• Top
  • Documentation
  • Books
  • Boolean-reasoning
  • Projects
  • Debugging
  • Community
  • Std
    • Std/lists
    • Omaps
    • Std/alists
    • Obags
    • Std/util
    • Std/strings
      • Pretty-printing
      • Printtree
      • Base64
      • Charset-p
      • Strtok!
      • Cases
      • Concatenation
      • Character-kinds
      • Html-encoding
      • Substrings
      • Strtok
      • Equivalences
      • Url-encoding
      • Lines
      • Explode-implode-equalities
      • Ordering
      • Numbers
        • Decimal
          • Parse-nat-from-string
          • Parse-nat-from-charlist
          • Nat-to-dec-chars
          • Dec-digit-char-p
          • Dec-digit-chars-value
          • Dec-digit-char-listp
          • Take-leading-dec-digit-chars
          • Dec-digit-char-value
          • Dec-digit-char-list*p
          • Nat-to-dec-string-width
          • Nat-to-dec-string
          • Dec-digit-string-p
          • Strval
          • Skip-leading-digits
          • Nat-to-dec-string-size
          • Int-to-dec-string-width
          • Int-to-dec-string
          • Nonzero-dec-digit-char-p
          • Nat-to-dec-string-list
          • Int-to-dec-string-list
          • Revappend-nat-to-dec-chars
        • Hex
        • Octal
        • Binary
      • Pad-trim
      • Coercion
      • Std/strings/digit-to-char
      • Substitution
      • Symbols
    • Std/osets
    • Std/io
    • Std/basic
    • Std/system
    • Std/typed-lists
    • Std/bitsets
    • Std/testing
    • Std/typed-alists
    • Std/stobjs
  • Proof-automation
  • Macro-libraries
  • ACL2
  • Interfacing-tools
  • Hardware-verification
  • Software-verification
  • Math
  • Testing-utilities

• Decimal

Parse-nat-from-charlist

Parse a natural number from the beginning of a character list.

Signature

(parse-nat-from-charlist x val len) → (mv val len rest)

Arguments

x — Characters to read from.
    Guard (character-listp x).

val — Accumulator for the value of the digits we have read so far; typically 0 to start with.
    Guard (natp val).

len — Accumulator for the number of digits we have read; typically 0 to start with.
    Guard (natp len).

Returns

val — Value of the initial digits as a natural number.

len — Number of initial digits we read.

rest — The rest of x, past the leading digits.

This function is somewhat complicated. See also (dec-digit-chars-value x), which is a simpler way to interpret strings where all of the characters are digits.

Definitions and Theorems

Function: parse-nat-from-charlist

(defun parse-nat-from-charlist (x val len)
 (declare (xargs :guard (and (character-listp x)
                             (natp val)
                             (natp len))))
 (declare (type unsigned-byte val len))
 (declare (xargs :split-types t))
 (let ((acl2::__function__ 'parse-nat-from-charlist))
  (declare (ignorable acl2::__function__))
  (mbe
   :logic
   (cond
       ((atom x)
        (mv (nfix val) (nfix len) nil))
       ((dec-digit-char-p (car x))
        (let ((dec-digit-char-value (dec-digit-char-value (car x))))
          (parse-nat-from-charlist
               (cdr x)
               (+ dec-digit-char-value (* 10 (nfix val)))
               (+ 1 (nfix len)))))
       (t (mv (nfix val) (nfix len) x)))
   :exec
   (b* (((when (atom x)) (mv val len nil))
        ((the (unsigned-byte 8) code)
         (char-code (the character (car x))))
        ((unless (and (<= (the (unsigned-byte 8) code)
                          (the (unsigned-byte 8) 57))
                      (<= (the (unsigned-byte 8) 48)
                          (the (unsigned-byte 8) code))))
         (mv val len x))
        ((the (unsigned-byte 8)
              dec-digit-char-value)
         (the (unsigned-byte 8)
              (- (the (unsigned-byte 8) code)
                 (the (unsigned-byte 8) 48)))))
     (parse-nat-from-charlist
          (cdr x)
          (the unsigned-byte
               (+ (the (unsigned-byte 8)
                       dec-digit-char-value)
                  (the unsigned-byte (* 10 val))))
          (the unsigned-byte
               (+ 1 (the integer len))))))))

Theorem: val-of-parse-nat-from-charlist

(defthm val-of-parse-nat-from-charlist
  (equal (mv-nth 0 (parse-nat-from-charlist x val len))
         (+ (dec-digit-chars-value (take-leading-dec-digit-chars x))
            (* (nfix val)
               (expt 10
                     (len (take-leading-dec-digit-chars x)))))))

Theorem: len-of-parse-nat-from-charlist

(defthm len-of-parse-nat-from-charlist
  (equal (mv-nth 1 (parse-nat-from-charlist x val len))
         (+ (nfix len)
            (len (take-leading-dec-digit-chars x)))))

Theorem: rest-of-parse-nat-from-charlist

(defthm rest-of-parse-nat-from-charlist
  (equal (mv-nth 2 (parse-nat-from-charlist x val len))
         (skip-leading-digits x)))