114 lines
3.2 KiB
Java
114 lines
3.2 KiB
Java
/* Copyright (C) 1999 Cygnus Solutions
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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package gnu.gcj.convert;
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/**
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* Convert UTF8 to Unicode.
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* @author Per Bothner <bothner@cygnus.com>
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* @date March 1999.
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*/
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public class Input_UTF8 extends BytesToUnicode
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{
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public String getName() { return "UTF8"; }
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int partial = 0;
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int partial_bytes_expected = 0;
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//int suggogate_second = -1;
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public int read (char[] outbuffer, int outpos, int count)
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{
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int origpos = outpos;
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for (;;)
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{
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if (outpos - origpos >= count)
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break;
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if (inpos >= inlength)
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break;
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int b = inbuffer[inpos++];
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if (b >= 0)
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outbuffer[outpos++] = (char) b;
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else
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{
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if ((b & 0xC0) == 0x80) // Continuation byte
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{
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partial = (partial << 6) | (b & 0x3F);
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--partial_bytes_expected;
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if (partial_bytes_expected == 1)
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{
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if (partial > (0xFFFF>>6))
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{
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// The next continuation byte will cause the result
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// to exceed 0xFFFF, so we must use a surrogate pair.
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// The "Unicode scalar value" (see D28 in section 3.7
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// of the Unicode Standard 2.0) is defined as:
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// value == (hi-0xD800)*0x400+(lo-0xDC00)+0x10000,
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// where (hi, lo) is the Unicode surrogate pair.
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// After reading the first three bytes, we have:
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// partial == (value >> 6).
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// Substituting and simplifying, we get:
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// partial == (hi-0xD800)*0x10+((lo-0xDC00)>>6)+0x400.
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// The definition lo>=0xDC00 && lo<=0xDFFF implies
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// that (lo-0xDC00)>>6 is in the range 0..15.
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// Hence we can infer (partial-0x400)>>4 == (hi-0xDB00)
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// and we can emit the high-surrogate without waiting
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// for the final byte:
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outbuffer[outpos++] = (char) (0xDA00+(partial>>4));
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// Now we want to set it up so that when we read
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// the final byte on the next iteration, we will
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// get the low-surrogate without special handling.
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// I.e. we want:
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// lo == (next_partial << 6) | (next & 0x3F)
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// where next is the next input byte and next_partial
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// is the value of partial at the end of this
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// iteration. This implies: next_partial == lo >> 6.
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// We can simplify the previous:
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// partial == (hi-0xD800)*0x10+((lo-0xDC00)>>6)+0x400,
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// to: partial == (hi-0xD800)*0x10+(lo>>6)+0x90.
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// Inserting the values of hi and next_partial,
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// and simplifying, we get: partial ==
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// ( (partial-0x400)&~0xF) + next_partial + 0x90.
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// Solving for next_partial, we get:
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// next_partial = partial+0x400-0x90-(partial&~0xF):
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// or: next_partial = (partial&0xF) + 0x370. Hence:
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partial = (partial & 0xF) + 0x370;
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}
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}
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else if (partial_bytes_expected == 0)
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{
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outbuffer[outpos++] = (char) partial;
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partial = 0;
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partial_bytes_expected = 0;
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}
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}
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else // prefix byte
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{
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if ((b & 0xE0) == 0xC0)
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{
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partial = b & 0x1F;
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partial_bytes_expected = 1;
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}
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else if ((b & 0xF0) == 0xE0)
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{
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partial = b & 0xF;
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partial_bytes_expected = 2;
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}
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else
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{
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partial = b & 7;
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partial_bytes_expected = 3;
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}
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}
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}
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}
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return outpos - origpos;
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}
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}
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