Re: When does GCC need to use the functions decode_ieee_single()/decode_ieee_double() ?

[pengsheng.chen@gmail.com]

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Dear Jakub,

Thank you for your reply promptly. I have tried many test cases, but I
still cannot trigger the functions: decode_ieee_xxx(). Can you give me some
cases for studying?

Thank you.

Peng-Sheng


On Mon, Sep 19, 2022 at 9:36 PM Jakub Jelinek <jakub@redhat.com> wrote:

> On Mon, Sep 19, 2022 at 09:22:55PM +0800, pengsheng.chen--- via Gcc wrote:
> > The functions encode_ieee_single()/encode_ieee_double() encode the GCC
> > internal representation (i.e., REAL_VALUE_TYPE) to the corresponding IEEE
> > single precision/double precision formats. The constant values in a
> program
> > (i.e., float a = 3.14;) will be parsed and then transferred to GCC
> > REAL_VALUE_TYPE. Later, the REAL_VALUE_TYPE is encoded to IEEE
> > single/double formats. However, I do not know why we need
> > decode_ieee_single()/decode_ieee_double()? Which situations or C code
> > fragments are these decode_ieee_xxx functions used in?
>
> Anywhere where real_from_target is called.
> That is usually when you say have a union of one of the floating point
> types and corresponding integral type, you store the integer into the
> union and read back the floating point, so e.g. when folding
> in the IL VIEW_CONVERT_EXPR <float> (some_int_value) etc.
> Or e.g. when folding RTL NOT of a constant, that inverts all the bits,
> so you need real_to_target, invert the bits and real_from_target back.
>
>         Jakub
>
>