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2.4.1 Integer Type

Under the hood, there are two kinds of integers—small integers, called fixnums, and large integers, called bignums.

The range of values for a fixnum depends on the machine. The minimum range is -536,870,912 to 536,870,911 (30 bits; i.e., -2**29 to 2**29 - 1) but many machines provide a wider range.

Bignums can have arbitrary precision. Operations that overflow a fixnum will return a bignum instead.

All numbers can be compared with eql or =; fixnums can also be compared with eq. To test whether an integer is a fixnum or a bignum, you can compare it to most-negative-fixnum and most-positive-fixnum, or you can use the convenience predicates fixnump and bignump on any object.

The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading ‘+’ or a final ‘.’.

-1               ; The integer -1.
1                ; The integer 1.
1.               ; Also the integer 1.
+1               ; Also the integer 1.

See Numbers, for more information.