Can GMP be replaced by trees?

[Joseph S. Myers]

On Tue, 18 May 2004, [ISO-8859-1] Tobias Schlüter wrote:

> With Toon's recent remark about how incorrect rounding due to excess 
> precision in our frontend may corrupt results, and Steve's work which 

Reference?

> revealed several minor mistakes in the GMP code in arith.c, I started 
> wondering if our dependency on GMP can be removed.

If MPFR - part of GMP though not enabled by default - were used, it would
avoid lots of errors (and excess precision) by using already debugged
code.  Cf. < http://gcc.gnu.org/ml/gcc-patches/2003-09/msg00912.html >
listing functions in arith.c duplicating code that already exists in GMP.

By changing the core GCC code (for anything more than +-*/) to use MPFR,
rather than going the other way, support for folding particular functions
is naturally shared by all languages supporting those functions - for
example, you get constant folding for most of the C99 <math.h> and
<complex.h> functions "for free" (as MPFR already implements computing
0.5ulp correctly rounded values for those functions).  (You also fix the
well-known problem that sqrtl can be folded with incorrect rounding on
systems with 106-bit long double.)  Contributions to MPFR to support
functions not already supported help more than just GCC.

-- 
Joseph S. Myers
jsm@polyomino.org.uk