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/*++
Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
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:
Log2.c
Abstract:
64-bit integer logarithm function for IA-32
--*/
#include "Tiano.h"
UINT8
Log2 (
IN UINT64 Operand
)
/*++
Routine Description:
Calculates and floors logarithms based on 2
Arguments:
Operand - value to calculate logarithm
Returns:
The largest integer that is less than or equal
to the logarithm of Operand based on 2
--*/
{
__asm {
mov ecx, 64
cmp dword ptr Operand[0], 0
jne _Log2_Wend
cmp dword ptr Operand[4], 0
jne _Log2_Wend
mov cl, 0FFH
jmp _Log2_Done
_Log2_Wend:
dec ecx
cmp ecx, 32
jae _Log2_Higher
bt dword ptr Operand[0], ecx
jmp _Log2_Bit
_Log2_Higher:
mov eax, ecx
sub eax, 32
bt dword ptr Operand[4], eax
_Log2_Bit:
jc _Log2_Done
jmp _Log2_Wend
_Log2_Done:
mov al, cl
}
}
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