Optimized HighBitSetXX() functions
[mirror_edk2.git] / MdePkg / Library / BaseLib / HighBitSet32.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 32-bit value. Equivalent
19 to log2(x).
20
21 This function computes the bit position of the highest bit set in the 32-bit
22 value specified by Operand. If Operand is zero, then -1 is returned.
23 Otherwise, a value between 0 and 31 is returned.
24
25 @param Operand The 32-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 HighBitSet32 (
34 IN UINT32 Operand
35 )
36 {
37 INTN BitIndex;
38
39 if (Operand == 0) {
40 return - 1;
41 }
42 for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
43 return BitIndex;
44 }