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refactor(cast): unify downcast felt252 canonicalization branches #1653

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Merged
TomerStarkware merged 1 commit into from
Aug 12, 2026
Merged

refactor(cast): unify downcast felt252 canonicalization branches #1653

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40 changes: 21 additions & 19 deletions src/libfuncs/cast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ use melior::{
ir::{r#type::IntegerType, Block, Location, Value, ValueLike},
Context,
};
use num_bigint::{BigInt, Sign};
use num_bigint::{BigInt, BigUint, Sign};
use num_traits::One;

/// Select and call the correct libfunc builder function from the selector.
Expand Down Expand Up @@ -145,26 +145,28 @@ pub fn build_downcast<'ctx, 'this>(
// 2. if it is a bounded_int, we need to offset the value to get the
// actual value.
let src_value = if is_signed && src_ty.is_felt252(registry)? {
if src_range.upper.is_one() {
let adj_offset =
entry.const_int_from_type(context, location, PRIME.clone(), src_value.r#type())?;
entry.append_op_result(arith::subi(src_value, adj_offset, location))?
} else {
let adj_offset = entry.const_int_from_type(
context,
location,
HALF_PRIME.clone(),
src_value.r#type(),
)?;
let is_negative =
entry.cmpi(context, CmpiPredicate::Ugt, src_value, adj_offset, location)?;
// A felt is interpreted as negative (`felt - PRIME`) when it exceeds
// a threshold: HALF_PRIME when the destination range straddles zero,
// and 0 when it is non-positive (every nonzero felt is negative,
// while felt 0 stays 0 and must fail the bounds check).
let adj_offset = entry.const_int_from_type(
context,
location,
if src_range.upper.is_one() {
BigUint::ZERO
} else {
HALF_PRIME.clone()
},
src_value.r#type(),
)?;
let is_negative =
entry.cmpi(context, CmpiPredicate::Ugt, src_value, adj_offset, location)?;

let k_prime =
entry.const_int_from_type(context, location, PRIME.clone(), src_value.r#type())?;
let adj_value = entry.append_op_result(arith::subi(src_value, k_prime, location))?;
let k_prime =
entry.const_int_from_type(context, location, PRIME.clone(), src_value.r#type())?;
let adj_value = entry.append_op_result(arith::subi(src_value, k_prime, location))?;

entry.append_op_result(arith::select(is_negative, adj_value, src_value, location))?
}
entry.append_op_result(arith::select(is_negative, adj_value, src_value, location))?
} else if src_ty.is_bounded_int(registry)? && src_range.lower != BigInt::ZERO {
let dst_offset = entry.const_int_from_type(
context,
Expand Down
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