CryptoPkg/Library/IntrinsicLib/Ia32/MathRShiftU64.c

/** @file
  64-bit Math Worker Function.
  The 32-bit versions of C compiler generate calls to library routines
  to handle 64-bit math. These functions use non-standard calling conventions.

Copyright (c) 2014, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent

**/

/*
 * Shifts a 64-bit unsigned value right by a certain number of bits.
 */
__declspec(naked) void __cdecl
_aullshr (
  void
  )
{
  _asm {
    ;
    ; Checking: Only handle 64bit shifting or more
    ;
    cmp     cl, 64
    jae     _Exit

    ;
    ; Handle shifting between 0 and 31 bits
    ;
    cmp     cl, 32
    jae     More32
    shrd    eax, edx, cl
    shr     edx, cl
    ret

    ;
    ; Handle shifting of 32-63 bits
    ;
More32:
    mov     eax, edx
    xor     edx, edx
    and     cl, 31
    shr     eax, cl
    ret

    ;
    ; Invalid number (less  then 32bits), return 0
    ;

_Exit:
    xor     eax, eax
    xor     edx, edx
    ret
  }
}