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