utf8.cpp

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/*
 * Copyright (C) 2007 Apple Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#include "UTF8.h"

namespace WTF {
namespace Unicode {

inline int inlineUTF8SequenceLengthNonASCII(char b0)
{
    if ((b0 & 0xC0) != 0xC0)
        return 0;
    if ((b0 & 0xE0) == 0xC0)
        return 2;
    if ((b0 & 0xF0) == 0xE0)
        return 3;
    if ((b0 & 0xF8) == 0xF0)
        return 4;
    return 0;
}

inline int inlineUTF8SequenceLength(char b0)
{
    return (b0 & 0x80) == 0 ? 1 : inlineUTF8SequenceLengthNonASCII(b0);
}

int UTF8SequenceLength(char b0)
{
    return (b0 & 0x80) == 0 ? 1 : inlineUTF8SequenceLengthNonASCII(b0);
}

int decodeUTF8Sequence(const char* sequence)
{
    // Handle 0-byte sequences (never valid).
    const unsigned char b0 = sequence[0];
    const int length = inlineUTF8SequenceLength(b0);
    if (length == 0)
        return -1;

    // Handle 1-byte sequences (plain ASCII).
    const unsigned char b1 = sequence[1];
    if (length == 1) {
        if (b1)
            return -1;
        return b0;
    }

    // Handle 2-byte sequences.
    if ((b1 & 0xC0) != 0x80)
        return -1;
    const unsigned char b2 = sequence[2];
    if (length == 2) {
        if (b2)
            return -1;
        const int c = ((b0 & 0x1F) << 6) | (b1 & 0x3F);
        if (c < 0x80)
            return -1;
        return c;
    }

    // Handle 3-byte sequences.
    if ((b2 & 0xC0) != 0x80)
        return -1;
    const unsigned char b3 = sequence[3];
    if (length == 3) {
        if (b3)
            return -1;
        const int c = ((b0 & 0xF) << 12) | ((b1 & 0x3F) << 6) | (b2 & 0x3F);
        if (c < 0x800)
            return -1;
        // UTF-16 surrogates should never appear in UTF-8 data.
        if (c >= 0xD800 && c <= 0xDFFF)
            return -1;
        return c;
    }

    // Handle 4-byte sequences.
    if ((b3 & 0xC0) != 0x80)
        return -1;
    const unsigned char b4 = sequence[4];
    if (length == 4) {
        if (b4)
            return -1;
        const int c = ((b0 & 0x7) << 18) | ((b1 & 0x3F) << 12) | ((b2 & 0x3F) << 6) | (b3 & 0x3F);
        if (c < 0x10000 || c > 0x10FFFF)
            return -1;
        return c;
    }

    return -1;
}

// Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
// into the first byte, depending on how many bytes follow.  There are
// as many entries in this table as there are UTF-8 sequence types.
// (I.e., one byte sequence, two byte... etc.). Remember that sequencs
// for *legal* UTF-8 will be 4 or fewer bytes total.
static const unsigned char firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

ConversionResult convertUTF16ToUTF8(
    const UChar** sourceStart, const UChar* sourceEnd, 
    char** targetStart, char* targetEnd, bool strict)
{
    ConversionResult result = conversionOK;
    const UChar* source = *sourceStart;
    char* target = *targetStart;
    while (source < sourceEnd) {
        UChar32 ch;
        unsigned short bytesToWrite = 0;
        const UChar32 byteMask = 0xBF;
        const UChar32 byteMark = 0x80; 
        const UChar* oldSource = source; // In case we have to back up because of target overflow.
        ch = static_cast<unsigned short>(*source++);
        // If we have a surrogate pair, convert to UChar32 first.
        if (ch >= 0xD800 && ch <= 0xDBFF) {
            // If the 16 bits following the high surrogate are in the source buffer...
            if (source < sourceEnd) {
                UChar32 ch2 = static_cast<unsigned short>(*source);
                // If it's a low surrogate, convert to UChar32.
                if (ch2 >= 0xDC00 && ch2 <= 0xDFFF) {
                    ch = ((ch - 0xD800) << 10) + (ch2 - 0xDC00) + 0x0010000;
                    ++source;
                } else if (strict) { // it's an unpaired high surrogate
                    --source; // return to the illegal value itself
                    result = sourceIllegal;
                    break;
                }
            } else { // We don't have the 16 bits following the high surrogate.
                --source; // return to the high surrogate
                result = sourceExhausted;
                break;
            }
        } else if (strict) {
            // UTF-16 surrogate values are illegal in UTF-32
            if (ch >= 0xDC00 && ch <= 0xDFFF) {
                --source; // return to the illegal value itself
                result = sourceIllegal;
                break;
            }
        }
        // Figure out how many bytes the result will require
        if (ch < (UChar32)0x80) {
            bytesToWrite = 1;
        } else if (ch < (UChar32)0x800) {
            bytesToWrite = 2;
        } else if (ch < (UChar32)0x10000) {
            bytesToWrite = 3;
        } else if (ch < (UChar32)0x110000) {
            bytesToWrite = 4;
        } else {
            bytesToWrite = 3;
            ch = 0xFFFD;
        }

