On Tue, 2010-06-15 at 13:28 +0100, Paulo J. Matos wrote: > Hi all, > > I am implementing some function for conversion between modes (QI -> > HF, SF -> HI, etc). For this it would be useful to know the floating > point representation using in libgcc. However, I can't find any > description of it anywhere. Is it using IEEE floating point > representation?
I might be very wrong (back-ends & floating points are things I don't really know much about), but I would imagine that libgcc implement the minimal runtime code -used to run your applications compiled by GCC- useful for floating point. If this is true, then libgcc implement the floating point number as provided, supported, or suggested by the target hardware & system [which is different on Vax & on x86, for instance]. Within the GCC compiler, floating points are represented by the struct real_value defined in gcc/real.h, and not by the native double numbers of the host system (the one running GCC). This is probably needed to permit bizarre GCC uses like cross-compiling from an IBM Serie Z (the successor to IBM 370 etc.) to e.g. a Dec Alpha. Of course, most GCC users probably run it on some x86 under Linux or Cygwin (and perhaps cross-compile for an ARM target), but GCC is designed to support very strange hosts & targets, in particular systems with non IEEE 754 floating point numbers. Cheers. -- Basile STARYNKEVITCH http://starynkevitch.net/Basile/ email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359 8, rue de la Faiencerie, 92340 Bourg La Reine, France *** opinions {are only mines, sont seulement les miennes} ***
