adam@1592: (* Copyright (c) 2011, Adam Chlipala
adam@1592:  * All rights reserved.
adam@1592:  *
adam@1592:  * Redistribution and use in source and binary forms, with or without
adam@1592:  * modification, are permitted provided that the following conditions are met:
adam@1592:  *
adam@1592:  * - Redistributions of source code must retain the above copyright notice,
adam@1592:  *   this list of conditions and the following disclaimer.
adam@1592:  * - Redistributions in binary form must reproduce the above copyright notice,
adam@1592:  *   this list of conditions and the following disclaimer in the documentation
adam@1592:  *   and/or other materials provided with the distribution.
adam@1592:  * - The names of contributors may not be used to endorse or promote products
adam@1592:  *   derived from this software without specific prior written permission.
adam@1592:  *
adam@1592:  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
adam@1592:  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
adam@1592:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
adam@1592:  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
adam@1592:  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
adam@1592:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
adam@1592:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
adam@1592:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
adam@1592:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
adam@1592:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
adam@1592:  * POSSIBILITY OF SUCH DAMAGE.
adam@1592:  *)
adam@1592: 
adam@1592: (* UTF-8 conversion *)
adam@1592: 
adam@1592: structure Utf8 :> UTF8 = struct
adam@1592: 
adam@1592: fun byte n = str (chr (Word.toInt n))
adam@1592: 
adam@1592: fun encode n =
adam@1592:     if n <= 0 then
adam@1592:         raise Fail "Invalid character to UTF-8-encode"
adam@1592:     else if n <= 0x7F then
adam@1592:         str (chr n)
adam@1592:     else if n <= 0x7FF then
adam@1592:         let
adam@1592:             val w = Word.fromInt n
adam@1592:             val b1 = Word.orb (Word.fromInt (128 + 64), Word.>> (w, Word.fromInt 6))
adam@1592:             val b2 = Word.orb (Word.fromInt 128, Word.andb (w, Word.fromInt 63))
adam@1592:         in
adam@1592:             byte b1 ^ byte b2
adam@1592:         end
adam@1592:     else if n <= 0xFFFF then
adam@1592:         let
adam@1592:             val w = Word.fromInt n
adam@1592:             val b1 = Word.orb (Word.fromInt (128 + 64 + 32), Word.>> (w, Word.fromInt 12))
adam@1592:             val b2 = Word.orb (Word.fromInt 128, Word.andb (Word.>> (w, Word.fromInt 6), Word.fromInt 63))
adam@1592:             val b3 = Word.orb (Word.fromInt 128, Word.andb (w, Word.fromInt 63))
adam@1592:         in
adam@1592:             byte b1 ^ byte b2 ^ byte b3
adam@1592:         end
adam@1592:     else
adam@1592:         raise Fail "Exceeded supported range for UTF-8 characters"
adam@1592: 
adam@1592: end