HighBitSet64.c revision 373ade0eb64a522e45b1b94c15b95fb5ab417c00 
1/** @file
2  Math worker functions.
3
4  Copyright (c) 2006 - 2008, 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
16
17
18#include "BaseLibInternals.h"
19
20/**
21  Returns the bit position of the highest bit set in a 64-bit value. Equivalent
22  to log2(x).
23
24  This function computes the bit position of the highest bit set in the 64-bit
25  value specified by Operand. If Operand is zero, then -1 is returned.
26  Otherwise, a value between 0 and 63 is returned.
27
28  @param  Operand The 64-bit operand to evaluate.
29
30  @retval 0..63   Position of the highest bit set in Operand if found.
31  @retval -1     Operand is zero.
32
33**/
34INTN
35EFIAPI
36HighBitSet64 (
37  IN      UINT64                    Operand
38  )
39{
40  if (Operand == (UINT32)Operand) {
41    //
42    // Operand is just a 32-bit integer
43    //
44    return HighBitSet32 ((UINT32)Operand);
45  }
46
47  //
48  // Operand is really a 64-bit integer
49  //
50  if (sizeof (UINTN) == sizeof (UINT32)) {
51    return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
52  } else {
53    return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
54  }
55}
56