unicode.c

/*
 * Dealing with Unicode
 *
 * Copyright (C) 2013 Red Hat, Inc.
 *
 * Authors:
 *  Markus Armbruster <armbru@redhat.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or
 * later.  See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"
#include "qemu/unicode.h"

static bool is_valid_codepoint(int codepoint)
{
    if (codepoint > 0x10FFFFu) {
        return false;            /* beyond Unicode range */
    }
    if ((codepoint >= 0xFDD0 && codepoint <= 0xFDEF)
        || (codepoint & 0xFFFE) == 0xFFFE) {
        return false;            /* noncharacter */
    }
    if (codepoint >= 0xD800 && codepoint <= 0xDFFF) {
        return false;            /* surrogate code point */
    }
    return true;
}

/**
 * mod_utf8_codepoint:
 * @s: string encoded in modified UTF-8
 * @n: maximum number of bytes to read from @s, if less than 6
 * @end: set to end of sequence on return
 *
 * Convert the modified UTF-8 sequence at the start of @s.  Modified
 * UTF-8 is exactly like UTF-8, except U+0000 is encoded as
 * "\xC0\x80".
 *
 * If @n is zero or @s points to a zero byte, the sequence is invalid,
 * and @end is set to @s.
 *
 * If @s points to an impossible byte (0xFE or 0xFF) or a continuation
 * byte, the sequence is invalid, and @end is set to @s + 1
 *
 * Else, the first byte determines how many continuation bytes are
 * expected.  If there are fewer, the sequence is invalid, and @end is
 * set to @s + 1 + actual number of continuation bytes.  Else, the
 * sequence is well-formed, and @end is set to @s + 1 + expected
 * number of continuation bytes.
 *
 * A well-formed sequence is valid unless it encodes a codepoint
 * outside the Unicode range U+0000..U+10FFFF, one of Unicode's 66
 * noncharacters, a surrogate codepoint, or is overlong.  Except the
 * overlong sequence "\xC0\x80" is valid.
 *
 * Conversion succeeds if and only if the sequence is valid.
 *
 * Returns: the Unicode codepoint on success, -1 on failure.
 */
int mod_utf8_codepoint(const char *s, size_t n, char **end)
{
    static int min_cp[5] = { 0x80, 0x800, 0x10000, 0x200000, 0x4000000 };
    const unsigned char *p;
    unsigned byte, mask, len, i;
    int cp;

    if (n == 0 || *s == 0) {
        /* empty sequence */
        *end = (char *)s;
        return -1;
    }

    p = (const unsigned char *)s;
    byte = *p++;
    if (byte < 0x80) {
        cp = byte;              /* one byte sequence */
    } else if (byte >= 0xFE) {
        cp = -1;                /* impossible bytes 0xFE, 0xFF */
    } else if ((byte & 0x40) == 0) {
        cp = -1;                /* unexpected continuation byte */
    } else {
        /* multi-byte sequence */
        len = 0;
        for (mask = 0x80; byte & mask; mask >>= 1) {
            len++;
        }
        assert(len > 1 && len < 7);
        cp = byte & (mask - 1);
        for (i = 1; i < len; i++) {
            byte = i < n ? *p : 0;
            if ((byte & 0xC0) != 0x80) {
                cp = -1;        /* continuation byte missing */
                goto out;
            }
            p++;
            cp <<= 6;
            cp |= byte & 0x3F;
        }
        if (!is_valid_codepoint(cp)) {
            cp = -1;
        } else if (cp < min_cp[len - 2] && !(cp == 0 && len == 2)) {
            cp = -1;            /* overlong, not \xC0\x80 */
        }
    }

out:
    *end = (char *)p;
    return cp;
}

/**
 * mod_utf8_encode:
 * @buf: Destination buffer
 * @bufsz: size of @buf, at least 5.
 * @codepoint: Unicode codepoint to encode
 *
 * Convert Unicode codepoint @codepoint to modified UTF-8.
 *
 * Returns: the length of the UTF-8 sequence on success, -1 when
 * @codepoint is invalid.
 */
ssize_t mod_utf8_encode(char buf[], size_t bufsz, int codepoint)
{
    assert(bufsz >= 5);

    if (!is_valid_codepoint(codepoint)) {
        return -1;
    }

    if (codepoint > 0 && codepoint <= 0x7F) {
        buf[0] = codepoint & 0x7F;
        buf[1] = 0;
        return 1;
    }
    if (codepoint <= 0x7FF) {
        buf[0] = 0xC0 | ((codepoint >> 6) & 0x1F);
        buf[1] = 0x80 | (codepoint & 0x3F);
        buf[2] = 0;
        return 2;
    }
    if (codepoint <= 0xFFFF) {
        buf[0] = 0xE0 | ((codepoint >> 12) & 0x0F);
        buf[1] = 0x80 | ((codepoint >> 6) & 0x3F);
        buf[2] = 0x80 | (codepoint & 0x3F);
        buf[3] = 0;
        return 3;
    }
    buf[0] = 0xF0 | ((codepoint >> 18) & 0x07);
    buf[1] = 0x80 | ((codepoint >> 12) & 0x3F);
    buf[2] = 0x80 | ((codepoint >> 6) & 0x3F);
    buf[3] = 0x80 | (codepoint & 0x3F);
    buf[4] = 0;
    return 4;
}