Patrick Palka
6d9dbdf51f
The fallback implementation of floating-point std::from_chars (used for formats other than binary32/64) just calls the C library's strtod family of functions. In case of overflow, the behavior of these functions is rigidly specified: If the correct value overflows and default rounding is in effect, plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return type and sign of the value), and the value of the macro ERANGE is stored in errno. But in case of underflow, implementations are given more leeway: If the result underflows the functions return a value whose magnitude is no greater than the smallest normalized positive number in the return type; whether errno acquires the value ERANGE is implementation-defined. Thus the fallback implementation can (and does) portably detect overflow, but it can't portably detect underflow. However, glibc (and presumably other high-quality C library implementations) will reliably set errno to ERANGE in case of underflow as well, and it'll also return the nearest denormal number to the correct value (zero in case of true underflow), which allows callers to succesfully parse denormal numbers. So since we can't be perfect here, this patch takes the best effort approach of assuming a high quality C library implementation with respect to this underflow behavior, and refines our implementation to try to distiguish between a denormal result and true underflow by inspecting strtod's return value. libstdc++-v3/ChangeLog: * src/c++17/floating_from_chars.cc (from_chars_impl): In the ERANGE case, distinguish between a denormal result and true underflow by checking if the return value is 0.
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.