diff options
Diffstat (limited to 'lib/unistr/u8-prev.c')
| -rw-r--r-- | lib/unistr/u8-prev.c | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/lib/unistr/u8-prev.c b/lib/unistr/u8-prev.c new file mode 100644 index 0000000..245d22f --- /dev/null +++ b/lib/unistr/u8-prev.c @@ -0,0 +1,93 @@ +/* Iterate over previous character in UTF-8 string. + Copyright (C) 2002, 2006-2007 Free Software Foundation, Inc. + Written by Bruno Haible <bruno@clisp.org>, 2002. + + This program is free software: you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published + by the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* Specification. */ +#include "unistr.h" + +const uint8_t * +u8_prev (ucs4_t *puc, const uint8_t *s, const uint8_t *start) +{ + /* Keep in sync with unistr.h and utf8-ucs4.c. */ + if (s != start) + { + uint8_t c_1 = s[-1]; + + if (c_1 < 0x80) + { + *puc = c_1; + return s - 1; + } +#if CONFIG_UNICODE_SAFETY + if ((c_1 ^ 0x80) < 0x40) +#endif + if (s - 1 != start) + { + uint8_t c_2 = s[-2]; + + if (c_2 >= 0xc2 && c_2 < 0xe0) + { + *puc = ((unsigned int) (c_2 & 0x1f) << 6) + | (unsigned int) (c_1 ^ 0x80); + return s - 2; + } +#if CONFIG_UNICODE_SAFETY + if ((c_2 ^ 0x80) < 0x40) +#endif + if (s - 2 != start) + { + uint8_t c_3 = s[-3]; + + if (c_3 >= 0xe0 && c_3 < 0xf0 +#if CONFIG_UNICODE_SAFETY + && (c_3 >= 0xe1 || c_2 >= 0xa0) + && (c_3 != 0xed || c_2 < 0xa0) +#endif + ) + { + *puc = ((unsigned int) (c_3 & 0x0f) << 12) + | ((unsigned int) (c_2 ^ 0x80) << 6) + | (unsigned int) (c_1 ^ 0x80); + return s - 3; + } +#if CONFIG_UNICODE_SAFETY + if ((c_3 ^ 0x80) < 0x40) +#endif + if (s - 3 != start) + { + uint8_t c_4 = s[-4]; + + if (c_4 >= 0xf0 && c_4 < 0xf8 +#if CONFIG_UNICODE_SAFETY + && (c_4 >= 0xf1 || c_3 >= 0x90) + && (c_4 < 0xf4 || (c_4 == 0xf4 && c_3 < 0x90)) +#endif + ) + { + *puc = ((unsigned int) (c_4 & 0x07) << 18) + | ((unsigned int) (c_3 ^ 0x80) << 12) + | ((unsigned int) (c_2 ^ 0x80) << 6) + | (unsigned int) (c_1 ^ 0x80); + return s - 4; + } + } + } + } + } + return NULL; +} |