1 /* Iterate over previous character in UTF-8 string. 2 Copyright (C) 2002, 2006-2007, 2009-2014 Free Software Foundation, Inc. 3 Written by Bruno Haible <bruno@clisp.org>, 2002. 4 5 This program is free software: you can redistribute it and/or modify it 6 under the terms of the GNU Lesser General Public License as published 7 by the Free Software Foundation; either version 3 of the License, or 8 (at your option) any later version. 9 10 This program is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public License 16 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 17 18 #include <config.h> 19 20 /* Specification. */ 21 #include "unistr.h" 22 23 const uint8_t * 24 u8_prev (ucs4_t *puc, const uint8_t *s, const uint8_t *start) 25 { 26 /* Keep in sync with unistr.h and u8-mbtouc-aux.c. */ 27 if (s != start) 28 { 29 uint8_t c_1 = s[-1]; 30 31 if (c_1 < 0x80) 32 { 33 *puc = c_1; 34 return s - 1; 35 } 36 #if CONFIG_UNICODE_SAFETY 37 if ((c_1 ^ 0x80) < 0x40) 38 #endif 39 if (s - 1 != start) 40 { 41 uint8_t c_2 = s[-2]; 42 43 if (c_2 >= 0xc2 && c_2 < 0xe0) 44 { 45 *puc = ((unsigned int) (c_2 & 0x1f) << 6) 46 | (unsigned int) (c_1 ^ 0x80); 47 return s - 2; 48 } 49 #if CONFIG_UNICODE_SAFETY 50 if ((c_2 ^ 0x80) < 0x40) 51 #endif 52 if (s - 2 != start) 53 { 54 uint8_t c_3 = s[-3]; 55 56 if (c_3 >= 0xe0 && c_3 < 0xf0 57 #if CONFIG_UNICODE_SAFETY 58 && (c_3 >= 0xe1 || c_2 >= 0xa0) 59 && (c_3 != 0xed || c_2 < 0xa0) 60 #endif 61 ) 62 { 63 *puc = ((unsigned int) (c_3 & 0x0f) << 12) 64 | ((unsigned int) (c_2 ^ 0x80) << 6) 65 | (unsigned int) (c_1 ^ 0x80); 66 return s - 3; 67 } 68 #if CONFIG_UNICODE_SAFETY 69 if ((c_3 ^ 0x80) < 0x40) 70 #endif 71 if (s - 3 != start) 72 { 73 uint8_t c_4 = s[-4]; 74 75 if (c_4 >= 0xf0 && c_4 < 0xf8 76 #if CONFIG_UNICODE_SAFETY 77 && (c_4 >= 0xf1 || c_3 >= 0x90) 78 && (c_4 < 0xf4 || (c_4 == 0xf4 && c_3 < 0x90)) 79 #endif 80 ) 81 { 82 *puc = ((unsigned int) (c_4 & 0x07) << 18) 83 | ((unsigned int) (c_3 ^ 0x80) << 12) 84 | ((unsigned int) (c_2 ^ 0x80) << 6) 85 | (unsigned int) (c_1 ^ 0x80); 86 return s - 4; 87 } 88 } 89 } 90 } 91 } 92 return NULL; 93 } 94