--- /dev/null
+#include "gmqcc.h"
+
+/*
+ * Based on the flexible and economical utf8 decoder:
+ * http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
+ *
+ * This is slightly more economical, the fastest way to decode utf8 is
+ * with a lookup table as in:
+ *
+ * first 1-byte lookup
+ * if that fails, 2-byte lookup
+ * if that fails, 3-byte lookup
+ * if that fails, 4-byte lookup
+ *
+ * The following table can be generated with some interval trickery.
+ * consider an interval [a, b):
+ *
+ * a must be 0x80 or b must be 0xc0, lower 3 bits
+ * are clear, thus:
+ * interval(a,b) = ((uint32_t)((a==0x80?0x40-b:-a)<<23))
+ *
+ * The failstate can be represented as interval(0x80,0x80), it's
+ * odd to see but this is a full state machine.
+ *
+ * The table than maps the corresponding sections as a serise of
+ * intervals.
+ *
+ * In this table the transition values are pre-multiplied with 16 to
+ * save a shift instruction for every byte, we throw away fillers
+ * which makes the table smaller.
+ *
+ * The first section of the table handles bytes with leading C
+ * The second section of the table handles bytes with leading D
+ * The third section of the table handles bytes with leading E
+ * The last section of the table handles bytes with leading F
+ *
+ * The values themselfs in the table are arranged so that when you
+ * left shift them by 6 to shift continuation characters into place, the
+ * new top bits tell you:
+ *
+ * 1 - if you keep going
+ * 2 - the range of valid values for the next byte
+ */
+static const uint32_t utf8_tab[] = {
+ 0xC0000002, 0xC0000003, 0xC0000004, 0xC0000005, 0xC0000006,
+ 0xC0000007, 0xC0000008, 0xC0000009, 0xC000000A, 0xC000000B,
+ 0xC000000C, 0xC000000D, 0xC000000E, 0xC000000F, 0xC0000010,
+ 0xC0000011, 0xC0000012, 0xC0000013, 0xC0000014, 0xC0000015,
+ 0xC0000016, 0xC0000017, 0xC0000018, 0xC0000019, 0xC000001A,
+ 0xC000001B, 0xC000001C, 0xC000001D, 0xC000001E, 0xC000001F,
+ 0xB3000000, 0xC3000001, 0xC3000002, 0xC3000003, 0xC3000004,
+ 0xC3000005, 0xC3000006, 0xC3000007, 0xC3000008, 0xC3000009,
+ 0xC300000A, 0xC300000B, 0xC300000C, 0xD300000D, 0xC300000E,
+ 0xC300000F, 0xBB0C0000, 0xC30C0001, 0xC30C0002, 0xC30C0003,
+ 0xD30C0004
+};
+
+int utf8_from(char *s, utf8ch_t ch) {
+ if (!s)
+ return 0;
+
+ if ((unsigned)ch < 0x80) {
+ *s = ch;
+ return 1;
+ } else if ((unsigned)ch < 0x800) {
+ *s++ = 0xC0 | (ch >> 6);
+ *s = 0x80 | (ch & 0x3F);
+ return 2;
+ } else if ((unsigned)ch < 0xD800 || (unsigned)ch - 0xE000 < 0x2000) {
+ *s++ = 0xE0 | (ch >> 12);
+ *s++ = 0x80 | ((ch >> 6) & 0x3F);
+ *s = 0x80 | (ch & 0x3F);
+ return 3;
+ } else if ((unsigned)ch - 0x10000 < 0x100000) {
+ *s++ = 0xF0 | (ch >> 18);
+ *s++ = 0x80 | ((ch >> 12) & 0x3F);
+ *s++ = 0x80 | ((ch >> 6) & 0x3F);
+ *s = 0x80 | (ch & 0x3F);
+ return 4;
+ }
+ return 0;
+}
+
+int utf8_to(utf8ch_t *i, const unsigned char *s, size_t n) {
+ unsigned c,j;
+
+ if (!s || !n)
+ return 0;
+
+ /* This is consistent with mbtowc behaviour. */
+ if (!i)
+ i = (utf8ch_t*)(void*)&i;
+
+ if (*s < 0x80)
+ return !!(*i = *s);
+ if (*s-0xC2U > 0x32)
+ return 0;
+
+ c = utf8_tab[*s++-0xC2U];
+
+ /*
+ * Avoid excessive checks against n.
+ *
+ * When shifting state `n-1` times does not clear the high bit,
+ * then the value of `n` won't satisfy the condition to read a
+ * character as it will be insufficent.
+ */
+ if (n < 4 && ((c<<(6*n-6)) & (1U << 31)))
+ return 0;
+
+ /*
+ * The upper 6 state bits are negitive integer offset to a bound-check
+ * next byte equivlant to: ((b-0x80)+(b+offset))&~0x3f
+ */
+ if ((((*s>>3)-0x10)|((*s>>3)+((int32_t)c>>26))) & ~7)
+ return 0;
+
+ for (j=2; j<3; j++) {
+ if (!((c = c<<6 | (*s++-0x80))&(1U<<31))) {
+ *i = c;
+ return j;
+ }
+ if (*s-0x80U >= 0x40)
+ return 0;
+ }
+
+ *i = c<<6 | (*s++-0x80);
+ return 4;
+}