bb::stdlib::StdlibCodec< Field > Class Template Reference

#include <field_conversion.hpp>

Public Types
using	DataType = Field
using	Builder = typename Field::Builder
using	fr = field_t< Builder >
using	fq = bigfield< Builder, bb::Bn254FqParams >
using	bn254_commitment = element< Builder, fq, fr, curve::BN254::Group >
using	grumpkin_commitment = cycle_group< Builder >

Static Public Member Functions
template<typename T >
static T	convert_short_challenge (const fr &challenge)
	A stdlib Transcript method needed to convert a short fr challenge limb to a bigfield one.
template<typename T >
static T	convert_full_challenge (const fr &challenge)
	Convert a full-width challenge to a target type (fr or fq).
static std::vector< fr >	convert_goblin_fr_to_bn254_frs (const goblin_field< Builder > &input)
static std::vector< fr >	convert_grumpkin_fr_to_bn254_frs (const fq &input)
template<typename T >
static constexpr size_t	calc_num_fields ()
	Calculates the size of a type (in its native form) in terms of frs.
template<typename T >
static T	deserialize_from_fields (std::span< const fr > fr_vec)
	Core stdlib Transcript deserialization method.
template<typename T >
static std::vector< fr >	serialize_to_fields (const T &val)
	Core stdlib Transcript serialization method.
static std::array< fr, 2 >	split_challenge (const fr &challenge)
	Split a challenge field element into two equal-width challenges.
template<typename TargetType >
static TargetType	deserialize_from_frs (std::span< fr > elements, size_t &num_frs_read)
	A stdlib VerificationKey-specific method.

Detailed Description

template<typename Field>
class bb::stdlib::StdlibCodec< Field >

Definition at line 27 of file field_conversion.hpp.

Member Typedef Documentation

bn254_commitment

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::bn254_commitment = element<Builder, fq, fr, curve::BN254::Group>

Definition at line 33 of file field_conversion.hpp.

Builder

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::Builder = typename Field::Builder

Definition at line 30 of file field_conversion.hpp.

DataType

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::DataType = Field

Definition at line 29 of file field_conversion.hpp.

fq

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::fq = bigfield<Builder, bb::Bn254FqParams>

Definition at line 32 of file field_conversion.hpp.

fr

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::fr = field_t<Builder>

Definition at line 31 of file field_conversion.hpp.

grumpkin_commitment

template<typename Field >

using bb::stdlib::StdlibCodec< Field >::grumpkin_commitment = cycle_group<Builder>

Definition at line 34 of file field_conversion.hpp.

Member Function Documentation

calc_num_fields()

template<typename Field >

template<typename T >

static constexpr size_t bb::stdlib::StdlibCodec< Field >::calc_num_fields ( )

inlinestaticconstexpr

Calculates the size of a type (in its native form) in terms of frs.

Definition at line 101 of file field_conversion.hpp.

convert_full_challenge()

template<typename Field >

template<typename T >

static T bb::stdlib::StdlibCodec< Field >::convert_full_challenge ( const fr &  challenge )

inlinestatic

Convert a full-width challenge to a target type (fr or fq).

For fq the full challenge is decomposed into the low/high halves expected by the bigfield(low_bits, high_bits) constructor (which range-constrains the limbs), and the decomposition is bound back to the challenge so the resulting cycle scalar equals the squeezed challenge. This is exact and canonical: the challenge value is < r < q, so it is always a valid fq element. Mirrors the native FrCodec::convert_full_challenge, which reinterprets the same value as fq.

Definition at line 70 of file field_conversion.hpp.

convert_goblin_fr_to_bn254_frs()

template<typename Field >

static std::vector< fr > bb::stdlib::StdlibCodec< Field >::convert_goblin_fr_to_bn254_frs ( const goblin_field< Builder > &  input )

inlinestatic

Definition at line 82 of file field_conversion.hpp.

convert_grumpkin_fr_to_bn254_frs()

template<typename Field >

static std::vector< fr > bb::stdlib::StdlibCodec< Field >::convert_grumpkin_fr_to_bn254_frs ( const fq &  input )

inlinestatic

Definition at line 87 of file field_conversion.hpp.

convert_short_challenge()

template<typename Field >

template<typename T >

static T bb::stdlib::StdlibCodec< Field >::convert_short_challenge ( const fr &  challenge )

inlinestatic

A stdlib Transcript method needed to convert a short fr challenge limb to a bigfield one.

Template Parameters

T

fr or fq

Parameters

challenge

a 127-bit limb of a full challenge

Returns

T

Definition at line 43 of file field_conversion.hpp.

deserialize_from_fields()

template<typename Field >

template<typename T >

static T bb::stdlib::StdlibCodec< Field >::deserialize_from_fields ( std::span< const fr >  fr_vec )

inlinestatic

Core stdlib Transcript deserialization method.

