101 lines
3.1 KiB
C
101 lines
3.1 KiB
C
/*
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* Dealing with Unicode
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*
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* Copyright (C) 2013 Red Hat, Inc.
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*
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* Authors:
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* Markus Armbruster <armbru@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#include "qemu-common.h"
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/**
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* mod_utf8_codepoint:
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* @s: string encoded in modified UTF-8
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* @n: maximum number of bytes to read from @s, if less than 6
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* @end: set to end of sequence on return
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*
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* Convert the modified UTF-8 sequence at the start of @s. Modified
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* UTF-8 is exactly like UTF-8, except U+0000 is encoded as
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* "\xC0\x80".
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*
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* If @n is zero or @s points to a zero byte, the sequence is invalid,
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* and @end is set to @s.
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*
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* If @s points to an impossible byte (0xFE or 0xFF) or a continuation
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* byte, the sequence is invalid, and @end is set to @s + 1
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*
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* Else, the first byte determines how many continuation bytes are
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* expected. If there are fewer, the sequence is invalid, and @end is
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* set to @s + 1 + actual number of continuation bytes. Else, the
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* sequence is well-formed, and @end is set to @s + 1 + expected
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* number of continuation bytes.
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*
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* A well-formed sequence is valid unless it encodes a codepoint
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* outside the Unicode range U+0000..U+10FFFF, one of Unicode's 66
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* noncharacters, a surrogate codepoint, or is overlong. Except the
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* overlong sequence "\xC0\x80" is valid.
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*
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* Conversion succeeds if and only if the sequence is valid.
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*
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* Returns: the Unicode codepoint on success, -1 on failure.
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*/
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int mod_utf8_codepoint(const char *s, size_t n, char **end)
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{
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static int min_cp[5] = { 0x80, 0x800, 0x10000, 0x200000, 0x4000000 };
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const unsigned char *p;
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unsigned byte, mask, len, i;
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int cp;
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if (n == 0 || *s == 0) {
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/* empty sequence */
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*end = (char *)s;
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return -1;
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}
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p = (const unsigned char *)s;
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byte = *p++;
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if (byte < 0x80) {
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cp = byte; /* one byte sequence */
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} else if (byte >= 0xFE) {
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cp = -1; /* impossible bytes 0xFE, 0xFF */
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} else if ((byte & 0x40) == 0) {
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cp = -1; /* unexpected continuation byte */
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} else {
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/* multi-byte sequence */
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len = 0;
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for (mask = 0x80; byte & mask; mask >>= 1) {
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len++;
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}
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assert(len > 1 && len < 7);
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cp = byte & (mask - 1);
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for (i = 1; i < len; i++) {
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byte = i < n ? *p : 0;
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if ((byte & 0xC0) != 0x80) {
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cp = -1; /* continuation byte missing */
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goto out;
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}
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p++;
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cp <<= 6;
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cp |= byte & 0x3F;
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}
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if (cp > 0x10FFFF) {
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cp = -1; /* beyond Unicode range */
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} else if ((cp >= 0xFDD0 && cp <= 0xFDEF)
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|| (cp & 0xFFFE) == 0xFFFE) {
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cp = -1; /* noncharacter */
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} else if (cp >= 0xD800 && cp <= 0xDFFF) {
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cp = -1; /* surrogate code point */
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} else if (cp < min_cp[len - 2] && !(cp == 0 && len == 2)) {
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cp = -1; /* overlong, not \xC0\x80 */
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}
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}
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out:
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*end = (char *)p;
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return cp;
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}
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