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• Binary

Strval2

Interpret a string as a binary number.

Signature

(strval2 x) → value?

Arguments

x — Guard (stringp x).

Returns

value? — Type (or (natp value?) (not value?)).

For example, (strval2 "1000") is 8. If the string has any characters other than 0 or 1, or is empty, we return nil.

Definitions and Theorems

Function: strval2

(defun strval2 (x)
  (declare (xargs :guard (stringp x)))
  (declare (type string x))
  (declare (xargs :split-types t))
  (let ((acl2::__function__ 'strval2))
    (declare (ignorable acl2::__function__))
    (mbe :logic
         (let ((chars (explode x)))
           (and (consp chars)
                (bin-digit-char-list*p chars)
                (bin-digit-chars-value chars)))
         :exec
         (b* (((the unsigned-byte xl) (length x))
              ((mv (the unsigned-byte val)
                   (the unsigned-byte len))
               (parse-bits-from-string x 0 0 0 xl)))
           (and (not (eql 0 len))
                (eql len xl)
                val)))))

Theorem: return-type-of-strval2

(defthm return-type-of-strval2
  (b* ((value? (strval2 x)))
    (or (natp value?) (not value?)))
  :rule-classes :type-prescription)

Theorem: istreqv-implies-equal-strval2-1

(defthm istreqv-implies-equal-strval2-1
  (implies (istreqv x x-equiv)
           (equal (strval2 x) (strval2 x-equiv)))
  :rule-classes (:congruence))