From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <b974470c3e357a7efd16b8345fb68e94@orthanc.cc.titech.ac.jp>
To: 9fans@cse.psu.edu
From: YAMANASHI Takeshi <uncover@beat.cc.titech.ac.jp>
Date: Thu,  1 Jul 2004 13:50:35 +0900
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Subject: [9fans] fp: stack underflow error
Topicbox-Message-UUID: b23a4c1e-eacd-11e9-9e20-41e7f4b1d025

I encountered a "sys: fp: stack underflow" error in my program.
When I change the uint arguments of a2b() to int, the modified program
ran successfully.  What's wrong with my program?

Thanks in advance.

++ program and acid stack trace are attached below ++

% nashi@valinore cat suflow.c
#include <u.h>
#include <libc.h>

/*{
	8c suflow.c; 8l suflow.8; ./8.out
}*/

ulong
a2b(uint fr, uint fg, uint fb, uint tr, uint tg, uint tb, double dis)
{
	uchar r, g, b;

	r = fr + (tr - fr)*dis;
	g = fg + (tg - fg)*dis;
	b = fb + (tb - fb)*dis;

	return (r<<24)+(g<<16)+(b<<8)+0xFF;
}

void
main()
{
	int i;
	ulong p;

	for(i=0; i<256; i++)
		p=a2b(0, 0, 0xFF, 00, 0xFF, 00, 2.0*i/256.0);
	exits(nil);
}



% nashi@valinore ./8.out
8.out 1167: suicide: sys: fp: stack underflow fppc=0x1118 status=0x80a1 pc=0x0000118f


% nashi@valinore acid 1167
/proc/1167/text:386 plan 9 executable

/sys/lib/acid/port
/sys/lib/acid/386
acid: stk()
At pc:0x0000118f:main+0x46 /usr/nashi/src/test/suflow.c:27
main() /usr/nashi/src/test/suflow.c:21
	called from _main+0x31 /sys/src/libc/386/main9.s:16

--