bb::FrCodec Class Reference

#include <field_conversion.hpp>

Public Types
using	DataType = bb::fr
using	fr = bb::fr
using	fq = grumpkin::fr
using	bn254_commitment = curve::BN254::AffineElement
using	grumpkin_commitment = curve::Grumpkin::AffineElement

Static Public Member Functions
template<typename T >
static constexpr size_t	calc_num_fields ()
template<typename T >
static bool	check_point_at_infinity (std::span< const bb::fr > fr_vec)
	Check whether raw limbs represent the point at infinity (all limbs zero).
static fq	convert_grumpkin_fr_from_bn254_frs (std::span< const bb::fr > fr_vec)
	Converts 2 bb::fr elements to fq.
static std::vector< bb::fr >	convert_grumpkin_fr_to_bn254_frs (const fq &val)
	Converts fq to 2 bb::fr elements (inverse of the above).
template<typename T >
static T	deserialize_from_fields (std::span< const fr > fr_vec)
template<typename T >
static std::vector< fr >	serialize_to_fields (const T &val)
	Conversion from transcript values to bb::frs.
static std::array< bb::fr, 2 >	split_challenge (const bb::fr &challenge)
	Split a challenge field element into two equal-width challenges.
template<typename T >
static T	convert_short_challenge (const bb::fr &challenge)
	Convert a short (≤127-bit limb) challenge to a target type (fr or fq).
template<typename T >
static T	convert_full_challenge (const bb::fr &challenge)
	Convert a full-width challenge to a target type (fr or fq).

Detailed Description

Definition at line 19 of file field_conversion.hpp.

Member Typedef Documentation

bn254_commitment

using bb::FrCodec::bn254_commitment = curve::BN254::AffineElement

Definition at line 24 of file field_conversion.hpp.

DataType

using bb::FrCodec::DataType = bb::fr

Definition at line 21 of file field_conversion.hpp.

fq

using bb::FrCodec::fq = grumpkin::fr

Definition at line 23 of file field_conversion.hpp.

fr

using bb::FrCodec::fr = bb::fr

Definition at line 22 of file field_conversion.hpp.

grumpkin_commitment

using bb::FrCodec::grumpkin_commitment = curve::Grumpkin::AffineElement

Definition at line 25 of file field_conversion.hpp.

Member Function Documentation

calc_num_fields()

template<typename T >

static constexpr size_t bb::FrCodec::calc_num_fields ( )

inlinestaticconstexpr

Definition at line 28 of file field_conversion.hpp.

check_point_at_infinity()

template<typename T >

static bool bb::FrCodec::check_point_at_infinity ( std::span< const bb::fr >  fr_vec )

inlinestatic

Check whether raw limbs represent the point at infinity (all limbs zero).

This matches the circuit behavior in StdlibCodec::check_point_at_infinity. We check raw limbs BEFORE deserializing to field elements to ensure that alias values (e.g., x=modulus, y=modulus) are NOT treated as point at infinity. Only the canonical (0,0) representation with all-zero limbs is accepted.

Definition at line 49 of file field_conversion.hpp.

convert_full_challenge()

template<typename T >

static T bb::FrCodec::convert_full_challenge ( const bb::fr &  challenge )

inlinestatic

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

For fq (a Grumpkin scalar) the conversion is exact and canonical: the BN254 scalar modulus r is smaller than the base modulus q, so every challenge value (< r) is < q and reinterprets directly as an fq element with no reduction. This mirrors the recursive StdlibCodec::convert_full_challenge, which splits the same value into bigfield limbs.

Definition at line 233 of file field_conversion.hpp.

convert_grumpkin_fr_from_bn254_frs()

static fq bb::FrCodec::convert_grumpkin_fr_from_bn254_frs ( std::span< const bb::fr >  fr_vec )

inlinestatic

Converts 2 bb::fr elements to fq.

Splits into 136-bit lower chunk and 118-bit upper chunk to mirror stdlib bigfield limbs (68-bit each). Rejects aliased values (>= fq::modulus) to ensure canonical representation.

Definition at line 65 of file field_conversion.hpp.

convert_grumpkin_fr_to_bn254_frs()

static std::vector< bb::fr > bb::FrCodec::convert_grumpkin_fr_to_bn254_frs ( const fq &  val )

inlinestatic

Converts fq to 2 bb::fr elements (inverse of the above).

Definition at line 90 of file field_conversion.hpp.

convert_short_challenge()

template<typename T >

static T bb::FrCodec::convert_short_challenge ( const bb::fr &  challenge )

inlinestatic

Convert a short (≤127-bit limb) challenge to a target type (fr or fq).

Input is a single 127-bit limb produced by split_challenge. For fq (a Grumpkin scalar) the value must fit in the lower two simulated bigfield limbs, which is what the short width guarantees.

Definition at line 214 of file field_conversion.hpp.

deserialize_from_fields()

template<typename T >

static T bb::FrCodec::deserialize_from_fields ( std::span< const fr >  fr_vec )

inlinestatic

Definition at line 112 of file field_conversion.hpp.

serialize_to_fields()

template<typename T >

static std::vector< fr > bb::FrCodec::serialize_to_fields ( const T &  val )

inlinestatic

Conversion from transcript values to bb::frs.

Definition at line 156 of file field_conversion.hpp.

split_challenge()

static std::array< bb::fr, 2 > bb::FrCodec::split_challenge ( const bb::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<bb::fr, 2>

Definition at line 196 of file field_conversion.hpp.

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

• src/barretenberg/ecc/fields/field_conversion.hpp