On 06/12/2012 08:20 AM, Rich Felker wrote: > To me, the only difference is the pain of replacing them. You cannot > have these bit patterns in an LD80 without your program having invoked > undefined behavior (accessing an object as a type other than its > effective type or one of the allowed exceptions), so there's no > fundamental reason either should handle it. In fact it's conceivable > that machines could exist where even just loading the bit pattern into > a floating point register would generate a signal,
But isnanl() is required to operate in spite of signaling representations (that is, isnanl() need NOT load a bit pattern into a floating point register). > so really od should > be performing the test on the unsigned char[] array *before* > reinterpreting it to LD80 rather than calling a function that takes an > LD80 argument to make the test.. But then you are forcing programs to add #ifdefs and sizeof(long double)==12 checks, instead of letting libc do it for them. That is, testing for an invalid LD80 bit representation is implementation-specific (it depends on the specific hardware and compiler ABI before you even have a long double that can have the invalid representation), but isnanl() is generic - we'd much rather have the generic code do the implementation-specific filtering rather than having to make every client learn the #ifdefs necessary for implementation-specific bit pattern filtering. That said, practicality may win on this one, and you may indeed convince Jim that adding an #ifdef into coreutils' od.c is better than bloating isnanl() for the majority of applications that never convert raw bit patterns into long doubles. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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