On Wed, Sep 23, 2009 at 4:11 PM, Janis Johnson <janis...@us.ibm.com> wrote: > On Wed, 2009-09-23 at 10:29 +0200, Richard Guenther wrote: >> On Wed, Sep 23, 2009 at 2:38 AM, Janis Johnson <janis...@us.ibm.com> wrote: >> > I've been implementing ISO/IEC TR 24733, "an extension for the >> > programming language C++ to support decimal floating-point arithmetic", >> > in GCC. It might be ready as an experimental feature for 4.5, but I >> > would particularly like to get in the compiler changes that are needed >> > for it. >> > >> > Most of the support for the TR is in new header files in libstdc++ that >> > depend on compiler support for decimal float scalar types. Most of that >> > compiler functionality was already available in G++ via mode attributes. >> > I've made a couple of small fixes and have a couple more to submit, and >> > when those are in I'll starting running dfp tests for C++ as well as C. >> > The suitable tests have already been moved from gcc.dg to c-c++-common. >> > >> > In order to provide interoperability with C, people on the C++ ABI >> > mailing list suggested that a C++ compiler should recognize the new >> > decimal classes defined in the TR and pass arguments of those types the >> > same as scalar decimal float types for a particular target. I had this >> > working in an ugly way using a langhook, but that broke with LTO. I'm >> > looking for the right places to record that an argument or return value >> > should be passed as if it were a different type, but could use some >> > advice about that. >> >> How do we (do we?) handle std::complex<> there? My first shot would >> be to make sure the aggregate type has the proper mode, but I guess >> most target ABIs would already pass them in registers, no? > > std::complex<> is not interoperable with GCC's complex extension, which > is generally viewed as "unfortunate".
Could you expand on why std::complex<> is not interoperable with GCC's complex extension. The reason is that I would like to know better where the incompatibilities come from -- I've tried to remove any. > > The class types for std::decimal::decimal32 and friends do have the > proper modes. I suppose I could special-case aggregates of those modes > but the plan was to pass these particular classes (and typedefs of > them) the same as scalars, rather than _any_ class with those modes. > I'll bring this up again on the C++ ABI mailing list. I introduced the notion of 'literal types' in C++0x precisely so that compilers can pretend that user-defined types are like builtin types and provide appropriate support. decimal types are literal types. So are std::complex<T> for T = builtin arithmetic types. > > Perhaps most target ABIs pass single-member aggregates using the > mode of the aggregate, but not all. In particular, not the 32-bit > ELF ABI for Power. > > Janis > > > >