Deserializes a vector of in-circuit frs, i.e. field_t elements, into

• field_t — no conversion needed
• bigfield — 2 input field_ts are fed into bigfield constructor, then assert_is_in_field() is called to reject aliased values (>= Fq::modulus). This ensures consistency with native FrCodec which also rejects aliases. Specific to UltraCircuitBuilder.
• goblin field element — stores limbs as-is without in-circuit modulus check. Range constraints are deferred to Translator circuit (see Translator Range Constraint relation). TODO(https://github.com/AztecProtocol/barretenberg/issues/1607): Translator only enforces <254-bit constraints, NOT strict <q checks, creating verification inconsistency with native/Ultra. Specific to MegaCircuitBuilder.
• bn254 goblin point — input vector of size 4 is transformed into a pair of goblin_field elements, which are fed into the 2-arg constructor. Point-at-infinity is represented as (0, 0) and validated by ECCVM (see ECCVM Transcript relation). Specific to MegaCircuitBuilder.
• bn254 point — reconstruct a pair of bigfield elements (x, y), check whether the resulting point is a point at infinity and ensure it lies on the curve. Specific to UltraCircuitBuilder.
• Grumpkin point — since the grumpkin base field is fr, the reconstruction is trivial. We check in-circuit whether the resulting point lies on the curve and whether it is a point at infinity. Specific to UltraCircuitBuilder.
• Univariate or a std::array of elements of the above types.

Template Parameters

Builder	UltraCircuitBuilder or MegaCircuitBuilder
T	Target object type

Parameters

fr_vec

Input field_t elements

Definition at line 151 of file field_conversion.hpp.

deserialize_from_frs()

template<typename Field >

template<typename TargetType >

static TargetType bb::stdlib::StdlibCodec< Field >::deserialize_from_frs ( std::span< fr >  elements, size_t &  num_frs_read  )

inlinestatic

A stdlib VerificationKey-specific method.

Deserialize an object of specified type from a buffer of field elements; update provided read count in place

Template Parameters

TargetType

Type to reconstruct from buffer of field elements

Parameters

elements	Buffer of field_t elements
num_frs_read	Index at which to read into buffer

Definition at line 320 of file field_conversion.hpp.

serialize_to_fields()

template<typename Field >

template<typename T >

static std::vector< fr > bb::stdlib::StdlibCodec< Field >::serialize_to_fields ( const T &  val )

inlinestatic

Core stdlib Transcript serialization method.

Serializes an object into a flat vector of in-circuit fr, i.e. field_t elements. This is the inverse of deserialize_from_fields (up to the conventional point-at-infinity representation; see TODO below).

Serializes the following types:

• field_t — no conversion needed; output a single fr.
• bigfield (bb::stdlib::bigfield< Builder, T >) — output 2 fr limbs obtained from the bigfield’s binary-basis limbs recombined according to NUM_LIMB_BITS. Specific to UltraCircuitBuilder.
• goblin field element (bb::stdlib::goblin_field< Builder >) — emit 2 fr limbs by exposing the goblin field’s internal limbs (low, high) as-is. Range constraints are enforced in Translator (see Translator Range Constraint relation). Specific to MegaCircuitBuilder.
• bn254 goblin point (bb::stdlib::element_goblin::goblin_element< Builder_, Fq, Fr, NativeGroup >) — serialize the pair of coordinates (x, y) by concatenating the encodings of each coordinate in the base field (goblin/bigfield form). Point-at-infinity is represented as (0, 0); ECCVM validates this. Specific to MegaCircuitBuilder.
• bn254 point (bb::stdlib::element_default::element< Builder_, Fq, Fr, NativeGroup >) — serialize (x, y) by concatenating the encodings of the two bigfield coordinates. Specific to UltraCircuitBuilder.
• Grumpkin point — serialize (x, y) in the base field fr by concatenating their encodings. The point-at-infinity flag is re-derived from coordinates during deserialization. Specific to UltraCircuitBuilder.
• bb::Univariate<FF, N> or std::array<FF, N> of any of the above — serialize element-wise and concatenate.

Round-trip note:

• For supported types, serialize_to_fields(val) followed by deserialize_from_fields<T>(...) reconstructs an equivalent in-circuit object, assuming the same arithmetization and that range/ECC checks are enforced where applicable during reconstruction (see ECCVM Transcript relation).

TODO(https://github.com/AztecProtocol/barretenberg/issues/1527): make the point-at-infinity representation fully uniform across (de)serialization paths.

Template Parameters

Builder	UltraCircuitBuilder or MegaCircuitBuilder
T	Target object type

Parameters

val	Value to serialize

Returns

Flat vector of fr<Builder> elements

Definition at line 252 of file field_conversion.hpp.

split_challenge()

template<typename Field >

static std::array< fr, 2 > bb::stdlib::StdlibCodec< Field >::split_challenge ( const fr &  challenge )

inlinestatic

Split a challenge field element into two equal-width challenges.

Both lo and hi are 127 bits each (254/2) which provides significantly more than our security parameter bound: 100 bits. The decomposition is constrained to be unique.

Parameters

challenge

Returns

std::array<DataType, 2>

Definition at line 301 of file field_conversion.hpp.

---

The documentation for this class was generated from the following file:

• src/barretenberg/stdlib/primitives/field/field_conversion.hpp