HighBitSet64.c revision e1f414b6a7d8a0424e0e01f655b09a4612b4d0e8 
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//
16// Include common header file for this module.
17//
18#include "CommonHeader.h"
19
20#include "BaseLibInternals.h"
21
22/**
23  Returns the bit position of the highest bit set in a 64-bit value. Equivalent
24  to log2(x).
25
26  This function computes the bit position of the highest bit set in the 64-bit
27  value specified by Operand. If Operand is zero, then -1 is returned.
28  Otherwise, a value between 0 and 63 is returned.
29
30  @param  Operand The 64-bit operand to evaluate.
31
32  @return Position of the highest bit set in Operand if found.
33  @retval -1  Operand is zero.
34
35**/
36INTN
37EFIAPI
38HighBitSet64 (
39  IN      UINT64                    Operand
40  )
41{
42  if (Operand == (UINT32)Operand) {
43    //
44    // Operand is just a 32-bit integer
45    //
46    return HighBitSet32 ((UINT32)Operand);
47  }
48
49  //
50  // Operand is really a 64-bit integer
51  //
52  if (sizeof (UINTN) == sizeof (UINT32)) {
53    return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
54  } else {
55    return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
56  }
57}
58