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• Primitive-narrowing-conversions

Char-to-byte

Narrowing conversion from char to byte [JLS14:5.1.3].

Signature

(char-to-byte operand) → result

Arguments

operand — Guard (char-valuep operand).

Returns

result — Type (byte-valuep result).

Definitions and Theorems

Function: char-to-byte

(defun char-to-byte (operand)
  (declare (xargs :guard (char-valuep operand)))
  (b* ((x (char-value->nat operand)))
    (byte-value (logext 8 x))))

Theorem: byte-valuep-of-char-to-byte

(defthm byte-valuep-of-char-to-byte
  (b* ((result (char-to-byte operand)))
    (byte-valuep result))
  :rule-classes :rewrite)

Theorem: char-to-byte-of-char-value-fix-operand

(defthm char-to-byte-of-char-value-fix-operand
  (equal (char-to-byte (char-value-fix operand))
         (char-to-byte operand)))

Theorem: char-to-byte-char-value-equiv-congruence-on-operand

(defthm char-to-byte-char-value-equiv-congruence-on-operand
  (implies (char-value-equiv operand operand-equiv)
           (equal (char-to-byte operand)
                  (char-to-byte operand-equiv)))
  :rule-classes :congruence)