ff: More trait refactoring#228
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The sqrt() function is now part of the Field trait. ff_derive returns an error on fields for which it does not support generating a square root function. Note that Fq6 and Fq12 in pairing::bls12_381 leave the function unimplemented. They will be dropped once the migration to the bls12_381 crate is complete. The equivalent structs in that crate are not exposed.
It is only used internally in the bls12_381 crate, and field extensions aren't exposed anywhere in the Zcash stack.
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@@ Coverage Diff @@
## master #228 +/- ##
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- Coverage 65.25% 65.24% -0.02%
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Files 106 106
Lines 15057 14977 -80
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- Hits 9825 9771 -54
+ Misses 5232 5206 -26
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This enables generic code to reliably operate on the bits of an encoded field element, by converting them to and from a known (little) endianness. The BitAnd and Shr bounds on PrimeField are now removed, as users can perform these operations themselves as needed.
ff_derive still implements Ord and PartialOrd for the fields it implements, because pairing::bls12_381 internally assumes that those are implemented. Once we delete that implementation, we will remove the Ord and PartialOrd implementations from ff_derive.
The only places we don't use constant u64 limbs, we use PrimeField::char instead (except in a single test where we use a field element).
Now that PrimeField::ReprEndianness exists, users can obtain a known-endianness representation from the output of PrimeField::char (which is a PrimeField::Repr, and should return a representation with the same endianness as PrimeField::into_repr).
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str4d
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May 5, 2020
| /// specific endianness. This is useful when you need to act on the bit representation | ||
| /// of an element generically, as the native binary representation of a prime field is | ||
| /// field-dependent. | ||
| pub trait Endianness: ByteOrder { |
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This could be renamed ByteOrderExt if we workshop its API to be more widely useful, but it can only be implemented for byteorder::{BigEndian, LittleEndian} because byteorder::ByteOrder is sealed, so the only effect this has on end users is the import they use to access the APIs.
ebfull
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May 12, 2020
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Add Slack PR notifier for upstream Zcash contributions
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Addresses trait-related comments from @ebfull on #227.