Re: [ros-dev] [ros-diffs] [tkreuzer] 42353: asm version of DIB_32BPP_ColorFill: - Add frame pointer - Get rid of algin_draw, 32bpp surfaces must be DWORD aligned - Optimize the loop - Add comments

[Jose Catena]

Below my C code based on the C code previously shown here, and the assembly
generated by vc.
This function, as most ones, does not benefit much from asm coding, although
some cycles can be saved, most notably inside the loop (a cmp and additional
branch in vc generated code).
Some algorithms can benefit a lot from asm, though. For example the Fletcher
checksum or incrementing/decrementing variables larger than the register
size, where the use of the carry flag can save many cycles. Also when a
function exec time is very critical may deserve asm coding, but I think in
this case it does not worth it, as the saving in percentage is tiny (any
compiler I know will use rep stosd for the inner loop, which has the largest
weight in the total time).

BOOLEAN DIB_32BPP_ColorFill(SURFOBJ* pso, RECTL* prcl, ULONG iColor)
{
    LONG lDelta, cx, cy;
    char * pulLine;

lDelta = pso->lDelta;
    pulLine= (char *)((char *)pso->pvScan0 + prcl->top * lDelta +
(prcl->left << 2));

cx = prcl->right - prcl->left;
    if (cx <= 0)
        return TRUE;

cy = prcl->bottom - prcl->top;
    if (cy <= 0)
        return TRUE;

ULONG *p;
    ULONG c;
    for(; cy--; pulLine += lDelta)
    {
    	for(p = (ULONG *)pulLine, c = cx; c--; )
    	{
    		*p++ = iColor;
    	}
    }

return TRUE;
}

PUBLIC	?DIB_32BPP_ColorFill@@YAEPAU_SURFOBJ@@PAU_RECTL@@K@Z ;
DIB_32BPP_ColorFill
; Function compile flags: /Ogtpy
_TEXT	SEGMENT
?DIB_32BPP_ColorFill@@YAEPAU_SURFOBJ@@PAU_RECTL@@K@Z PROC ;
DIB_32BPP_ColorFill
; Line 52
    mov	ecx, DWORD PTR ds:4
; Line 54
    mov	edx, DWORD PTR ds:8
    push	ebp
    mov	ebp, DWORD PTR ds:36
    imul	ecx, ebp
    xor	eax, eax
    mov	eax, DWORD PTR [eax]
    push	esi
    lea	esi, DWORD PTR [ecx+eax*4]
    add	esi, DWORD PTR ds:32
    sub	edx, eax
; Line 55
    test	edx, edx
; Line 56
    jle	SHORT $LN22@DIB_32BPP_
    push	ebx
; Line 58
    mov	ebx, DWORD PTR ds:12
    sub	ebx, DWORD PTR ds:4
; Line 59
    test	ebx, ebx
; Line 60
    jle	SHORT $LN21@DIB_32BPP_
    push	edi
    npad	4
$LL18@DIB_32BPP_:
; Line 64
    dec	ebx
; Line 66
    test	edx, edx
    je	SHORT $LN2@DIB_32BPP_
    mov	ecx, edx
    xor	eax, eax
    mov	edi, esi
    rep stosd
$LN2@DIB_32BPP_:
    add	esi, ebp
    test	ebx, ebx
    jne	SHORT $LL18@DIB_32BPP_
    pop	edi
$LN21@DIB_32BPP_:
    pop	ebx
$LN22@DIB_32BPP_:
    pop	esi
; Line 72
    mov	al, 1
    pop	ebp
; Line 73
    ret	0
?DIB_32BPP_ColorFill@@YAEPAU_SURFOBJ@@PAU_RECTL@@K@Z ENDP ;
DIB_32BPP_ColorFill

In asm I would write the loop as:
    mov eax, iColor	
    mov ebx, pulLine
    mov edx, cy
L1:
    mov di, bx
    mov cx, _cx
    rep stosd
    add dx, lDelta
    dec dx
    jnz l1

Jose Catena
DIGIWAVES S.L.