Support no-std builds #4
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ebfull
previously requested changes
Mar 4, 2021
Codecov Report
@@ Coverage Diff @@
## main #4 +/- ##
==========================================
- Coverage 66.50% 65.53% -0.97%
==========================================
Files 10 10
Lines 1421 1445 +24
==========================================
+ Hits 945 947 +2
- Misses 476 498 +22
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The `FieldExt` trait was originally the only trait implemented in this
crate. When we added `ff` support, we reworked `FieldExt` to be an
extension trait on top of `ff::PrimeField`, but left the existing impls
in `FieldExt`. This resulted in some circular dependencies that prevent
us from making `FieldExt` conditional (e.g. for no-std support).
This commit removes the cycles like so:
- `ff::PrimeField::{from_repr, to_repr}` were implemented as calls to
`FieldExt::{from_bytes, to_bytes}`. The field encoding/decoding logic
is moved into the `ff::PrimeField` trait impl, and `FieldExt` now
calls into `ff::PrimeField`.
- `ff::Field::sqrt` was implemented in terms of `FieldExt::sqrt_alt`.
Given that the latter is a trivial wrapper around the `SqrtTables`
implementation, we duplicate the call to eliminate the cycle.
- `ff::Field::random` used `FieldExt::from_bytes_wide`, which wraps
either `Fp::from_u512` or `Fq::from_u512`. We now use these internal
methods directly.
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We re-introduce the Tonelli-Shank square root algoritm that was removed in zcash/halo2#120, to use in no-std mode (the table-based impl requires allocations, and also uses 29kiB of memory which is a problem for constrained environments that typically need no-std).
daira
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Sep 20, 2021
daira
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Sep 20, 2021
daira
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Sep 20, 2021
Co-authored-by: Daira Hopwood <daira@jacaranda.org>
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huitseeker
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Apr 15, 2023
It doesn't affect the serialized output.
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