[RFC PATCH v2 2/2] RISC-V: Add support for the Zfa extension

[Kito Cheng]

Wait, I mean the hex floating point format defined in C99/C++17, not
the raw hex value.
so something like 0x1p-16 (0.0000152587890625), 0x1p-2 (0.25) 0x1p+0,
-0x1p+0 could be used for fli.* instruction.

You could use printf with %a to get those values.

https://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html
https://developer.arm.com/documentation/dui0375/latest/Compiler-Coding-Practices/Hexadecimal-floating-point-numbers-in-C99


On Mon, Mar 27, 2023 at 4:39 PM Jan Beulich via Binutils
<binutils@sourceware.org> wrote:
>
> On 27.03.2023 10:01, Christoph Muellner wrote:
> > --- a/opcodes/riscv-opc.c
> > +++ b/opcodes/riscv-opc.c
> > @@ -110,6 +110,16 @@ const char * const riscv_vma[2] =
> >    "mu", "ma"
> >  };
> >
> > +/* The FLI.[HSDQ] value constants.  */
> > +const char * const riscv_fli_value[32] =
> > +{
> > +  "-1.0", "min", "0.0000152587890625", "0.000030517578125",
> > +  "0.00390625", "0.0078125", "0.0625", "0.125",
> > +  "0.25", "0.3125", "0.375", "0.4375", "0.5", "0.625", "0.75", "0.875",
> > +  "1.0", "1.25", "1.5", "1.75", "2.0", "2.5", "3.0", "4.0",
> > +  "8.0", "16.0", "128.0", "256.0", "32768.0", "65536.0",  "inf", "nan",
> > +};
>
> Especially for values like 1.0x2^^-n (entries 2 and onwards) I question
> the spelled out numbers to be the most suitable ones usability wise. At
> least some alternative spelling (e.g. 2.e-16) ought to be recognized as
> well. But since there are meany reasonable spellings (leading 0 omitted
> in 0.<fraction> or trailing zero omitted in <num>.0), I guess I'd prefer
> if values were actually parsed as a floating point number (e.g. via
> ieee_md_atof()), and then matched against values stored in the table.
> One might further consider to also permit the 2nd form accepted
> elsewhere, see read.c:parse_one_float().
>
> Jan