* Stefan Monnier [2009-12-03 21:52+0100] writes:

>> (setq x (string-to-number (number-to-string most-positive-fixnum)))
>> (= most-positive-fixnum x) => nil
>    
>> x is 2305843009213693440 but it should be most-positive-fixnum
>> which is 2305843009213693951.
>
>> The test
>> (= most-positive-fixnum 
>>    (string-to-number (number-to-string most-positive-fixnum)))
>> seems to work as expected on 32-bit machines but not so on 64 bit.
>
> Indeed, it passes through a floating point conversion, so there's only
> abour 52 bit of precesion.

Here is a patch for string-to-number to use the full fixnum range: