EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/Log2.asm

   1 ;/*++
   2 ;
   3 ;Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
   4 ;This program and the accompanying materials
   5 ;are licensed and made available under the terms and conditions of the BSD License
   6 ;which accompanies this distribution.  The full text of the license may be found at
   7 ;http://opensource.org/licenses/bsd-license.php
   8 ;
   9 ;THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 ;WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 ;
  12 ;Module Name:
  13 ;
  14 ;  Log2.c
  15 ;
  16 ;Abstract:
  17 ;
  18 ;  64-bit integer logarithm function for IA-32
  19 ;
  20 ;--*/
  21 ;
  22 ;---------------------------------------------------------------------------
  23     .686
  24     .model  flat,C
  25     .code
  26
  27 ;---------------------------------------------------------------------------
  28
  29 ;UINT8
  30 ;Log2 (
  31 ;  IN UINT64   Operand
  32 ;  )
  33 ;/*++
  34 ;
  35 ;Routine Description:
  36 ;
  37 ;  Calculates and floors logarithms based on 2
  38 ;
  39 ;Arguments:
  40 ;
  41 ;  Operand - value to calculate logarithm
  42 ;
  43 ;Returns:
  44 ;
  45 ;  The largest integer that is less than or equal
  46 ;  to the logarithm of Operand based on 2
  47 ;
  48 ;--*/
  49 Log2 PROC
  50   mov    ecx, 64
  51
  52   cmp    dword ptr [esp + 4], 0  ; (UINT32 *(&Operand))
  53   jne    _Log2_Wend
  54   cmp    dword ptr [esp + 8], 0  ; (UINT32 *(&Operand)) + 1
  55   jne    _Log2_Wend
  56   mov    cl, 0FFH
  57   jmp    _Log2_Done
  58
  59 _Log2_Wend:
  60   dec    ecx
  61   cmp    ecx, 32
  62   jae    _Log2_Higher
  63   bt     [esp + 4], ecx ; (UINT32 *(&Operand))
  64   jmp    _Log2_Bit
  65
  66 _Log2_Higher:
  67   mov    eax, ecx
  68   sub    eax, 32
  69   bt     [esp + 8], eax ; (UINT32 *(&Operand)) + 1
  70
  71 _Log2_Bit:
  72   jc     _Log2_Done
  73   jmp    _Log2_Wend
  74
  75 _Log2_Done:
  76   mov    al, cl
  77
  78   ret
  79
  80         Log2 ENDP
  81         END