Replace mp_mod_inv with recip
#233
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This replaces the `mp_mod_inv` function with `recip`. The latter uses the `Field` instance for `Z p` and is thus safer than `mp_mod_inv`, as it requires that `p` is prime. This is the only real call site of `mp_mod_inv`, so we can remove `mp_mod_inv` in a follow-up commit.
`mp_mod_inv` has an incorrect type signature, as it is only valid when the
modulus is prime, but the type does not reflect this. Moreover, there is now a
correct version of this in the Cryptol prelude in the form of `recip : {p}
(prime p) => Z p -> Z p`, so there is really no need to define `mp_mod_inv`
separately anymore. Let's just remove `mp_mod_inv`.
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When I wrote that function 7 years ago (!) we didn't have a |
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Closes #100.
mp_mod_invhas an incorrect type signature, as it is only valid when the modulus is prime, but the type does not reflect this. Moreover, there is now a correct version of this in the Cryptol prelude in the form ofrecip : {p} (prime p) => Z p -> Z p, so there is really no need to definemp_mod_invseparately anymore. Let's just removemp_mod_inv.The only real call site for
mp_mod_invwas inCommon::EC::PrimeField::PFEC, but it is easily swapped out forrecip.