Convert ISO-8859-1 to UTF-8 with constant RAM (cf iconv)

latin2utf.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#define MAX 4096

void die(const char *s) {
        perror(s);
        exit(1);
}

int convert(int fd_in, int fd_out) {
        char buffer[MAX];
        char output[MAX*2];
        int bytes;
        char *i, *o;

        while(0 < (bytes = read(STDIN_FILENO, buffer, MAX))) {
                if(bytes == -1) { die("read"); }

                for(i = buffer, o = output; i < buffer + bytes; i++, o++) {
                        if(*i & 0x80) {
                                *o = 0xc0 | ((*i & 0xc0) >> 6);
                                o++;
                                *o = 0x80 |  (*i & 0x3f);
                        } else {
                                *o = *i;
                        }
                }

                bytes = write(STDOUT_FILENO, output, o - output);

                if (bytes == -1) { die("write"); }
        }
        return 0;
}

int main(int argc, char *argv[], char *env[]) {
        exit(convert(STDIN_FILENO, STDOUT_FILENO));
}