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

   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 #include "EfiBind.h" //For ASM_PFX
  24 #---------------------------------------------------------------------------
  25
  26 .globl ASM_PFX(Log2)
  27
  28 #UINT8
  29 #Log2 (
  30 #  IN UINT64   Operand
  31 #  )
  32 #/*++
  33 #
  34 #Routine Description:
  35 #
  36 #  Calculates and floors logarithms based on 2
  37 #
  38 #Arguments:
  39 #
  40 #  Operand - value to calculate logarithm
  41 #
  42 #Returns:
  43 #
  44 #  The largest integer that is less than or equal
  45 #  to the logarithm of Operand based on 2
  46 #
  47 #--*/
  48 ASM_PFX(Log2):
  49   movl   $64, %ecx
  50
  51   cmpl   $0, 4(%esp)             # (UINT32 *(&Operand))
  52   jne    _Log2_Wend
  53   cmpl   $0, 8(%esp)             # (UINT32 *(&Operand)) + 1
  54   jne    _Log2_Wend
  55   movb   $0xFF, %cl
  56   jmp    _Log2_Done
  57
  58 _Log2_Wend:
  59   decl   %ecx
  60   cmpl   $32, %ecx
  61   jae    _Log2_Higher
  62   btl    %ecx, 4(%esp)  # (UINT32 *(&Operand))
  63   jmp    _Log2_Bit
  64
  65 _Log2_Higher:
  66   movl   %ecx, %eax
  67   subl   $32, %eax
  68   btl    %eax, 8(%esp)  # (UINT32 *(&Operand)) + 1
  69
  70 _Log2_Bit:
  71   jc     _Log2_Done
  72   jmp    _Log2_Wend
  73
  74 _Log2_Done:
  75   movb   %cl, %al
  76
  77   ret
  78