From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@coraid.com>
Date: Mon, 18 Jan 2010 16:55:29 -0500
To: 9fans@9fans.net
Message-ID: <70d68890ae6a19e708a0a3271df814ae@coraid.com>
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Subject floating point puzzle

i'm seeing a crash in in _v2d.  unfortunately, i don't
see how this is happening.

8.out 8535: suicide: sys: fp: stack underflow fppc=0x6397 status=0x81e1 pc=0x63a5

however, acid says that the Vlong passed in was all zeros.  the code generating the
call to _v2d is

	overflow = v > vmax*scale;

where
	uvlong v, vmax;
	double scale;

	v = 0; vmax = 2000; scale =1.;

acid: _v2d:x
_3_ {
_1_ {
	lo	0
	hi	0
}
_2_ {
	lols	0
	loms	0
	hils	0
	hims	0
}
}
acid: stk()
_v2d(x=0x0)+0x87 /sys/src/libc/386/vlrt.c:107
[etc]
_main+0x31 /sys/src/libc/386/main9.s:16
acid: fpr()
F0	0
F1	-Inf
F2	0
F3	0
F4	0
F5	0
F6	0
F7	0
control	0x027f
status	0x0161
tag	0xffff
ip offset	0x00006397
cs selector	0x0023
opcode	0x1920
data operand offset	0x2d48
operand selector	0x001b
acid: regs()
PC	0x000063a5 _v2d+0x87  /sys/src/libc/386/vlrt.c:107
SP	0xdfffedc8 ECODE 0xf01006bd EFLAG 0x00010646
CS	0x00000023 DS	 0x0000001b SS	0x0000001b
GS	0xf010001b FS	 0x0000001b ES	0x0000001b
TRAP	0x00000010 math coprocessor error
AX	0x00000000 BX	0x00000000 CX	0x00000000 DX	0x00027254
DI	0x00041920 SI	0x0004191c BP	0xdfffed94

- erik