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 SPDX-License-Identifier: BSD-2-Clause-Patent
   8
   9 **/
  10
  11 /*
  12  * Shifts a 64-bit unsigned value right by a certain number of bits.
  13  */
  14 __declspec(naked) void __cdecl
  15 _aullshr (
  16   void
  17   )
  18 {
  19   _asm {
  20     ;
  21     ; Checking: Only handle 64bit shifting or more
  22     ;
  23     cmp     cl, 64
  24     jae     _Exit
  25
  26     ;
  27     ; Handle shifting between 0 and 31 bits
  28     ;
  29     cmp     cl, 32
  30     jae     More32
  31     shrd    eax, edx, cl
  32     shr     edx, cl
  33     ret
  34
  35     ;
  36     ; Handle shifting of 32-63 bits
  37     ;
  38 More32:
  39     mov     eax, edx
  40     xor     edx, edx
  41     and     cl, 31
  42     shr     eax, cl
  43     ret
  44
  45     ;
  46     ; Invalid number (less  then 32bits), return 0
  47     ;
  48
  49 _Exit:
  50     xor     eax, eax
  51     xor     edx, edx
  52     ret
  53   }
  54 }