        target += bytesToWrite;
        if (target > targetEnd) {
            source = oldSource; // Back up source pointer!
            target -= bytesToWrite;
            result = targetExhausted;
            break;
        }
        switch (bytesToWrite) { // note: everything falls through.
            case 4: *--target = (char)((ch | byteMark) & byteMask); ch >>= 6;
            case 3: *--target = (char)((ch | byteMark) & byteMask); ch >>= 6;
            case 2: *--target = (char)((ch | byteMark) & byteMask); ch >>= 6;
            case 1: *--target =  (char)(ch | firstByteMark[bytesToWrite]);
        }
        target += bytesToWrite;
    }
    *sourceStart = source;
    *targetStart = target;
    return result;
}

// This must be called with the length pre-determined by the first byte.
// If presented with a length > 4, this returns false.  The Unicode
// definition of UTF-8 goes up to 4-byte sequences.
static bool isLegalUTF8(const unsigned char* source, int length)
{
    unsigned char a;
    const unsigned char* srcptr = source + length;
    switch (length) {
        default: return false;
        // Everything else falls through when "true"...
        case 4: if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
        case 3: if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
        case 2: if ((a = (*--srcptr)) > 0xBF) return false;

        switch (*source) {
            // no fall-through in this inner switch
            case 0xE0: if (a < 0xA0) return false; break;
            case 0xED: if (a > 0x9F) return false; break;
            case 0xF0: if (a < 0x90) return false; break;
            case 0xF4: if (a > 0x8F) return false; break;
            default:   if (a < 0x80) return false;
        }

        case 1: if (*source >= 0x80 && *source < 0xC2) return false;
    }
    if (*source > 0xF4)
        return false;
    return true;
}

// Magic values subtracted from a buffer value during UTF8 conversion.
// This table contains as many values as there might be trailing bytes
// in a UTF-8 sequence.
static const UChar32 offsetsFromUTF8[6] = { 0x00000000UL, 0x00003080UL, 0x000E2080UL, 
            0x03C82080UL, 0xFA082080UL, 0x82082080UL };

ConversionResult convertUTF8ToUTF16(
    const char** sourceStart, const char* sourceEnd, 
    UChar** targetStart, UChar* targetEnd, bool strict)
{
    ConversionResult result = conversionOK;
    const char* source = *sourceStart;
    UChar* target = *targetStart;
    while (source < sourceEnd) {
        UChar32 ch = 0;
        int extraBytesToRead = UTF8SequenceLength(*source) - 1;
        if (source + extraBytesToRead >= sourceEnd) {
            result = sourceExhausted;
            break;
        }
        // Do this check whether lenient or strict
        if (!isLegalUTF8(reinterpret_cast<const unsigned char*>(source), extraBytesToRead + 1)) {
            result = sourceIllegal;
            break;
        }
        // The cases all fall through.
        switch (extraBytesToRead) {
            case 5: ch += static_cast<unsigned char>(*source++); ch <<= 6; // remember, illegal UTF-8
            case 4: ch += static_cast<unsigned char>(*source++); ch <<= 6; // remember, illegal UTF-8
            case 3: ch += static_cast<unsigned char>(*source++); ch <<= 6;
            case 2: ch += static_cast<unsigned char>(*source++); ch <<= 6;
            case 1: ch += static_cast<unsigned char>(*source++); ch <<= 6;
            case 0: ch += static_cast<unsigned char>(*source++);
        }
        ch -= offsetsFromUTF8[extraBytesToRead];

        if (target >= targetEnd) {
            source -= (extraBytesToRead + 1); // Back up source pointer!
            result = targetExhausted; break;
        }
        if (ch <= 0xFFFF) {
            // UTF-16 surrogate values are illegal in UTF-32
            if (ch >= 0xD800 && ch <= 0xDFFF) {
                if (strict) {
                    source -= (extraBytesToRead + 1); // return to the illegal value itself
                    result = sourceIllegal;
                    break;
                } else
                    *target++ = 0xFFFD;
            } else
                *target++ = (UChar)ch; // normal case
        } else if (ch > 0x10FFFF) {
            if (strict) {
                result = sourceIllegal;
                source -= (extraBytesToRead + 1); // return to the start
                break; // Bail out; shouldn't continue
            } else
                *target++ = 0xFFFD;
        } else {
            // target is a character in range 0xFFFF - 0x10FFFF
            if (target + 1 >= targetEnd) {
                source -= (extraBytesToRead + 1); // Back up source pointer!
                result = targetExhausted;
                break;
            }
            ch -= 0x0010000UL;
            *target++ = (UChar)((ch >> 10) + 0xD800);
            *target++ = (UChar)((ch & 0x03FF) + 0xDC00);
        }
    }
    *sourceStart = source;
    *targetStart = target;
    return result;
}

}
}