utf8strlen.c

#include <stdlib.h>

unsigned long utf8_strlen(unsigned char *s) {
    unsigned long len = 0;
    s--;
    while (*++s) {
        len += !(*s >> 7) || (*s >> 6);
    }
    return len;
}

int main() {
    for (int i = 0; i < 10000000; i++) {
        utf8_strlen("hello world");
        utf8_strlen("héllo world");
        utf8_strlen("héłlo world");
    }
}