zeromemory_asm.s

来自「一个类似windows」· S 代码 · 共 62 行

/* 
 * COPYRIGHT:       See COPYING in the top level directory
 * PROJECT:         ReactOS kernel
 * FILE:            zeromemory_asm.S
 * PURPOSE:         Memory functions
 * PROGRAMMERS:     Patrick Baggett ([e-mail])
 *                  Alex Ionescu ([e-mail])
 *                  Magnus Olsen ([e-mail])
 */

.intel_syntax noprefix

/* GLOBALS ****************************************************************/

.globl  _RtlZeroMemory@8          // (no bug) (max optimze code)

/* FUNCTIONS ***************************************************************/

_RtlZeroMemory@8:     
    mov ecx,dword [esp + 8 ]     // Length     
    cmp ecx,0// if (Length==0) goto .zero  
	je 3f	        

    pushad   // Save all register on the stack      
    mov edi, dword [esp + (4 + 32)]        // Destination 
    xor eax,eax        // ZeroFillByte = 0

// code for take four byte each time it loop
    mov ebx,ecx        // temp_Length = Length    
    shr ecx,2// Length = Length / sizeof(ULONG)      
    jz 1f    // if (Length==0) goto .1byte
       
    shl ecx,2// Length = Length * sizeof(ULONG)  
    sub ebx,ecx        // temp_Length = temp_Length - Length// 
    jz 2f    // if (temp_Length==0) goto .4byte

// move 4byte and 1byte
    shr ecx,2// Length = Length / sizeof(ULONG)      
    cld      // clear d flag 
    rep stosd// while (Length!=0) { (ULONG *) Destination[Length-1]=ZeroFillByte// Legnth = Legnth - 1 }  
    mov ecx,ebx        // Length = temp_Length 
    rep stosb// while (Length!=0) { (UCHAR *) Destination[Length-1]=ZeroFillByte// Legnth = Legnth - 1 }  
    popad    // restore register 
    ret 8    // return  
     
// move 1byte  
1: 
    mov ecx,dword [esp + (12 +32) ]        // Length       
    cld      // clear d flag 
    rep stosb// while (Length!=0) { (UCHAR *) Destination[Length-1]=ZeroFillByte// Legnth = Legnth - 1 }
    popad    // restore register
    ret 8    // return

// move 4bytes     
2:
    shr ecx,2// Length = Length / sizeof(ULONG)      
    cld      // clear d flag 
    rep stosd// while (Length!=0) { (ULONG *) Destination[Length-1]=ZeroFillByte// Legnth = Legnth - 1 } 
    popad    // restore register 
3:
    ret 8    // return