From: brennan AT mack DOT rt66 DOT com (Brennan "The Rev. Bas" Underwood)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Inline Asm?
Date: 6 Jan 1997 17:12:46 -0700
Organization: Rasterfari
Lines: 38
Message-ID: <5as4du$jd6@mack.rt66.com>
References: <19961231 DOT 204032 DOT 5015 DOT 0 DOT chambersb AT juno DOT com>
NNTP-Posting-Host: mack.rt66.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In article <19961231 DOT 204032 DOT 5015 DOT 0 DOT chambersb AT juno DOT com>,
Benjamin D Chambers <chambersb AT juno DOT com> wrote:
>Well, I spent some time stepping through my program with GDB, and found
>that the following lines caused problems:
>
>cmpl	$0,	%%edx  (This is, of course, in the c file)
>jne	0
>
>Now, to me, this means that if edx is not zero, jump to the label 0
>(which was defined earlier) and, if edx is zero, keep executing as
>normal.  However, when I stepped through this with GDB, I found that no
>matter what value edx held, the loop fell through (that is, no jump was
>performed).  Am I doing something wrong here?  Again, thanx in advance...

Tell you what, just use jnz as below... (JNZ = jump if not zero)

>  asm("0:                                       \n
>        movb    $1,             (,%%eax,1)      \n
>        incl    %%eax                           \n
>        decl    %%edx                           \n
         jnz     0b                              \n
>       "
>  :     // No Output
>  : "d" (size),
>    "a" (data)
>  : "memory", "%cc"
>  );

Also, the decl and jnz will pair into 1 cycle on the Pentium.
And, I put a 'b' on the '0', to make 0 into a local label in case of
loop unrolling.


Brennan
-- 
 brennan AT rt66 DOT com |  "Developing for Windows is not fun." -- John Carmack
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