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MSM/Serialization: implement third constraint #1892

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Mar 5, 2024
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MSM/Serialization: implement third constraint #1892

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60 changes: 48 additions & 12 deletions msm/src/serialization/witness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -142,16 +142,20 @@ pub fn deserialize_field_element<Fp: Field, Env: InterpreterEnv<Fp>>(
let limb1_var = env.copy(&input_limb1, kimchi_limbs1);
let limb2_var = env.copy(&input_limb2, kimchi_limbs2);

let mut limb2_vars = vec![];
let limb2_0_var = {
let limb2_0 = Env::get_column_for_intermediate_limb(0);
env.bitmask_be(&input_limb2, 4, 0, limb2_0)
let limb2_0_var = env.bitmask_be(&input_limb2, 4, 0, limb2_0);
limb2_vars.push(limb2_0_var.clone());
limb2_0_var
};
// Compute individual 4 bits limbs of b2
{
let mut constraint = limb2_var.clone() - limb2_0_var.clone();
let mut constraint = limb2_var.clone() - limb2_vars[0].clone();
for j in 1..N_INTERMEDIATE_LIMBS {
let position = Env::get_column_for_intermediate_limb(j);
let var = env.bitmask_be(&input_limb2, 4 * (j + 1) as u32, 4 * j as u32, position);
limb2_vars.push(var.clone());
let pow: u128 = 1 << (4 * j);
let pow = Env::constant(pow.into());
constraint = constraint - var * pow;
Expand Down Expand Up @@ -274,17 +278,49 @@ pub fn deserialize_field_element<Fp: Field, Env: InterpreterEnv<Fp>>(

env.add_constraint(constraint);

// -- Start third constraint
// FIXME: range check
let c12 = Env::get_column_for_msm_limb(12);
let c13 = Env::get_column_for_msm_limb(13);
let c14 = Env::get_column_for_msm_limb(14);
let c15 = Env::get_column_for_msm_limb(15);
let c16 = Env::get_column_for_msm_limb(16);
env.bitmask_be(&input_limb2, 19, 4, c12);
env.bitmask_be(&input_limb2, 34, 19, c13);
env.bitmask_be(&input_limb2, 49, 34, c14);
env.bitmask_be(&input_limb2, 64, 49, c15);
env.bitmask_be(&input_limb2, 79, 64, c16);
let c12_var = {
let c12 = Env::get_column_for_msm_limb(12);
env.bitmask_be(&input_limb2, 19, 4, c12)
};
let c13_var = {
let c13 = Env::get_column_for_msm_limb(13);
env.bitmask_be(&input_limb2, 34, 19, c13)
};

let c14_var = {
let c14 = Env::get_column_for_msm_limb(14);
env.bitmask_be(&input_limb2, 49, 34, c14)
};

let c15_var = {
let c15 = Env::get_column_for_msm_limb(15);
env.bitmask_be(&input_limb2, 64, 49, c15)
};
let c16_var = {
let c16 = Env::get_column_for_msm_limb(16);
env.bitmask_be(&input_limb2, 79, 64, c16)
};

// Unfolding for readability.
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let shl_15 = Fp::from(1u128 << 15u128);
let mut cst = Env::constant(shl_15);
let mut constraint = c12_var;

constraint = constraint + c13_var * cst.clone();
cst = cst * Env::constant(shl_15);
constraint = constraint + c14_var * cst.clone();
cst = cst * Env::constant(shl_15);
constraint = constraint + c15_var * cst.clone();
cst = cst * Env::constant(shl_15);
constraint = constraint + c16_var * cst.clone();

constraint = (1..20).fold(constraint, |constraint, i| {
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let var = limb2_vars[i].clone() * Env::constant(Fp::from(1u128 << (4 * (i - 1))));
constraint - var
});
env.add_constraint(constraint);
}

#[cfg(test)]
Expand Down