50889777b5420b1878f8c72bc007b79ec6965290
[mirror_edk2.git] / MdePkg / Library / BaseLib / HighBitSet64.c
1 /** @file
2 Math worker functions.
3
4 Copyright (c) 2006, Intel Corporation<BR>
5 All rights reserved. This program and the accompanying materials
6 are licensed and made available under the terms and conditions of the BSD License
7 which accompanies this distribution. The full text of the license may be found at
8 http://opensource.org/licenses/bsd-license.php
9
10 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
11 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
12
13 **/
14
15 #include "BaseLibInternals.h"
16
17 /**
18 Returns the bit position of the highest bit set in a 64-bit value. Equivalent
19 to log2(x).
20
21 This function computes the bit position of the highest bit set in the 64-bit
22 value specified by Operand. If Operand is zero, then -1 is returned.
23 Otherwise, a value between 0 and 63 is returned.
24
25 @param Operand The 64-bit operand to evaluate.
26
27 @return Position of the highest bit set in Operand if found.
28 @retval -1 Operand is zero.
29
30 **/
31 INTN
32 EFIAPI
33 HighBitSet64 (
34 IN UINT64 Operand
35 )
36 {
37 INTN BitIndex;
38
39 for (BitIndex = -1;
40 Operand != 0;
41 BitIndex++, Operand = RShiftU64 (Operand, 1));
42 return BitIndex;
43 }