LXR qemu/util/unicode.c

   1/*
   2 * Dealing with Unicode
   3 *
   4 * Copyright (C) 2013 Red Hat, Inc.
   5 *
   6 * Authors:
   7 *  Markus Armbruster <armbru@redhat.com>
   8 *
   9 * This work is licensed under the terms of the GNU GPL, version 2 or
  10 * later.  See the COPYING file in the top-level directory.
  11 */
  12
  13#include "qemu/osdep.h"
  14#include "qemu/unicode.h"
  15
  16/**
  17 * mod_utf8_codepoint:
  18 * @s: string encoded in modified UTF-8
  19 * @n: maximum number of bytes to read from @s, if less than 6
  20 * @end: set to end of sequence on return
  21 *
  22 * Convert the modified UTF-8 sequence at the start of @s.  Modified
  23 * UTF-8 is exactly like UTF-8, except U+0000 is encoded as
  24 * "\xC0\x80".
  25 *
  26 * If @n is zero or @s points to a zero byte, the sequence is invalid,
  27 * and @end is set to @s.
  28 *
  29 * If @s points to an impossible byte (0xFE or 0xFF) or a continuation
  30 * byte, the sequence is invalid, and @end is set to @s + 1
  31 *
  32 * Else, the first byte determines how many continuation bytes are
  33 * expected.  If there are fewer, the sequence is invalid, and @end is
  34 * set to @s + 1 + actual number of continuation bytes.  Else, the
  35 * sequence is well-formed, and @end is set to @s + 1 + expected
  36 * number of continuation bytes.
  37 *
  38 * A well-formed sequence is valid unless it encodes a codepoint
  39 * outside the Unicode range U+0000..U+10FFFF, one of Unicode's 66
  40 * noncharacters, a surrogate codepoint, or is overlong.  Except the
  41 * overlong sequence "\xC0\x80" is valid.
  42 *
  43 * Conversion succeeds if and only if the sequence is valid.
  44 *
  45 * Returns: the Unicode codepoint on success, -1 on failure.
  46 */
  47int mod_utf8_codepoint(const char *s, size_t n, char **end)
  48{
  49    static int min_cp[5] = { 0x80, 0x800, 0x10000, 0x200000, 0x4000000 };
  50    const unsigned char *p;
  51    unsigned byte, mask, len, i;
  52    int cp;
  53
  54    if (n == 0 || *s == 0) {
  55        /* empty sequence */
  56        *end = (char *)s;
  57        return -1;
  58    }
  59
  60    p = (const unsigned char *)s;
  61    byte = *p++;
  62    if (byte < 0x80) {
  63        cp = byte;              /* one byte sequence */
  64    } else if (byte >= 0xFE) {
  65        cp = -1;                /* impossible bytes 0xFE, 0xFF */
  66    } else if ((byte & 0x40) == 0) {
  67        cp = -1;                /* unexpected continuation byte */
  68    } else {
  69        /* multi-byte sequence */
  70        len = 0;
  71        for (mask = 0x80; byte & mask; mask >>= 1) {
  72            len++;
  73        }
  74        assert(len > 1 && len < 7);
  75        cp = byte & (mask - 1);
  76        for (i = 1; i < len; i++) {
  77            byte = i < n ? *p : 0;
  78            if ((byte & 0xC0) != 0x80) {
  79                cp = -1;        /* continuation byte missing */
  80                goto out;
  81            }
  82            p++;
  83            cp <<= 6;
  84            cp |= byte & 0x3F;
  85        }
  86        if (cp > 0x10FFFF) {
  87            cp = -1;            /* beyond Unicode range */
  88        } else if ((cp >= 0xFDD0 && cp <= 0xFDEF)
  89                   || (cp & 0xFFFE) == 0xFFFE) {
  90            cp = -1;            /* noncharacter */
  91        } else if (cp >= 0xD800 && cp <= 0xDFFF) {
  92            cp = -1;            /* surrogate code point */
  93        } else if (cp < min_cp[len - 2] && !(cp == 0 && len == 2)) {
  94            cp = -1;            /* overlong, not \xC0\x80 */
  95        }
  96    }
  97
  98out:
  99    *end = (char *)p;
 100    return cp;
 101}
 102