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; Standard IO Library
; take-bytes.lisp -- originally part of the Unicode library
; Copyright (C) 2005-2013 Kookamara LLC
;
; Contact:
;
; Kookamara LLC
; 11410 Windermere Meadows
; Austin, TX 78759, USA
; http://www.kookamara.com/
;
; License: (An MIT/X11-style license)
;
; Permission is hereby granted, free of charge, to any person obtaining a
; copy of this software and associated documentation files (the "Software"),
; to deal in the Software without restriction, including without limitation
; the rights to use, copy, modify, merge, publish, distribute, sublicense,
; and/or sell copies of the Software, and to permit persons to whom the
; Software is furnished to do so, subject to the following conditions:
;
; The above copyright notice and this permission notice shall be included in
; all copies or substantial portions of the Software.
;
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
; DEALINGS IN THE SOFTWARE.
;
; Original author: Jared Davis <jared@kookamara.com>
(in-package "ACL2")
(include-book "read-file-bytes")
(include-book "nthcdr-bytes")
(local (include-book "base"))
(local (include-book "arithmetic/top" :dir :system))
(local (include-book "tools/mv-nth" :dir :system))
(local (include-book "std/lists/take" :dir :system))
(set-state-ok t)
(defsection take-bytes
:parents (std/io)
:short "Read the first @('n') bytes from an open file."
:long "<p>@(call take-bytes) is like @(see 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.</p>"
(defund 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)))
(local (in-theory (enable take-bytes nthcdr-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)))))
(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)))))
(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$-all channel state)))))
:hints(("Goal"
:in-theory (enable take read-byte$-all repeat)
:induct (take-bytes n channel state))))
(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)))))
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