divu64x32.c

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/*++

Copyright (c) 2006, Intel Corporation                                                         
All rights reserved. This program and the accompanying materials                          
are licensed and made available under the terms and conditions of the BSD License         
which accompanies this distribution.  The full text of the license may be found at        
http://opensource.org/licenses/bsd-license.php                                            
                                                                                          
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             

Module Name:

  DivU64x32.c

Abstract:

  64-bit division function for IA-32

--*/

#include "Tiano.h"

UINT64
DivU64x32 (
  IN UINT64   Dividend,
  IN UINTN    Divisor,
  OUT UINTN   *Remainder OPTIONAL
  )
/*++

Routine Description:

  This routine allows a 64 bit value to be divided with a 32 bit value returns 
  64bit result and the Remainder.

Arguments:

  Dividend  - dividend
  Divisor   - divisor
  Remainder - buffer for remainder
  
Returns:

  Dividend  / Divisor
  Remainder = Dividend mod Divisor
  
N.B. only works for 31bit divisors!!

--*/
{
  __asm {
  ;
  ; let edx contain the intermediate result of remainder
  ;
  xor    edx, edx
  mov    ecx, 64
  
_DivU64x32_Wend:
  shl    dword ptr Dividend[0], 1
  rcl    dword ptr Dividend[4], 1    
  rcl    edx, 1            

  ;
  ; If intermediate result of remainder is larger than
  ; or equal to divisor, then set the lowest bit of dividend,
  ; and subtract divisor from intermediate remainder
  ;
  cmp    edx, Divisor                
  jb     _DivU64x32_Cont
  bts    dword ptr Dividend[0], 0            
  sub    edx, Divisor
                   
_DivU64x32_Cont:
  loop   _DivU64x32_Wend

  cmp    Remainder, 0
  je     _DivU64x32_Done
  mov    eax, Remainder
  mov    dword ptr [eax], edx

_DivU64x32_Done:
  mov    eax, dword ptr Dividend[0]
  mov    edx, dword ptr Dividend[4]
  }
}