Custom error handling function

[Jeroen Demeyer]

Hello,

there are a few places in GMP where it catches some invalid operation 
and it calls abort() or __gmp_invalid_operation(), which in turn raises 
SIGFPE.

For interactive programs using GMP, it would be useful to have a custom 
error handler instead. So, analogous to mp_set_memory_functions(), one 
could have mp_set_error_functions().

My more concrete proposal would be to have 2 error functions, one to 
replace abort() and one to replace __gmp_invalid_operation(), each with 
a "const char* msg" argument containing an error message.

In mpz/init2.c for example, the lines

       fprintf (stderr, "gmp: overflow in mpz type\n");
       abort ();

would be replaced by something like

       GMP_ERROR("gmp: overflow in mpz type")

This should be easy to implement and it can be totally backwards 
compatible. Several other math libraries like PARI/GP, NTL and GLPK 
allow an analogous error handler. What do you think?


Cheers,
Jeroen.