• Top
  • Documentation
  • Books
  • Boolean-reasoning
  • Projects
  • Debugging
  • Std
  • Proof-automation
  • Macro-libraries
  • ACL2
  • Interfacing-tools
    • Io
      • Fmt
      • Msg
      • Cw
      • Set-evisc-tuple
      • Set-iprint
      • Print-control
      • Read-file-into-string
      • Std/io
        • Open-channel-lemmas
        • Std/io/read-char$
        • Std/io/read-object
        • Std/io/open-output-channel
        • Unsound-read
        • Read-string
        • Read-bytes$
        • File-measure
        • Read-bytes$-n
        • Std/io/read-byte$
        • Std/io/open-input-channel
        • Read-file-lines-no-newlines
        • Print-compressed
        • Nthcdr-bytes
        • Read-file-lines
        • Std/io/close-output-channel
        • Read-file-characters
        • Read-file-bytes
        • Print-legibly
        • Std/io/close-input-channel
        • Read-file-objects
        • Logical-story-of-io
        • Take-bytes
        • Std/io/peek-char$
        • Read-file-characters-rev
        • Read-file-as-string
        • Std/io/write-byte$
        • Std/io/set-serialize-character
        • Std/io/print-object$
        • Std/io/princ$
        • Std/io/read-file-into-string
        • *file-types*
      • Msgp
      • Printing-to-strings
      • Evisc-tuple
      • Output-controls
      • Observation
      • *standard-co*
      • Ppr-special-syms
      • Standard-oi
      • Standard-co
      • Without-evisc
      • Serialize
      • Output-to-file
      • Fmt-to-comment-window
      • Princ$
      • Character-encoding
      • Open-output-channel!
      • Cw-print-base-radix
      • Set-print-case
      • Set-print-base
      • Print-object$
      • Extend-pathname
      • Print-object$+
      • Fmx-cw
      • Set-print-radix
      • Set-fmt-hard-right-margin
      • File-write-date$
      • Proofs-co
      • Set-print-base-radix
      • Print-base-p
      • *standard-oi*
      • Wof
      • File-length$
      • Fms!-lst
      • Delete-file$
      • *standard-ci*
      • Write-list
      • Trace-co
      • Fmt!
      • Fms
      • Cw!
      • Fmt-to-comment-window!
      • Fms!
      • Eviscerate-hide-terms
      • Fmt1!
      • Fmt-to-comment-window!+
      • Read-file-into-byte-array-stobj
      • Fmt1
      • Fmt-to-comment-window+
      • Cw-print-base-radix!
      • Read-file-into-character-array-stobj
      • Fmx
      • Cw!+
      • Read-objects-from-book
      • Newline
      • Cw+
      • Probe-file
      • Write-objects-to-file!
      • Write-objects-to-file
      • Read-objects-from-file
      • Read-object-from-file
      • Read-file-into-byte-list
      • Set-fmt-soft-right-margin
      • Read-file-into-character-list
      • Io-utilities
    • Defttag
    • Sys-call
    • Save-exec
    • Quicklisp
    • Std/io
      • Open-channel-lemmas
      • Std/io/read-char$
      • Std/io/read-object
      • Std/io/open-output-channel
      • Unsound-read
      • Read-string
      • Read-bytes$
      • File-measure
      • Read-bytes$-n
      • Std/io/read-byte$
      • Std/io/open-input-channel
      • Read-file-lines-no-newlines
      • Print-compressed
      • Nthcdr-bytes
      • Read-file-lines
      • Std/io/close-output-channel
      • Read-file-characters
      • Read-file-bytes
      • Print-legibly
      • Std/io/close-input-channel
      • Read-file-objects
      • Logical-story-of-io
      • Take-bytes
      • Std/io/peek-char$
      • Read-file-characters-rev
      • Read-file-as-string
      • Std/io/write-byte$
      • Std/io/set-serialize-character
      • Std/io/print-object$
      • Std/io/princ$
      • Std/io/read-file-into-string
      • *file-types*
    • Oslib
    • Bridge
    • Clex
    • Tshell
    • Unsound-eval
    • Hacker
    • ACL2s-interface
    • Startup-banner
    • Command-line
  • Hardware-verification
  • Software-verification
  • Math
  • Testing-utilities

• Std/io

Nthcdr-bytes

Skip past some number of bytes in an open file.

