On 2014-04-06 17:35-0400 Hazen Babcock wrote: > > Hello, > > In the process of converting some of the PLplot demos to Lisp as part of > the cl-plplot project I found that example 29 triggers a floating point > exception. This is not something that a C compiler will normally report, > but you can make it (or at least gcc) more strict about this. I believe > that the problem occurs in the plP_wcpcx() function in src/plcvt.c, > where we attempt to convert -3.917103e+15 to an integer resulting in an > overflow error. > > The easiest way to see this is to pull my fe_demo branch from here: > https://github.com/HazenBabcock/PLplot > > Or you can look at the two files that I modified to demonstrate this issue: > https://github.com/HazenBabcock/PLplot/blob/fe_demo/examples/c/x29c.c > https://github.com/HazenBabcock/PLplot/blob/fe_demo/src/plcvt.c >
Hi Hazen: Obviously, the attempted conversion should generate an integer overflow, but I frankly don't understand why it generates a _floating-point_ exception since clearly -3.917103e+15 is a valid floating-point number. Do you have some mental model for why there was a generated floating-point exception in this case? That question is just to satisfy my curiosity about how you found the issue, and the much more important question is why in the world numbers like -3.917103e+15 are being generated by example 29? One possibility is some variable is unintialized so -3.917103e+15 is just random numerical garbage, but I checked that possibility with valgrind and got the following absolutely clean result: ==19527== Memcheck, a memory error detector ==19527== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al. ==19527== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info ==19527== Command: examples/c/x29c -dev psc -o test.psc ==19527== ==19527== ==19527== HEAP SUMMARY: ==19527== in use at exit: 0 bytes in 0 blocks ==19527== total heap usage: 2,481 allocs, 2,481 frees, 351,494 bytes allocated ==19527== ==19527== All heap blocks were freed -- no leaks are possible ==19527== ==19527== For counts of detected and suppressed errors, rerun with: -v ==19527== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4) plcvt.c contains code for converting between various plot coordinate systems. Please indicate what device you are using since that should affect some of those transformations. plP_wcpcx converts world coordinates to physical device coordinate using the PLINT value of the following transformation plsc->wpxoff + plsc->wpxscl * x where all those values being combined together are PLFLT. It is hard to figure out how an integer physical device coordinate (e.g., pixels) could correspond to -3.917103e+15 so despite the good valgrind result I am still wondering whether you are dealing with numerical garbage of some kind. Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); the Time Ephemerides project (timeephem.sf.net); PLplot scientific plotting software package (plplot.sf.net); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------------ Put Bad Developers to Shame Dominate Development with Jenkins Continuous Integration Continuously Automate Build, Test & Deployment Start a new project now. Try Jenkins in the cloud. http://p.sf.net/sfu/13600_Cloudbees_APR _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
