signed-byte

signed-byte Type

Supertypes:

signed-byte, integer, rational, real, number, t

Description:

The atomic type specifier signed-byte denotes the same type as is denoted by the type specifier integer; however, the list forms of these two type specifiers have different semantics.

Compound Type Specifier Kind:

Abbreviating.

Compound Type Specifier Syntax:

(signed-byte [s | *])

Compound Type Specifier Arguments:

s—a positive integer .

Compound Type Specifier Description:

This denotes the set of integers that can be represented in two’s-complement form in a byte of s bits. This is equivalent to (integer −2^s−1 2^s−1 − 1). The type signed-byte or the type (signed-byte *) is the same as the type integer.

Expanded Reference: signed-byte

Type Checking

The type (signed-byte s) denotes the set of integers that can be represented in two's complement form in s bits. It is equivalent to (integer -(2^(s-1)) (2^(s-1) - 1)). The bare type signed-byte without a size is equivalent to integer.

(typep 0 '(signed-byte 8))
=> T
(typep 127 '(signed-byte 8))
=> T
(typep -128 '(signed-byte 8))
=> T
(typep 128 '(signed-byte 8))
=> NIL
(typep -129 '(signed-byte 8))
=> NIL

Different Sizes

The size parameter specifies the total number of bits including the sign bit.

;; (signed-byte 8) → range -128 to 127
(typep 127 '(signed-byte 8))
=> T
(typep -128 '(signed-byte 8))
=> T

;; (signed-byte 16) → range -32768 to 32767
(typep 32767 '(signed-byte 16))
=> T
(typep 32768 '(signed-byte 16))
=> NIL

;; (signed-byte 32) → range -2147483648 to 2147483647
(typep 2147483647 '(signed-byte 32))
=> T

Relationship to integer

The bare signed-byte type specifier (without a size) is equivalent to integer, encompassing all integers.

(subtypep 'signed-byte 'integer)
=> T
=> T
(subtypep 'integer 'signed-byte)
=> T
=> T
(subtypep '(signed-byte 8) '(signed-byte 16))
=> T
=> T
(subtypep '(signed-byte 16) '(signed-byte 8))
=> NIL
=> T

Use in Array Element Types

The signed-byte type is commonly used to declare compact array element types for memory-efficient storage.

(make-array 4 :element-type '(signed-byte 8)
              :initial-contents '(-1 0 1 127))
=> #(-1 0 1 127)

(array-element-type
  (make-array 4 :element-type '(signed-byte 8)))
=> (SIGNED-BYTE 8)