Message-ID: <35DF84AC.B28C9CBA@unb.ca>
Date: Sat, 22 Aug 1998 23:55:41 -0300
From: Endlisnis <s257m AT unb DOT ca>
MIME-Version: 1.0
To: george DOT foot AT merton DOT oxford DOT ac DOT uk
CC: djgpp AT delorie DOT com
Subject: Re: VESA: hints, clue but no examples
References: <E0zAL2k-0004UN-00 AT sable DOT ox DOT ac DOT uk>
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George Foot wrote:

> On 22 Aug 98 at 15:35, Endlisnis wrote:
>
> >     Yes.  I've made my own 'setdata' function to use a bunch of _farnspokel calls to quickly write a single
> > value to a bunch of contiguous locations.
>
> For a reasonable number of locations, this would probably be faster
> if you used an inline assembler routine; push ES, load it with the
> selector, load EDI with the offset, EAX with the value and ECX with
> the number of longs, then "rep ; stosl" and finally pop ES back
> again.  Perhaps this:
>
>     inline void flmemset (int selector, int offset, int value, int num_longs)

    This version of your 'flmemset' function allows any arbitrary # of bytes to be written, (not necessarily
multiple of 4).

inline void setdata (int selector, int offset, int value, int num_bytes)
{
 asm (
 "pushl %%es;"
 "movw %%dx, %%es;"
 "cld;"
 "movb %%al, %%ah;"
 "rorl $8, %%eax;"
 "movb %%al, %%ah;"
 "rorl $8, %%eax;"
 "movb %%al, %%ah;"

 "shrl $1, %%ecx;"
 "jnc NoByte;"
 "stosb;"
 "NoByte: ;"
 "shrl $1, %%ecx;"
 "jnc NoWord;"
 "stosw;"
 "NoWord: ;"
 "rep; stosl;"
 "popl %%es "
 : : "c" (num_bytes), "a" (value), "d" (selector), "D" (offset)
 : "%ecx", "%edi" );
 }

BTW, are any of those registers listed in the 'clobbered' list really necessary (in this case)?  Since they are
listed as input registers, then aren't they automatically listed as 'clobbered'?
--
     (\/) Endlisnis (\/)
          s257m AT unb DOT ca
          Endlisnis AT GeoCities DOT com
          Endlis AT nbnet DOT nb DOT ca