musl - Do you recommend using fmt

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Message-ID: <CA+fZqCXm-nAzf+j88EqTx_G6jCR-VMN5TyDmgvL-o9yNW+6BUw@mail.gmail.com>
Date: Thu, 18 Aug 2022 17:51:26 +0200
From: ardi <ardillasdelmonte@...il.com>
To: musl@...ts.openwall.com
Subject: Do you recommend using fmt_fp() and

Hi,

I'm looking for a small and robust dtoa-like implementation for quad
floats (IEEE binary128). The need is because I'm using John Hauser's
SoftFloat for IEEE binary128 computing, but I have no easy means for
converting such floats from/to strings (I can use the host
printf/strtold for 80bit extended long doubles, but I'm missing some
significant digits by doing that, and besides, if I ever build in a
host that considers long doubles as regular doubles, I'd lose even
more digits).

I've been considering gdtoa for some days, taking into account its
pros and cons, but I don't like its code size, its dependency on the
FPU flavour behaviour, and that it requires mutexes if it's used in
parallel.

So, I was looking at how musl does this. It appears to be in the
fmt_fp() function in vfprintf.c and in floatscan.c

It looks like I can modify these functions and force them to use the
binary128 type as provided by SoftFloat, instead of using long double.

But it can require quite a bit of surgery, so, before I get my hands
busy in it, I have to ask the question: Would you use this
implementation for my needs if you were me?

Did you adapt fmt_fp() and floatscan from older code? Was that code
ready for 128bit floats?

Or maybe you can recommend another dtoa-like code for 128bit floats?

Thanks a lot,

César

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