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Add associated constants of type Self to Field and PrimeField #94

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merged 1 commit into from
Nov 2, 2022
Merged

Add associated constants of type Self to Field and PrimeField #94

merged 1 commit into from
Nov 2, 2022

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str4d
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@str4d str4d commented Oct 28, 2022

We now require that the type implementing Field, and its particular values for these constants, can be constructed in a const context. Once upon a time this might have been onerous, but it should now be a reasonable requirement given our MSRV of 1.56.0.

Closes #87.

@str4d str4d mentioned this pull request Oct 28, 2022
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str4d commented Oct 28, 2022 •
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Prior to merging this, I want to confirm that the major implementors of the ff traits are able to implement these associated constants. Here is the list of crates I know about, and which ones I have confirmed can migrate to providing associated constants:

  • bls12_381
  • jubjub
  • pasta_curves
  • blstrs
  • ec-gpu-gen
  • Rust Crypto crates:
    • k256
    • p256
    • p384
    • bp256
    • bp384
  • TODO: find more crates

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@str4d the @RustCrypto crates are all fine. They support both const fn constructors and arithmetic on their respective FieldElement and Scalar types.

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str4d commented Oct 31, 2022

I confirmed that blstrs implements the current trait methods using constants, so can migrate to associated constants. And AFAICT ec-gpu-gen only uses the representation parts of the ff traits to shuttle field elements between CPU and GPU; it doesn't actually generate code that implements Field or PrimeField. So I think I'm satisfied that this PR is fine.

@str4d str4d marked this pull request as ready for review October 31, 2022 08:29
daira
daira approved these changes Oct 31, 2022
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utACK

ebfull
ebfull requested changes Nov 2, 2022
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Base automatically changed from field-trait-changes to main November 2, 2022 18:55
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str4d commented Nov 2, 2022

Rebased on main to fix merge conflicts and address @ebfull's comment.

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Use associated constants of type Self in Field and PrimeField
6bf93ee 
We now require that the type implementing `Field`, and its particular
values for these constants, can be constructed in a const context. Once
upon a time this might have been onerous, but it should now be a
reasonable requirement given our MSRV of 1.56.0.

Closes #87.
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str4d commented Nov 2, 2022

Force-pushed to fix a documentation lint.

@str4d str4d merged commit 1eddf54 into main Nov 2, 2022
@str4d str4d deleted the trait-constants branch November 2, 2022 20:42
@str4d str4d mentioned this pull request Nov 2, 2022
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@daira daira daira approved these changes

@ebfull ebfull ebfull approved these changes

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Consider promoting Field::{zero, one} to associated constants
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@str4d @tarcieri @daira @ebfull