From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <d66164ffbf07b27c99685ea41599f1a3@vitanuova.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] fp: stack underflow error
Date: Thu,  1 Jul 2004 20:24:23 +0100
From: rog@vitanuova.com
In-Reply-To: <b974470c3e357a7efd16b8345fb68e94@orthanc.cc.titech.ac.jp>
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> I encountered a "sys: fp: stack underflow" error in my program.

looks like a compiler bug.

here's a simpler version of the code that does the same thing.
who'd've thought that a2b() would generate such
convoluted code? what's that comparison for?

	TEXT	a2b+0(SB),0,$12
	MOVL	tb+4(FP),CX
	SUBL	fb+0(FP),CX
	MOVL	CX,.safe+-4(SP)
	FMOVL	.safe+-4(SP),F0
	CMPL	CX,$0
	JGE	,2(PC)
	FADDD	$(4.29496729600000000e+09),F0
	FMULD	dis+8(FP),F0
	FSTCW	,.safe+-8(SP)
	MOVW	$3967,.safe+-6(SP)
	FLDCW	.safe+-6(SP),
	FMOVLP	F0,.safe+-4(SP)
	FLDCW	.safe+-8(SP),
	MOVL	.safe+-4(SP),AX
	RET	,

#include <u.h>
#include <libc.h>
int
a2b(int fb, uint tb, double dis)
{
	return (tb - fb)*dis;
}

void
main(void)
{
	a2b(1, 0, 65);
	a2b(1, 0, 66);
}