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fixnum

fixnum Type

Supertypes:

fixnum, integer, rational, real, number, t

Description:

A fixnum is an integer whose value is between most-negative-fixnum and most-positive-fixnum inclusive. Exactly which integers are fixnums is implementation-defined. The type fixnum is required to be a supertype of (signed-byte 16).

Expanded Reference: fixnum​

Type Checking​

A fixnum is an integer that the implementation can represent efficiently, typically as a machine word. The range is at least from -2^15 to 2^15-1 but is usually much larger.

(typep 0 'fixnum)
=> T
(typep 42 'fixnum)
=> T
(typep -100 'fixnum)
=> T
(typep most-positive-fixnum 'fixnum)
=> T
(typep (1+ most-positive-fixnum) 'fixnum)
=> NIL

Fixnum Range​

The constants most-positive-fixnum and most-negative-fixnum define the implementation-dependent range. On most 64-bit implementations, fixnums cover a very large range.

most-positive-fixnum
=> 4611686018427387903
most-negative-fixnum
=> -4611686018427387904

;; fixnum is equivalent to this integer range
(subtypep 'fixnum `(integer ,most-negative-fixnum ,most-positive-fixnum))
=> T
=> T

Type Hierarchy​

The fixnum type is a subtype of integer and is disjoint from bignum. Together, fixnum and bignum partition the integer type.

(subtypep 'fixnum 'integer)
=> T
=> T
(subtypep 'fixnum 'bignum)
=> NIL
=> T
(type-of 42)
=> (INTEGER 0 4611686018427387903)

Performance Considerations​

Fixnum arithmetic uses efficient machine instructions. Declaring fixnum types can help compilers optimize numeric code.

;; Type declarations for performance
(defun fast-add (a b)
  (declare (type fixnum a b))
  (the fixnum (+ a b)))

(fast-add 10 20)
=> 30