From:	XXguille AT XXiies DOT XXes (Guillermo Rodriguez Garcia)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: mouse problem!
Date:	Fri, 28 May 1999 10:59:16 GMT
Organization:	Telefonica Transmision de Datos
Lines:	37
Message-ID:	<374df1b6.2220679@noticias.iies.es>
References:	<7ikl66$gal$1 AT nnrp1 DOT deja DOT com>
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To:	djgpp AT delorie DOT com
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El día Thu, 27 May 1999 23:40:54 GMT, nj210337 AT stmail DOT staffs DOT ac DOT uk
escribió:

> *xinc = (int)regs.w.cx;
> *yinc = (int)regs.w.dx;

Just change these casts to

*xinc = (short)regs.w.cx;
*yinc = (short)regs.w.dx;

Because the previous one says to the compiler "interpret this 16-bit
value as if it (already) was an int" (so it doesn't expand sign to
32-bit). And what it should say is "interpret this 16-bit value as
being a signed short, so please expand it to a 32-bit int and of
course pay attention to the sign".

Test this:

#include <stdio.h>
int main (void)
{
	unsigned short x = 0xFFFF;
	int a, b;

	a = (int)x;	/* wrong */
	b = (short)x; /* right */

	printf("Look: %d %d", a, b);
	return 0;
}

Regards,
GUILLE
----
Guillermo Rodriguez Garcia
XXguille AT XXiies DOT XXes (ya sabes :-)

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