Re: Floating-point bug reports detected by our tool for the GNU Scientific Library --from madongyu

[Dave Allured - NOAA Affiliate]

Madongyu, if you are publishing a tool to identify bugs, you need to
document your definition of "bug".  To me, bug means unexpected behavior,
loosely speaking.  For example, on a well constructed modern processor, the
result of x = sqrt (-1) is floating point exception.  That is not
unexpected behavior, and it is not a bug.  Furthermore, it is well known
that a negative number is invalid input for this function.  If someone says
this is a problem, then the problem is the invalid input, not the function
itself.

With this in mind, please reevaluate your 8 scenarios.  For each scenario,
please identify whether the function input is clearly valid or invalid.
With that consideration, also identify whether the function behavior is
considered expected or unexpected, in your judgement.


On Wed, Nov 22, 2023 at 6:44 PM 马冬雨 <2021110893@bupt.cn> wrote:

> Dear GSL Developers：
>
>    My name is Madongyu. I have sent a mail yesterday about floating-point
> bug reports detected by our tool for the GNU Scientific Library.
>
>    I add pictures proof of bug results detected by out tool and send them
> to you as attachment in this mail.
>
>    I am a postgraduate student majoring in program analysis of computer
> science at Beijing University of Posts and Telecommunications. My research
> group is developing a symbolic execution tool called YUSE to detect
> floating-point exceptions in numerical code. We've found inputs that cause
> some of the GSL 2.7.1 functions to throw floating-point exceptions. I've
> written this mail to see if you consider any of them(8 results) to be real
> bugs. If you could confirm whether any of these exceptions are useful
> warnings or actual bugs, we would very appreciate it. Because authoritative
> confirmation from GSL Developers to these exceptions is very important for
> us. We will release our tool as open source immediately if GSL Developers
> confirm for us that these are real bugs or useful warnings.
>
> The purpose of our tool is to comprehensively detect floating-point
> exceptions in the program. For each category of floating-point exception we
> found, we listed 1 or 2. We describe the name of function, the type of
> exception thrown, the inputs that trigger the exception, and specific
> location of the code that causes the exception. Category 1：invalid
> operation exception 1.The function gsl_sf_conicalP_xlt1_large_neg_mu_e
> throws an invalid exception when its input tau=1.0, mu=2.0, x=3.0 at line
> 221 in file /gsl-2.7.1/specfunc/legendre_con.c: double p =
> x/sqrt(beta2*(1.0-x*x) + 1.0); Because the parameter of sqrt cannot be
> negative numbers, invalid exception occurs in this occasion.
>
> 2.The function gsl_cdf_laplace_Qinv throws an invalid exception when its
> input Q=-0.5 at line 67 in file /gsl-2.7.1/cdf/laplaceinv.c：x = -a *
> log(2*Q);Because the parameter of log cannot be negative numbers, invalid
> exception occurs in this occasion. Category 2：overflow 3.The function
> gsl_sf_bessel_Knu_scaled_asymp_unif_e throws a overflow exception when its
> input nu=1.45e-192, x=1.0 at line 398 in file
> /gsl-2.7.1/specfunc/bessel.c:  double root_term = hypot(1.0,z);
>
> 4.The function gsl_sf_conicalP_xlt1_large_neg_mu_e throws a overflow
> exception when its input tau =1.23e189,mu=1e-2 at line 219 in file
> /gsl-2.7.1/specfunc/legendre_con.c: double beta2 = beta*beta; Category
> 3：underflow 5.The function gsl_sf_bessel_Jnu_asympx_e throws an underflow
> exception when its input nu=1.23e-189, x=1.0 at line 217 in file
> /gsl-2.7.1/specfunc/bessel.c:  double mu = 4.0*nu*nu; Category
> 4：division-by-zero 6.The function gsl_sf_bessel_Knu_scaled_asympx_e throws
> an division-by-zero floating-point exception when its input x=0.0 at line
> 318 in file /gsl-2.7.1/specfunc/bessel.c: double r = nu/x; Category 5：type
> conversion 7.The function gsl_ran_gamma_knuth throws an overflow caused by
> type conversion exception when its input a=1.23e189 at line 44 in file
> /gsl-2.7.1/randist/gamma.c: unsigned int na = floor (a); Category
> 6：inexact(rounding error) 8.The function hyperg_1F1_1 throws a rounding
> error exception which cause the while loop to not terminate when its input
> b=x=1.23e189 at line 378 in file /gsl-2.7.1/specfunc/hyperg_1F1.c: while(bp
> &gt; b+0.1) {.The loop at 378 will not terminate when x reaches 1.23e189 (a
> very large value),because bp -= 1.0 at line 380 makes bp – 1.0 is rounded
> to bp itself, thus the while condition at bp &gt; b+0.1 at 378 is satisfied
> all the time and can not terminate. I am very sorry about that I have
> disturbed you in your busy schedule. Authoritative confirmation from GSL
> Developers to these exceptions is very important for us. I am looking
> forward to your reply. Thank you very much.
>
> Best wishes
>
> From Madongyu
> Beijing University of Posts and Telecommunications
>