[libre-riscv-dev] Introduction

[Jacob Lifshay]

I implemented the calculator in rust:
https://salsa.debian.org/Kazan-team/softfloat-verify

Supports RPN and multiple calculations per invocation by having one
space-separated sequence of calculations per line. It prints and clears the
stack after each line.
See https://docs.rs/softfloat-sys/0.1.1/softfloat_sys/ for the list of
supported functions and constants.

Since I had to write the softfloat rust bindings and I didn't want to take
much time, I only implemented it for linux x86_64.

I had to work around a bug in softfloat where they used C inline functions
but didn't supply the out-of-line definitions, so it won't build on -O0.
Took lots of time to figure out.

You will want to use softfloat_detectTininess_write_helper and
softfloat_roundingMode_write_helper to set the correct rounding modes and
tininess detection.
You will also want to use softfloat_exceptionFlags_read_helper and
softfloat_exceptionFlags_write_helper to clear and check the exception
flags.

Build instructions:
Install dependencies: sudo apt install cmake build-essential git
Get rust from https://rustup.rs/

git clone https://salsa.debian.org/Kazan-team/softfloat-verify
cd softfloat-verify
cargo build
./softfloat-verify <<<"2 i32_to_f128 f128_sqrt"
observe the f128 sqrt of 2.

Jacob Lifshay

On Sat, Feb 2, 2019 at 11:25 PM Luke Kenneth Casson Leighton <lkcl at lkcl.net>
wrote:

> On Sunday, February 3, 2019, Jacob Lifshay <programmerjake at gmail.com>
> wrote:
>
> > I could write the calculator, shouldn't take very long. It will use
> > integers for i/o, they will be bitcasted to the fp types. This way we
> avoid
> > problems with decimal representations while still being simple enough to
> > implement since not everything can read/write hex floats (like
> > 0x1234.5678P+25).
>
>
> Yeh definitely int representation, fscanf does the job.
>
>
> >
> > Should I use infix notation, lisp-like S expressions, or RPN?
> > I think we should not use infix notation as it's harder to parse and not
> as
> > clear which order operators are being applied.
> >
> > RPN is the easiest to parse.
> > S expressions maintain the familiar operation nesting and is second
> easiest
> > to parse.
>
>
> I hadn't thought about it, basically needs to be dead simple, yet enough to
> represent FMULADD.
>
> even avoid stack, put operator first then operands, because operator can be
> done as a switch statement then straight to read of num of ops, then print
> result. Loop.
>
> fscanf to read line up to \n to get operator.
> switch statement
> fscanf with %x's to read operands.
>
>
>
>
>
> --
> ---
> crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
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