u8decode.h


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

#include <stdint.h>

// Decode one UTF-8 codepoint into cp, return number of bytes to next one.
// On invalid UTF-8, return -1, and do not change cp.
// Overlong sequences, surrogates and invalid codepoints are not checked.
//
// This code is meant to be inlined, if cp is unused it can be optimized away.
static int
u8decode(const char *cs, uint32_t *cp)
{
	const uint8_t *s = (uint8_t *)cs;

	if (*s == 0)   { *cp = 0; return 0; }
	if (*s < 0x80) { *cp = *s; return 1; }
	if (*s < 0xc0) { return -1; }
	if (*s < 0xe0) { *cp = *s & 0x1f; goto u2; }
	if (*s < 0xf0) { *cp = *s & 0x0f; goto u3; }
	if (*s < 0xf8) { *cp = *s & 0x07; goto u4; }
	return -1;

u4:	if ((*++s & 0xc0) != 0x80) return -1;  *cp = (*cp << 6) | (*s & 0x3f);
u3:	if ((*++s & 0xc0) != 0x80) return -1;  *cp = (*cp << 6) | (*s & 0x3f);
u2:	if ((*++s & 0xc0) != 0x80) return -1;  *cp = (*cp << 6) | (*s & 0x3f);
	return s - (uint8_t *)cs + 1;
}