1 files changed, 70 insertions, 0 deletions
diff --git a/isutf8.c b/isutf8.c
new file mode 100644
index 0000000..5f63a49
--- /dev/null
+++ b/isutf8.c
@@ -0,0 +1,70 @@
+/* See LICENSE file for copyright and license details. */
+#include "libsimple.h"
+
+
+int
+libsimple_isutf8(const char *string, int allow_modified_nul)
+{
+	static long BYTES_TO_MIN_BITS[] = {0, 0,  8, 12, 17, 22, 37};
+        static long BYTES_TO_MAX_BITS[] = {0, 7, 11, 16, 21, 26, 31};
+        long int bytes = 0, read_bytes = 0, bits = 0, c, character;
+
+        /*                                                      min bits  max bits
+          0.......                                                 0         7
+          110..... 10......                                        8        11
+          1110.... 10...... 10......                              12        16
+          11110... 10...... 10...... 10......                     17        21
+          111110.. 10...... 10...... 10...... 10......            22        26
+          1111110. 10...... 10...... 10...... 10...... 10......   27        31
+        */
+
+	while ((c = (long int)(*string++))) {
+                if (!read_bytes) {
+                        /* First byte of the character. */
+
+                        if (!(c & 0x80))
+                                /* Single-byte character. */
+                                continue;
+
+                        if ((c & 0xC0) == 0x80)
+                                /* Single-byte character marked as multibyte, or
+                                   a non-first byte in a multibyte character. */
+                                return -1;
+
+                        /* Multibyte character. */
+                        while ((c & 0x80))
+                                bytes++, c <<= 1;
+                        read_bytes = 1;
+                        character = c & 0x7F;
+                        if (bytes > 6)
+                                /* 31-bit characters can be encoded with 6-bytes,
+                                   and UTF-8 does not cover higher code points. */
+                                return -1;
+                } else {
+                        /* Not first byte of the character. */
+
+                        if ((c & 0xC0) != 0x80)
+                                /* Beginning of new character before a
+                                   multibyte character has ended. */
+                                return -1;
+
+                        character = (character << 6) | (c & 0x7F);
+
+                        if (++read_bytes < bytes)
+                                /* Not at last byte yet. */
+                                continue;
+
+                        /* Check that the character is not unnecessarily long. */
+                        while (character)
+                                character >>= 1, bits++;
+                        bits = (!bits && bytes == 2 && allow_modified_nul) ? 8 : bits;
+                        if (bits < BYTES_TO_MIN_BITS[bytes] || BYTES_TO_MAX_BITS[bytes] < bits)
+                                return -1;
+
+                        read_bytes = bytes = bits = 0;
+                }
+        }
+
+        /* Make sure we did not stop at the middle of a multibyte character. */
+        return !read_bytes;
+}