Sender:	nate AT cartsys DOT com
Message-ID:	<36EC443E.EFFA47B5@cartsys.com>
Date:	Sun, 14 Mar 1999 15:20:30 -0800
From:	Nate Eldredge <nate AT cartsys DOT com>
X-Mailer:	Mozilla 4.08 [en] (X11; I; Linux 2.2.3 i586)
MIME-Version:	1.0
To:	djgpp AT delorie DOT com
CC:	djgpp-workers AT delorie DOT com
Subject:	Re: sin(acos((float)i/1024))*0x10000L
References:	<199903142305 DOT RAA16482 AT x15 DOT dejanews DOT com>
Reply-To:	djgpp-workers AT delorie DOT com

The Beyonder <beyonder69 AT geocities DOT com> wrote:


> Hi Y'all,
> after visiting a site on how to draw primitive shapes to the screen, I
> decided to try this circle technique.  It said to first generate a
> trigonomitry table full of sin_acos info?  So I copied his source code:
[snip]
> Now during compilation it just gets stuck on "Generating Tri table...".
> SIN alone works, and so does COS... but ACOS alone just stalls (I can
> quit using CTRL-C).
> 
> Is it ACOS or my programming?

This appears to be a bug in the FPU emulation.  I can reproduce it on an
FPU-less machine; any call to `acos' appears to enter some kind of
infinite loop.  I hit Ctrl-Break and was rewarded with this traceback
(here symified):

Exiting due to signal SIGINT
Control-Break Pressed at eip=00092d6b
eax=01000400 ebx=ffff8000 ecx=01000400 edx=00000000 esi=ffff8000
edi=ffffc000
ebp=0008f238 esp=0008f1ec program=A:\ACOS-TES.EXE
cs: sel=00a7  base=10000000  limit=0009ffff
ds: sel=00af  base=10000000  limit=0009ffff
es: sel=00af  base=10000000  limit=0009ffff
fs: sel=008f  base=0000fdb0  limit=0000ffff
gs: sel=00bf  base=00000000  limit=0010ffff
ss: sel=00af  base=10000000  limit=0009ffff
App stack: [0008f308..0000f308]  Exceptn stack: [0000f1f0..0000d2b0]
 
Call frame traceback EIPs:
  0x00092d6b   0x92d6b
  0x00093213   0x93213
  0x0009524b   0x9524b
  0x0000269c   ___frame_state_for+328
  0x000041b3   _raise+99
  0x000041fa   ___djgpp_exception_processor+26
  0x00000001   0x1
  0x00002d3a   ___crt1_startup+174

Looks somewhat unusual.

To the original poster: As a workaround, add `-lm' to your link command
line.  This uses a different implementation of the math functions that
seems to work better.  You might also try installing WMEMU (I didn't try
this); see FAQ section 11.1.
-- 

Nate Eldredge
nate AT cartsys DOT com

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