EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/GetPowerOfTwo.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 #  GetPowerOfTwo.c
  15 #
  16 #Abstract:
  17 #
  18 #  Calculates the largest integer that is both
  19 #  a power of two and less than Input
  20 #
  21 #--*/
  22 #include "EfiBind.h"
  23 #---------------------------------------------------------------------------
  24     .686:
  25     #.MODEL flat,C
  26     .code:
  27
  28 #---------------------------------------------------------------------------
  29 .globl ASM_PFX(GetPowerOfTwo)
  30 #UINT64
  31 #GetPowerOfTwo (
  32 #  IN UINT64   Input
  33 #  )
  34 #/*++
  35 #
  36 #Routine Description:
  37 #
  38 #  Calculates the largest integer that is both
  39 #  a power of two and less than Input
  40 #
  41 #Arguments:
  42 #
  43 #  Input  - value to calculate power of two
  44 #
  45 #Returns:
  46 #
  47 #  the largest integer that is both  a power of
  48 #  two and less than Input
  49 #
  50 #--*/
  51 ASM_PFX(GetPowerOfTwo):
  52     xorl    %eax, %eax
  53     movl    %eax, %edx
  54     movl    8(%esp), %ecx  # dword ptr Input[4]
  55     jecxz   _F
  56     bsrl    %ecx, %ecx
  57     btsl    %ecx, %edx
  58     jmp     _Exit
  59 _F:
  60     movl    4(%esp), %ecx  # dword ptr Input[0]
  61     jecxz   _Exit
  62     bsrl    %ecx, %ecx
  63     btsl    %ecx, %eax
  64 _Exit:
  65
  66     ret
  67 #GetPowerOfTwo ENDP
  68