[tor-dev] curve25519_donna vs. crypto_scalarmult_curve25519?

[Steve Snyder]

Given a contemporary release of Tor with a contemporary version of OpenSSL, under what circumstances is the intrinsic curve25519_donna() preferred over the libsodium/NaCl crypto_scalarmult_curve25519(), or vice versa?

Does it come down to 32-bit vs. 64-bit?  Or CPU instruction sets detected at build time?

Or has libsodium/NaCl been deprecated altogether and just not removed from the configure script?

I'm trying to determine if installation of libsodium in a Tor build environment will yield a "better" Tor binary.

Thanks.