lib/ntdll/nasm/rtl/i386_RtlZeroMemory.asm

   1 ; *
   2 ; * COPYRIGHT:       See COPYING in the top level directory
   3 ; * PROJECT:         ReactOS kernel
   4 ; * FILE:            i386_RtlZeroMemory.asm
   5 ; * PURPOSE:         Memory functions
   6 ; * PROGRAMMER:      Magnus Olsen (magnusolsen@greatlord.com)
   7 ; * UPDATE HISTORY:
   8 ; *                  Created 20/07-2003
   9 ; *
  10
  11
  12           BITS 32
  13         GLOBAL _RtlZeroMemory@8         ; (no bug) (max optimze code)
  14           SECTION .text
  15
  16 ; *
  17 ; * [1] VOID STDCALL RtlZeroMemory (PVOID Destination, ULONG Length);
  18 ; *
  19
  20 _RtlZeroMemory@8:
  21
  22         mov ecx,dword [esp + 8 ]               ; Length
  23         cmp ecx,0                              ; if (Length==0) goto .zero
  24           je  .zero
  25
  26         pushad                                 ; Save all register on the stack
  27         mov edi, dword [esp + (4 + 32)]        ; Destination
  28         xor eax,eax                            ; ZeroFillByte = 0
  29
  30
  31
  32 ; code for take four byte each time it loop
  33       mov ebx,ecx                              ; temp_Length = Length
  34       shr ecx,2                                ; Length = Length / sizeof(ULONG)
  35       jz .1byte                                ; if (Length==0) goto .1byte
  36
  37       shl ecx,2                                ; Length = Length * sizeof(ULONG)
  38       sub ebx,ecx                              ; temp_Length = temp_Length - Length;
  39       jz .4bytes                               ; if (temp_Length==0) goto .4byte
  40
  41 ; move 4byte and 1byte
  42       shr ecx,2                                ; Length = Length / sizeof(ULONG)
  43       cld                                      ; clear d flag
  44       rep stosd                                ; while (Length!=0) { (ULONG *) Destination[Length-1]=ZeroFillByte; Legnth = Legnth - 1 }
  45       mov ecx,ebx                              ; Length = temp_Length
  46       rep stosb                                ; while (Length!=0) { (UCHAR *) Destination[Length-1]=ZeroFillByte; Legnth = Legnth - 1 }
  47       popad                                    ; restore register
  48       ret 8                                    ; return
  49
  50 ; move 1byte
  51 .1byte:
  52        mov ecx,dword [esp + (12 +32) ]        ; Length
  53        cld                                    ; clear d flag
  54        rep stosb                              ; while (Length!=0) { (UCHAR *) Destination[Length-1]=ZeroFillByte; Legnth = Legnth - 1 }
  55        popad                                  ; restore register
  56        ret 8                                  ; return
  57
  58 ; move 4bytes
  59 .4bytes:
  60        shr ecx,2                              ; Length = Length / sizeof(ULONG)
  61        cld                                    ; clear d flag
  62        rep stosd                              ; while (Length!=0) { (ULONG *) Destination[Length-1]=ZeroFillByte; Legnth = Legnth - 1 }
  63        popad                                  ; restore register
  64 .zero:
  65        ret 8                                  ; return