Re: 1 - 1, 1 -1, 1-1, 1 - -1 and -2147483648

Edsko de Vries <devriese@cs.tcd.ie> wrote:
>The problem is, of course, overflow: -2147483648 is a valid negative
>number (assuming 32-bit numbers), but the integer 2147483648 is _not_ a
>valid positive number... Is there a good solution...?


The hack that has been used for this in the past is to compute and store a
number as the negative of its actual value (temporarily, until you know
whether there's a unary minus in front).


If that's too distasteful, you really have to find an extra bit somewhere:


+ Store the constant as an unsigned number (32-bit unsigned goes up to
    4_294_967_295 without overflow, so 2_147_483_648 is no problem),
    until you know the sign.


+ Use a larger signed type, if you have one.


+ Use a bignum (unlimited-length integer) library.


+ Store the number as a string, unconverted, until you know its sign.


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