New modules 'unistr/u8-prev', 'unistr/u16-prev', 'unistr/u32-prev'.

[gnulib.git] / lib / unistr / u8-prev.c

diff --git a/lib/unistr/u8-prev.c b/lib/unistr/u8-prev.c
new file mode 100644 (file)
index 0000000..b3b56dd
--- /dev/null
+++ b/lib/unistr/u8-prev.c
@@ -0,0 +1,95 @@
+/* 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 Library General Public License as published
+   by the Free Software Foundation; either version 2, 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+   USA.  */
+
+#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 utf8-ucs4.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;
+}