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

   1 /*++
   2
   3 Copyright (c) 2006, Intel Corporation
   4 All rights reserved. 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 #include "Tiano.h"
  23
  24 UINT8
  25 Log2 (
  26   IN UINT64   Operand
  27   )
  28 /*++
  29
  30 Routine Description:
  31
  32   Calculates and floors logarithms based on 2
  33
  34 Arguments:
  35
  36   Operand - value to calculate logarithm
  37
  38 Returns:
  39
  40   The largest integer that is less than or equal
  41   to the logarithm of Operand based on 2
  42
  43 --*/
  44 {
  45   __asm {
  46   mov    ecx, 64
  47
  48   cmp    dword ptr Operand[0], 0
  49   jne    _Log2_Wend
  50   cmp    dword ptr Operand[4], 0
  51   jne    _Log2_Wend
  52   mov    cl, 0FFH
  53   jmp    _Log2_Done
  54
  55 _Log2_Wend:
  56   dec    ecx
  57   cmp    ecx, 32
  58   jae    _Log2_Higher
  59   bt     dword ptr Operand[0], ecx
  60   jmp    _Log2_Bit
  61
  62 _Log2_Higher:
  63   mov    eax, ecx
  64   sub    eax, 32
  65   bt     dword ptr Operand[4], eax
  66
  67 _Log2_Bit:
  68   jc     _Log2_Done
  69   jmp    _Log2_Wend
  70
  71 _Log2_Done:
  72   mov    al, cl
  73   }
  74 }