Re: integer overflow handling for most-negative-fixnum

[Helmut Eller]

> Either the print routines or the reader have a bug.

Read and print work just fine:
(= (read (prin1-to-string most-negative-fixnum))
    most-negative-fixnum) => t

The problem is (format "%x" most-negative-fixnum) => "2000000000000000".
If this should return "-1" that would obviously be an incompatible
change.  And in many cases one really wants to "see" the two complement
representation of negative fixnums.  Just like in gdb: p/x -1 prints
0xffffff.  Interestingly, gdb doesn't seem to have a mode to print hex
numbers with a negative sign; so I guess nobody ever wanted that.

In contrast, it should be unproblematic to add an optional base argument
to number-to-string.  So (number-to-string -1 16) could return
"-2000000000000000" without breaking anything.  Actually, I occasionally
wondered why string-to-number accepts a base argument but
number-to-string doesn't.

(Of course, the question what (format "%x" <bignum>) should do is still
open; the easiest would probably be to signal an error.)

Helmut