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Re: real.c implementation
On Sun, Oct 20, 2002 at 10:00:41PM -0500, Brad Lucier wrote:
> It may give more confidence if you set up an artificial arithmetic
> that has 158-bit accuracy to be tested by paranoia.
Working on it. There are a couple of failures.
> I don't know the answers to these questions. Steele and White, Clinger,
> and David Gay (his code is at netlib.org) worked out provably correct methods
> to do exact binary<->decimal conversion. All of them rely on extra-precision
> integer arithmetic for some cases. I don't know if Moshier's code has this
> property, and I don't know if it benefits from extra intermediate precision.
Neither the current code nor the previous use arbitrary precision integer
arithmetic. Both versions, as far as I can tell, rely on being about to
compute 10**N with lg(N) multiplications with "enough" accuracy.
> Is exact conversion a goal for gcc?
I'd say so.
I'm actually *less* concerned about binary->decimal, since for almost
all targets this is only used for debugging dumps -- fp constants are
emitted in the assembly as integer data. There are a few hold-outs
though, so I don't want to be gratuitously wrong either.
r~