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Bytep

Recognize unsigned 8-bit bytes.

Signature
(bytep x) → yes/no
Returns: yes/no — Type (booleanp yes/no).

ACL2 has a flexible notion of `byte', which may be signed or unsigned, and consist of (almost) any number of bits: see unsigned-byte-p and signed-byte-p. But very often the unqualified term `byte' refers to a sequence of exactly 8 bits, represented by natural numbers below 256: this predicate caters to this common terminology.

Definitions and Theorems

Function: bytep

(defun bytep (x)
  (declare (xargs :guard t))
  (mbe :logic (unsigned-byte-p 8 x)
       :exec (and (integerp x) (<= 0 x) (< x 256))))

Theorem: booleanp-of-bytep

(defthm booleanp-of-bytep
  (b* ((yes/no (bytep x)))
    (booleanp yes/no))
  :rule-classes :rewrite)

Theorem: bytep-compound-recognizer

(defthm bytep-compound-recognizer
  (implies (bytep x)
           (and (integerp x) (<= 0 x)))
  :rule-classes :compound-recognizer)

Subtopics

Byte: A fixtype of (unsigned 8-bit) bytes.
Bytes-as-digits-in-base-256: Specialized versions of the operations to convert between natural numbers and digits that use bytes as digits, in base 256.
Bytep-additional-theorems: Additional theorems about byte.