From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT edu DOT ar>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: FYI: speed of Allegro/DJGPP
Date: 23 Oct 1997 07:03:10 GMT
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"Alan M. Doerhoefer" wrote:

> This is my testament to the speed of DJGPP and Allegro:
> 
[Sniped history about the fractal viewer]
>         
> So I set out to make a version faster than my Allegro version. I 
> experimented with my old Borland C++ 3.0 and TASM 3.0. 
:-)), bad idea, I think the slow thing is the fractal calculus, not the screen. 
You can get over than 70 fps for a simple blit.

> I wrote
> my own TASM routine to write directly to VGA in Mode 13 and linked
> it to C code identical to my Allegro version except for putpixel.
> Then I tried different combinations of optimizing levels and or 
> inline assembler. I even wrote a Mode X version just for fun. 
> Here is my inline asm for Mode 13h: (thanks A. LaMothe)
> 
>         asm {    
>                  mov     di, 0a000h
>                  mov     es, di
>                  mov     di, y
>                  shl     di, 6
>                  mov     bx, di
>                  shl     di, 2
>                  add     di, bx
>                  add     di, x
>                  mov     al, BYTE PTR color
>                  mov     es:[di], al
>         }
> 
> All tests done on my Pentium 100 and the same CL-5434 graphics board:
> frac with Win32:                200 + seconds
> frac with bcc, tasm, Mode X     25 seconds
> frac with bcc, tasm, Mode 13h   14 seconds
> frac with DJGPP,Allegro,Mode X  7 seconds
> 
> Allegro and DJGPP are FAST, at least under these circumstances.
> Does anyone know where all this speed is coming from? 
Yes, the optimizer.

> I assume
> it is mainly because of two reasons: 1.) The latest DJGPP gcc is
> 32 bit & well optimized for the 486 
True.

> 2.) Allegro's putpixel is well written.
Yes, but the compiler (GCC) can make a better version of putpixel than you 
;-)). Your real mode version is not so good.

You can't compare the code generated by the old BC++ 3.0 with DJGPP. GCC 
optimize much better.

SET 
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