[Ecls-list] BUG: unexpected FLOATING-POINT-UNDERFLOW on Linux/armhf

[Juan Jose Garcia-Ripoll]

ECL uses tanf() for computing the tangent with single-floats. If you have a
look at the code in ecl/src/c/numbers/tan.d you will find the lines below.
One possibility would be to uncomment safe_tanf() and see whether ECL now
works. If this is the case then we might have to add another switch for
your platform :-/


/*
 * As of 2006-10-13 I found this bug in GLIBC's tanf, which overflows
 * when the argument is pi/4. It is 2008 and this has not yet been
 * solved. Not only that, but if we use tan() on float, GCC automatically
 * and stupidly forces the use of tanf().
 */
#if defined(__amd64__) && defined(__GLIBC__)
static double safe_tanf(double x) { return tan(x); }
#else
# define safe_tanf(x) tanf(x)
#endif



On Thu, Mar 28, 2013 at 11:50 PM, Eric Marsden <eric.marsden at free.fr> wrote:

> Hi,
>
> I have recently acquired a cubieboard, a small ARM Cortex-A8 development
> board (ARM v7, NEON, VFPv3), on which I run the rasbpian Debian
> derivative. It's using GCC 4.6.3 and runs fine under ECL, except for a
> bug in TAN:
>
> ,----
> | ;;; Loading #P"/usr/local/lib/ecl-12.12.1/asdf.fas"
> | ECL (Embeddable Common-Lisp) 12.12.1
> (git:e90ff5a6c720334e0450a107bb0bdc1fd746d5ea)
> | Copyright (C) 1984 Taiichi Yuasa and Masami Hagiya
> | Copyright (C) 1993 Giuseppe Attardi
> | Copyright (C) 2000 Juan J. Garcia-Ripoll
> | ECL is free software, and you are welcome to redistribute it
> | under certain conditions; see file 'Copyright' for details.
> | Type :h for Help.
> | Top level in: #<process TOP-LEVEL>.
> | > (tan (coerce (/ pi 4) 'double-float))
> | 0.9999999999999999d0
> | > (tan (coerce (/ pi 4) 'single-float))
> | Condition of type: FLOATING-POINT-UNDERFLOW
> | #<a FLOATING-POINT-UNDERFLOW>
> `----
>
> A basic C program which prints tan(atan(1)) works fine. What can I do to
> help to debug?
>
> --
> Eric Marsden
>
>
>
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-- 
Instituto de Física Fundamental, CSIC
c/ Serrano, 113b, Madrid 28006 (Spain)
http://juanjose.garciaripoll.googlepages.com
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