CryptoPkg/Library/IntrinsicLib/Ia32/MathRShiftU64.c

   1 /** @file
   2   64-bit Math Worker Function.
   3   The 32-bit versions of C compiler generate calls to library routines
   4   to handle 64-bit math. These functions use non-standard calling conventions.
   5
   6 Copyright (c) 2014, Intel Corporation. All rights reserved.<BR>
   7 This program and the accompanying materials
   8 are licensed and made available under the terms and conditions of the BSD License
   9 which accompanies this distribution.  The full text of the license may be found at
  10 http://opensource.org/licenses/bsd-license.php
  11
  12 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  13 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  14
  15 **/
  16
  17
  18 /*
  19  * Shifts a 64-bit unsigned value right by a certain number of bits.
  20  */
  21 __declspec(naked) void __cdecl _aullshr (void)
  22 {
  23   _asm {
  24     ;
  25     ; Checking: Only handle 64bit shifting or more
  26     ;
  27     cmp     cl, 64
  28     jae     _Exit
  29
  30     ;
  31     ; Handle shifting between 0 and 31 bits
  32     ;
  33     cmp     cl, 32
  34     jae     More32
  35     shrd    eax, edx, cl
  36     shr     edx, cl
  37     ret
  38
  39     ;
  40     ; Handle shifting of 32-63 bits
  41     ;
  42 More32:
  43     mov     eax, edx
  44     xor     edx, edx
  45     and     cl, 31
  46     shr     eax, cl
  47     ret
  48
  49     ;
  50     ; Invalid number (less then 32bits), return 0
  51     ;
  52 _Exit:
  53     xor     eax, eax
  54     xor     edx, edx
  55     ret
  56   }
  57 }