static void mult(long[] output, long[] in, long[] in2) {
    long[] t = new long[19];
    product(t, in, in2);
    // |t[i]| < 2^26
    reduce(t, output);
  }
A helpful wrapper around {@ref Field25519#product}: output = in * in2.

<p>On entry: |in[i]| < 2^27 and |in2[i]| < 2^27.

<p>The output is reduced degree (indeed, one need only provide storage for 10 limbs) and
|output[i]| < 2^26.
java_src/src/main/java/com/google/crypto/tink/internal/Field25519.java