Changeset 568693b in mainline for uspace/lib/c/generic/str.c

Timestamp:

2012-08-17T10:24:21Z (12 years ago)

Author:

Martin Sucha <sucha14@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

20dccf3

Parents:

7d27f422

Message:

Add reverse variant of str_decode.

File:

• uspace/lib/c/generic/str.c (modified) (1 diff)

uspace/lib/c/generic/str.c

@@ -134 +134 @@
         
         return ch;
+}
+
+/** Decode a single character from a string to the left.
+ *
+ * Decode a single character from a string of size @a size. Decoding starts
+ * at @a offset and this offset is moved to the beginning of the previous
+ * character. In case of decoding error, offset generally decreases at least
+ * by one. However, offset is never moved before 0.
+ *
+ * @param str    String (not necessarily NULL-terminated).
+ * @param offset Byte offset in string where to start decoding.
+ * @param size   Size of the string (in bytes).
+ *
+ * @return Value of decoded character, U_SPECIAL on decoding error or
+ *         NULL if attempt to decode beyond @a start of str.
+ *
+ */
+wchar_t str_decode_reverse(const char *str, size_t *offset, size_t size)
+{
+        if (*offset == 0)
+                return 0;
+        
+        size_t processed = 0;
+        /* Continue while continuation bytes found */
+        while (*offset > 0 && processed < 4) {
+                uint8_t b = (uint8_t) str[--(*offset)];
+                
+                if (processed == 0 && (b & 0x80) == 0) {
+                        /* 0xxxxxxx (Plain ASCII) */
+                        return b & 0x7f;
+                }
+                else if ((b & 0xe0) == 0xc0 || (b & 0xf0) == 0xe0 ||
+                    (b & 0xf8) == 0xf0) {
+                        /* Start byte */
+                        size_t start_offset = *offset;
+                        return str_decode(str, &start_offset, size);
+                }
+                else if ((b & 0xc0) != 0x80) {
+                        /* Not a continuation byte */
+                        return U_SPECIAL;
+                }
+                processed++;
+        }
+        /* Too many continuation bytes */
+        return U_SPECIAL;
 }