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/src/utf8_size.c (raw)

#include <stdint.h>
#include <stddef.h>
#include "unicode.h"

struct {
	uint8_t mask;
	uint8_t result;
	int octets;
} sizes[] = {
	{ 0x80, 0x00, 1 },
	{ 0xE0, 0xC0, 2 },
	{ 0xF0, 0xE0, 3 },
	{ 0xF8, 0xF0, 4 },
	{ 0xFC, 0xF8, 5 },
	{ 0xFE, 0xF8, 6 },
	{ 0x80, 0x80, -1 },
};

int utf8_size(const char *s) {
	uint8_t c = (uint8_t)*s;
	for (size_t i = 0; i < sizeof(sizes) / 2; ++i) {
		if ((c & sizes[i].mask) == sizes[i].result) {
			return sizes[i].octets;
		}
	}
	return -1;
}