Binary to hex faster than xxd, part 2 of 2

    static int hexdigit(char x)
    {
      if (x >= '0' && x <= '9') return x - '0';
      if (x >= 'a' && x <= 'f') return 10 + (x - 'a');
      if (x >= 'A' && x <= 'F') return 10 + (x - 'A');
      return -1;
    }
    int hexparse(unsigned char *y,long long len,const char *x)
    {
      if (!x) return 0;
      while (len > 0) {
        int digit0;
        int digit1;
        digit0 = hexdigit(x[0]); if (digit0 == -1) return 0;
        digit1 = hexdigit(x[1]); if (digit1 == -1) return 0;
        *y++ = digit1 + 16 * digit0;
        --len;
        x += 2;
      }
      if (x[0]) return 0;
      return 1;
    }
    char buf[256];
    long long buflen = 0;
    static void flush(void) {
        if (writeall(1, buf, buflen) == -1) _exit(errno);
        buflen = 0;
    }
    static void xeet(void) {
        flush();
        if (fsyncfd(1) == -1) _exit(errno);
        _exit(0);
    }
    static void wrch(const char ch) {
        if (buflen >= sizeof buf) flush();
        buf[buflen++] = ch;
        return;
    }
    char inbuf[128];
    int main(int argc, char **argv) {
        long long r, i;
        for (;;) {
            r = read(0, inbuf, sizeof inbuf);
            if (r == -1) _exit(errno);
            if (r == 0) break;
    
            for (i = 0; i < r; ++i) {
                wrch("0123456789abcdef"[15 & (inbuf[i] >> 4)]);
                wrch("0123456789abcdef"[15 & inbuf[i]]);
            }
        }
        wrch('\n');
        xeet();
        return 0;
    }