fdifference       406 crypto/curve25519-donna.c   fdifference(z, origx);  // does x - z
fdifference       410 crypto/curve25519-donna.c   fdifference(zprime, origxprime);
fdifference       419 crypto/curve25519-donna.c   fdifference(zzprime, origxprime);
fdifference       433 crypto/curve25519-donna.c   fdifference(zz, xx);  // does zz = xx - zz