input
Arguments:
Input - value to calculate power of two
Returns:
the largest integer that is both a power of
two and less than Input
--*/
{
__asm {
xor eax, eax
mov edx, eax
mov ecx, dword ptr Input[4]
jecxz _F
bsr ecx, ecx
bts edx, ecx
jmp _Exit
_F:
mov ecx, dword ptr Input[0]
jecxz _Exit
bsr ecx, ecx
bts eax, ecx
_Exit:
}
}
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