Implementation of memcpy and memmove Functions

Memcpy

Code:
;***
; Memcpy. ASM-contains memcpy and memmove routines
;
; Copyright (c) 1986-1997, Microsoft Corporation. All right reserved.
;
; Purpose:
; Memcpy () copies a source memory buffer to a destination buffer.
; Overlapping buffers are not treated specially, so propogation may occur.
; Memmove () copies a source memory buffer to a destination buffer.
; Overlapping buffers are treated specially, to avoid propogation.
;
; **************************************** ***************************************
;***
; Memcpy-copy source buffer to destination Buffer
;
; Purpose:
; Memcpy () copies a source memory buffer to a destination memory buffer.
; This routine does not recognize overlapping buffers, and thus can lead
; To propogation.
; For cases where propogation must be avoided, memmove () must be used.
;
; Algorithm:

Void * memcpy (void * DEST, void * Source, size_t count)

{

Void * ret = DEST;

// Copy from lower address to higher address

While (count --)

* DEST ++ = * source;

 

Return ret;

}

 

 

Memmove

Memmove-copy source buffer to destination Buffer
;
; Purpose:
; Memmove () copies a source memory buffer to a destination memory buffer.
; This routine recognize overlapping buffers to avoid propogation.
; For cases where propogation is not a problem, memcpy () can be used.
;
; Algorithm:

Void * memmove (void * DEST, void * Source, size_t count)

{

Void * ret = DEST;

 

If (DEST <= source | DEST> = (source + count ))

{

// Non-overlapping Buffers
// Copy from lower addresses to higher addresses

While (count --)

* DEST ++ = * Source ++;

}

Else

{

// Overlapping Buffers
// Copy from higher addresses to lower addresses

 

DeST + = count-1;

Source + = count-1;

While (count --)

* Dest -- = * source --; L

}

Return ret;

}

 

Another implementation:

Void * mymemcpy (void * DEST, const void * SRC, size_t count)
{
Char * D = (char *) DEST;
Const char * s = (const char *) SRC;
// Int n = (count + 7)/8; // count> 0 assumed
Int n = count> 3;
Switch (count & 7)
{
Do {* D ++ = * s ++;
Case 7: * D ++ = * s ++;
Case 6: * D ++ = * s ++;
Case 5: * D ++ = * s ++;
Case 4: * D ++ = * s ++;
Case 3: * D ++ = * s ++;
Case 2: * D ++ = * s ++;
Case 1: * D ++ = * s ++;
Case 0} // while (-- N> 0 );
While (n --> 0)
}

Return DEST;
}