On 7/21/2012 15:06, Sisyphus wrote:
> Hi,
>
> I'm using a mingw64 port of gcc-4.7.0 on Windows Vista64:
>
> #############################
> C:\_32\C>x86_64-w64-mingw32-gcc -v
> Using built-in specs.
> COLLECT_GCC=x86_64-w64-mingw32-gcc
> COLLECT_LTO_WRAPPER=c:/_64/alt/bin/../libexec/gcc/x86_64-w64-mingw32/4.7.0/lto-wrapper.exe
> Target: x86_64-w64-mingw32
> Configured with:
> ../../../build/gcc/src/configure --target=x86_64-w64-mingw32
> --prefix=/c/bb/vista64-mingw32/mingw-x86-x86_64/build/build/root
> --with-sysroot=/c/bb/vista64-mingw32/mingw-x86-x86_64/build/build/root
> --enable-languages=all,obj-c++
> --enable-fully-dynamic-string --disable-multilib
> Thread model: win32
> gcc version 4.7.0 20110410 (experimental) (GCC)
> ############################
>
> I'm just starting to play with the _Decimal64 type.
> First thing I'm wondering is how we reliably print out the _Decimal64 values
> in our programs. Is there a formatter we can use with printf() ?
>
> For the moment, I've simply been casting the _Decimal64 variable to a double
> and formatting with %f:
> printf("%f\n", (double)decimal64);
>
> That's good enough to show me that I'm getting sane values - though I think
> I ought to find out how to do it correctly.
>
> I did, however, come across something that appears to me to be *not* so
> sane:
>
> ############################
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void) {
> _Decimal64 inf_d64, nan_d64;
> double inf_d, nan_d;
>
> inf_d64 = 1.0DD/0.0DD;
> inf_d = 1.0/0.0;
>
> nan_d64 = inf_d64/inf_d64;
> nan_d = inf_d/inf_d;
>
> printf("%f %f\n", (double)nan_d64, nan_d);
>
> nan_d64 = -nan_d64;
> nan_d = -nan_d;
>
> printf("%f %f\n", (double)nan_d64, nan_d);
>
> return 0;
> }
>
> /**********************
> Outputs:
> 1.#QNAN0 -1.#IND00
> -1.#IND00 1.#QNAN0
>
> Expected:
> -1.#IND00 -1.#IND00
> 1.#QNAN0 1.#QNAN0
> ***********************/
> ############################
>
> Whereas the "positive" nan is usually represented as -1.#IND00 and the
> "negative" nan as 1.#QNAN0, the _Decimal64 nans are (it seems) being
> represented the other way about.
>
> Is this just a consequence of my improper way of printing those _Decimal64
> values ?
> What ought we see when we print a _Decimal64 nan on Windows?
>
> Cheers,
> Rob
> I'm surprised it works at all, the decimal float math support routines are missing from mingw-w64 crt. Other than that, I can't really comment on the correctness. Perhaps you can look at <http://h21007.www2.hp.com/portal/site/dspp/menuitem.863c3e4cbcdc3f3515b49c108973a801?ciid=8cf166fedd1aa110VgnVCM100000a360ea10RCRD> for reference.
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