(nthcdr-bytes n channel state) is like nthcdr for an :byte input channel. That is, it just reads n bytes and ignores them, returning the updated state.

This is notably useful as a way to express the post-state after take-bytes.

Definitions and Theorems

Function: nthcdr-bytes

(defun nthcdr-bytes (n channel state)
  (declare (xargs :guard (and (natp n)
                              (state-p state)
                              (symbolp channel)
                              (open-input-channel-p channel
                                                    :byte state))))
  (b* (((when (zp n)) state)
       ((mv ?byte state)
        (read-byte$ channel state)))
    (nthcdr-bytes (- n 1) channel state)))

Theorem: state-p1-of-nthcdr-bytes

(defthm state-p1-of-nthcdr-bytes
  (implies (and (force (state-p1 state))
                (force (symbolp channel))
                (force (open-input-channel-p1 channel
                                              :byte state)))
           (state-p1 (nthcdr-bytes n channel state))))

Theorem: open-input-channel-p1-of-nthcdr-bytes

(defthm open-input-channel-p1-of-nthcdr-bytes
 (implies
      (and (force (state-p1 state))
           (force (symbolp channel))
           (force (open-input-channel-p1 channel
                                         :byte state)))
      (open-input-channel-p1 channel
                             :byte (nthcdr-bytes n channel state))))

Theorem: read-byte$-all-of-nthcdr-bytes

(defthm read-byte$-all-of-nthcdr-bytes
 (implies
  (and (force (state-p1 state))
       (force (symbolp channel))
       (force (open-input-channel-p1 channel
                                     :byte state)))
  (equal
    (mv-nth 0
            (read-byte$-all channel (nthcdr-bytes n channel state)))
    (nthcdr n
            (mv-nth 0 (read-byte$-all channel state))))))

Theorem: nthcdr-bytes-1

(defthm nthcdr-bytes-1
  (equal (nthcdr-bytes 1 channel state)
         (mv-nth 1 (read-byte$ channel state))))

Theorem: nthcdr-bytes-2

(defthm nthcdr-bytes-2
  (equal
       (nthcdr-bytes 2 channel state)
       (mv-nth 1
               (read-byte$ channel
                           (mv-nth 1 (read-byte$ channel state))))))

Theorem: nthcdr-bytes-3

(defthm nthcdr-bytes-3
 (equal
  (nthcdr-bytes 3 channel state)
  (mv-nth
   1
   (read-byte$
     channel
     (mv-nth 1
             (read-byte$ channel
                         (mv-nth 1 (read-byte$ channel state))))))))

Theorem: nthcdr-bytes-4

(defthm nthcdr-bytes-4
 (equal
  (nthcdr-bytes 4 channel state)
  (mv-nth
   1
   (read-byte$
    channel
    (mv-nth
     1
     (read-byte$
      channel
      (mv-nth
           1
           (read-byte$ channel
                       (mv-nth 1 (read-byte$ channel state))))))))))

Theorem: nthcdr-bytes-measure-weak

(defthm nthcdr-bytes-measure-weak
  (implies (and (force (state-p1 state))
                (force (open-input-channel-p1 channel
                                              :byte state))
                (force (symbolp channel)))
           (<= (file-measure channel (nthcdr-bytes n channel state))
               (file-measure channel state)))
  :rule-classes (:rewrite :linear))

Theorem: nthcdr-bytes-measure-strong

(defthm nthcdr-bytes-measure-strong
  (implies (and (mv-nth 0 (read-byte$ channel state))
                (not (zp n))
                (force (state-p1 state))
                (force (open-input-channel-p1 channel
                                              :byte state))
                (force (symbolp channel)))
           (< (file-measure channel (nthcdr-bytes n channel state))
              (file-measure channel state)))
  :rule-classes (:rewrite :linear))