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Std/io

Take-bytes

Read the first n bytes from an open file.

(take-bytes n channel state) is like take for an :byte input channel. That is, it just reads n bytes and returns them as a list, and also returns the updated state.

Definitions and Theorems

Function: take-bytes

(defun take-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)) (mv nil state))
       ((mv a state)
        (read-byte$ channel state))
       ((mv x state)
        (take-bytes (1- n) channel state)))
    (mv (cons a x) state)))

Theorem: state-p1-of-take-bytes

(defthm state-p1-of-take-bytes
  (implies (and (force (state-p1 state))
                (force (symbolp channel))
                (force (open-input-channel-p1 channel
                                              :byte state)))
           (state-p1 (mv-nth 1 (take-bytes n channel state)))))

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

(defthm open-input-channel-p1-of-take-bytes
  (implies (and (force (state-p1 state))
                (force (symbolp channel))
                (force (open-input-channel-p1 channel
                                              :byte state)))
           (open-input-channel-p1
                channel
                :byte (mv-nth 1 (take-bytes n channel state)))))

Theorem: mv-nth0-of-take-bytes

(defthm mv-nth0-of-take-bytes
 (implies (and (force (state-p1 state))
               (force (symbolp channel))
               (force (open-input-channel-p1 channel
                                             :byte state)))
          (equal (mv-nth 0 (take-bytes n channel state))
                 (take n
                       (mv-nth 0 (read-byte$-all channel state))))))

Theorem: mv-nth1-of-take-bytes$

(defthm mv-nth1-of-take-bytes$
  (implies (and (force (state-p1 state))
                (force (symbolp channel))
                (force (open-input-channel-p1 channel
                                              :byte state)))
           (equal (mv-nth 1 (take-bytes n channel state))
                  (nthcdr-bytes n channel state))))