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feat: (bb) remove redundant constraints on field/group elements when using goblin plonk #8409
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a99a244
oink alpha challenges are now generated simultaneously instead of one…
zac-williamson 5eaab18
split biggroup_goblin into a distinct class and renamed `biggroup` in…
zac-williamson a18be4f
compiler fixes, namespace changes
zac-williamson 7b5d591
comments, changes
zac-williamson 33f2e5a
fix rebase error
zac-williamson c757190
rebase fixes
zac-williamson bd708ab
comments, more rebase fixes
zac-williamson f8875a8
fixed goblin_field error where wrong constant was being used
zac-williamson 6de4b04
cleanup
zac-williamson 12aaebd
comment fix
zac-williamson b1806ec
Merge branch 'master' into zw/biggroup_goblin
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114 changes: 114 additions & 0 deletions
114
barretenberg/cpp/src/barretenberg/stdlib/primitives/bigfield/goblin_field.hpp
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,114 @@ | ||
| #pragma once | ||
| #include "../bigfield/bigfield.hpp" | ||
| #include "../circuit_builders/circuit_builders_fwd.hpp" | ||
| #include "../field/field.hpp" | ||
|
|
||
| namespace bb::stdlib { | ||
|
|
||
| /** | ||
| * @brief goblin_field wraps x/y coordinates of bn254 group elements when using goblin | ||
| * @details this class exists because we do not want to parametrise goblin bn254 coordinates with bigfield. | ||
| * bigfield generates a large number of constraints to apply checks that are not needed for goblin coordinates | ||
| * This is because, in the goblin context we can apply the following heuristics: | ||
| * 1. goblin coordinate field elements are range-constrained in the Translator circuit (no need to range | ||
| * constrain here) | ||
| * 2. field elements that come out of the ECCVM are well-formed, we do not need to call `assert_is_in_field` | ||
| * 3. there should be no need to apply arithmetic to goblin coordinate field elements in-circuit | ||
| * Having a distinct class for `goblin_field` allows us to harvest these optimisations without a proliferation | ||
| * of edge cases and bloated logic in other classes | ||
| * @tparam Builder | ||
| */ | ||
| template <class Builder> class goblin_field { | ||
| public: | ||
| static constexpr uint1024_t DEFAULT_MAXIMUM_REMAINDER = | ||
| bigfield<Builder, bb::Bn254FqParams>::DEFAULT_MAXIMUM_REMAINDER; | ||
| static constexpr size_t NUM_LIMBS = bigfield<Builder, bb::Bn254FqParams>::NUM_LIMBS; | ||
| static constexpr size_t NUM_LIMB_BITS = bigfield<Builder, bb::Bn254FqParams>::NUM_LIMB_BITS; | ||
| static constexpr size_t NUM_LAST_LIMB_BITS = bigfield<Builder, bb::Bn254FqParams>::NUM_LAST_LIMB_BITS; | ||
|
|
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| using field_ct = stdlib::field_t<Builder>; | ||
| using bool_ct = stdlib::bool_t<Builder>; | ||
| std::array<field_ct, 2> limbs; | ||
|
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| // constructors mirror bigfield constructors | ||
| goblin_field() | ||
| : limbs{ 0, 0 } | ||
| {} | ||
| goblin_field(Builder* parent_context, const uint256_t& value) | ||
| { | ||
| (*this) = goblin_field(bb::fq(value)); | ||
| limbs[0].context = parent_context; | ||
| limbs[1].context = parent_context; | ||
| } | ||
| goblin_field(bb::fq input) | ||
| { | ||
| uint256_t converted(input); | ||
| uint256_t lo_v = converted.slice(0, NUM_LIMB_BITS * 2); | ||
| uint256_t hi_v = converted.slice(NUM_LIMB_BITS * 2, NUM_LIMB_BITS * 3 + NUM_LAST_LIMB_BITS); | ||
| limbs = { bb::fr(lo_v), bb::fr(hi_v) }; | ||
| } | ||
| goblin_field(field_ct lo, field_ct hi) | ||
| : limbs{ lo, hi } | ||
| {} | ||
|
|
||
| // N.B. this method is because AggregationState expects group element coordinates to be split into 4 slices | ||
| // (we could update to only use 2 for Mega but that feels complex) | ||
| goblin_field(field_ct lolo, field_ct lohi, field_ct hilo, field_ct hihi, [[maybe_unused]] bool can_overflow = false) | ||
| : limbs{ lolo + lohi * (uint256_t(1) << NUM_LIMB_BITS), hilo + hihi * (uint256_t(1) << NUM_LIMB_BITS) } | ||
| {} | ||
|
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||
| void assert_equal(const goblin_field& other) const | ||
| { | ||
| limbs[0].assert_equal(other.limbs[0]); | ||
| limbs[1].assert_equal(other.limbs[1]); | ||
| } | ||
| static goblin_field zero() { return goblin_field{ 0, 0 }; } | ||
|
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| static goblin_field from_witness(Builder* ctx, bb::fq input) | ||
| { | ||
| uint256_t converted(input); | ||
| uint256_t lo_v = converted.slice(0, NUM_LIMB_BITS * 2); | ||
| uint256_t hi_v = converted.slice(NUM_LIMB_BITS * 2, NUM_LIMB_BITS * 3 + NUM_LAST_LIMB_BITS); | ||
| field_ct lo = field_ct::from_witness(ctx, lo_v); | ||
| field_ct hi = field_ct::from_witness(ctx, hi_v); | ||
| return goblin_field(lo, hi); | ||
| } | ||
|
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| static goblin_field conditional_assign(const bool_ct& predicate, const goblin_field& lhs, goblin_field& rhs) | ||
| { | ||
| goblin_field result; | ||
| result.limbs = { | ||
| field_ct::conditional_assign(predicate, lhs.limbs[0], rhs.limbs[0]), | ||
| field_ct::conditional_assign(predicate, lhs.limbs[1], rhs.limbs[1]), | ||
| }; | ||
| return result; | ||
| } | ||
|
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| // matches the interface for bigfield | ||
| uint512_t get_value() const | ||
| { | ||
| uint256_t lo = limbs[0].get_value(); | ||
| uint256_t hi = limbs[1].get_value(); | ||
| uint256_t result = lo + (hi << 136); | ||
| return result; | ||
| } | ||
|
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||
| // matches the interface for bigfield | ||
| uint512_t get_maximum_value() const { return (*this).get_value(); } | ||
|
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| Builder* get_context() const | ||
| { | ||
| if (limbs[0].get_context()) { | ||
| return limbs[0].get_context(); | ||
| } | ||
| return limbs[1].get_context(); | ||
| } | ||
|
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| // done in the translator circuit | ||
| void assert_is_in_field(){}; | ||
| }; | ||
| template <typename C> inline std::ostream& operator<<(std::ostream& os, goblin_field<C> const& v) | ||
| { | ||
| return os << "{ " << v.limbs[0] << " , " << v.limbs[1] << " }"; | ||
| } | ||
| } // namespace bb::stdlib | ||
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Thanks, this is good cleanup.