perf(felt252): compute felt252_div via a runtime binding

[TomerStarkware]

Stacked on #1647 (felt252_mul binding). Review/merge that first; this PR's base is tomer/felt252_mul_pr, so it shows only the division change.

What

Route felt252 division through a runtime binding (cairo_native__felt252_div) instead of lowering it inline as an extended-euclidean modular inverse followed by an i512 multiply-and-remainder.

Why

The inline form has the same hazard the mul binding removed, and then some: it legalizes into huge limb sequences — the i512 remainder being the worst offender — which makes O3 register allocation of division-heavy contracts pathologically slow. It also computed the modular inverse via a large MLIR extended-euclidean loop.

The binding uses starknet-types-core's field_div (optimized Montgomery inverse). rhs originates from a NonZero<felt252>, so it is guaranteed nonzero and from_felt_unchecked is safe. No builtin/range-check accounting is involved (felt division is a pure field op).

Changes

• src/runtime.rs — cairo_native__felt252_div via field_div
• src/metadata/runtime_bindings.rs — Felt252Div binding (symbol, fn-ptr, emitter, setup_runtime); removed the now-dead ExtendedEuclideanWidth::U252, which was constructed only by the old division path (U31/U256/U384 remain, used by egcd / u256-invmod)
• src/libfuncs/felt252.rs — Div routed to the binding; inline euclidean + i512 multiply/remainder removed

All felt252 libfunc tests pass (incl. felt252_div/felt252_div_const: division-by-zero panics, valid quotients, and negative operands).

🤖 Generated with Claude Code

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This change is 

[github-actions]

✅ Code is now correctly formatted.

[orizi]

@orizi made 2 comments.
Reviewable status: 0 of 3 files reviewed, 2 unresolved discussions (waiting on TomerStarkware).

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src/metadata/runtime_bindings.rs line 326 at r1 (raw file):

    /// little-endian felt252 buffers; the result is written to `dst_ptr`.
    #[allow(clippy::too_many_arguments)]
    pub fn felt252_div<'c, 'a>(

put near mul.

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src/metadata/runtime_bindings.rs line 333 at r1 (raw file):

        dst_ptr: Value<'c, '_>,
        lhs_ptr: Value<'c, '_>,
        rhs_ptr: Value<'c, '_>,

and remove the allow.

Suggestion:

        [dst_ptr, lhs_ptr, rhs_ptr]: [Value<'c, '_>; 3],

[orizi]

@orizi made 1 comment.
Reviewable status: 0 of 3 files reviewed, 3 unresolved discussions (waiting on TomerStarkware).

---

-- commits line 1 at r2:
rebase

[orizi]

@orizi made 1 comment.
Reviewable status: 0 of 3 files reviewed, 4 unresolved discussions (waiting on TomerStarkware).

---

src/runtime.rs line 139 at r1 (raw file):

///
/// `rhs` originates from a `NonZero<felt252>`, so it is guaranteed nonzero;
/// `field_div` uses the optimized Montgomery inverse.

move near mul

[TomerStarkware]

@TomerStarkware made 3 comments.
Reviewable status: 0 of 3 files reviewed, 4 unresolved discussions (waiting on orizi).

---

-- commits line 1 at r2:

Previously, orizi wrote…

rebase

Done.

---

src/runtime.rs line 139 at r1 (raw file):

Previously, orizi wrote…

move near mul

Done.

---

src/metadata/runtime_bindings.rs line 333 at r1 (raw file):

Previously, orizi wrote…

and remove the allow.

Done.

[github-actions]

Benchmarking results

Benchmark for program dict_insert

Open benchmarks

Command	Mean [s]	Min [s]	Max [s]	Relative
Cairo-vm (Rust, Cairo 1)	10.312 ± 0.083	10.249	10.536	5.78 ± 0.07
cairo-native (embedded AOT)	1.785 ± 0.017	1.761	1.811	1.00
cairo-native (embedded JIT using LLVM's ORC Engine)	1.788 ± 0.010	1.770	1.803	1.00 ± 0.01

Benchmark for program dict_snapshot

Open benchmarks

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
Cairo-vm (Rust, Cairo 1)	514.0 ± 2.5	508.1	517.3	1.00
cairo-native (embedded AOT)	1600.3 ± 7.1	1592.4	1613.0	3.11 ± 0.02
cairo-native (embedded JIT using LLVM's ORC Engine)	1636.6 ± 6.8	1627.1	1650.4	3.18 ± 0.02

Benchmark for program factorial_2M

Open benchmarks

Command	Mean [s]	Min [s]	Max [s]	Relative
Cairo-vm (Rust, Cairo 1)	4.614 ± 0.034	4.589	4.688	2.76 ± 0.02
cairo-native (embedded AOT)	1.672 ± 0.006	1.663	1.681	1.00
cairo-native (embedded JIT using LLVM's ORC Engine)	1.692 ± 0.010	1.676	1.709	1.01 ± 0.01

Benchmark for program fib_2M

Open benchmarks

Command	Mean [s]	Min [s]	Max [s]	Relative
Cairo-vm (Rust, Cairo 1)	4.524 ± 0.011	4.506	4.543	2.79 ± 0.03
cairo-native (embedded AOT)	1.621 ± 0.017	1.606	1.663	1.00
cairo-native (embedded JIT using LLVM's ORC Engine)	1.655 ± 0.019	1.633	1.707	1.02 ± 0.02

Benchmark for program linear_search

Open benchmarks

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
Cairo-vm (Rust, Cairo 1)	554.6 ± 6.7	547.4	566.3	1.00
cairo-native (embedded AOT)	1631.2 ± 14.2	1611.8	1661.5	2.94 ± 0.04
cairo-native (embedded JIT using LLVM's ORC Engine)	1662.7 ± 8.0	1648.0	1672.1	3.00 ± 0.04

Benchmark for program logistic_map

Open benchmarks

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
Cairo-vm (Rust, Cairo 1)	469.5 ± 2.7	466.5	474.0	1.00
cairo-native (embedded AOT)	1610.4 ± 5.0	1604.7	1617.9	3.43 ± 0.02
cairo-native (embedded JIT using LLVM's ORC Engine)	1645.1 ± 11.5	1631.1	1665.5	3.50 ± 0.03

[github-actions]

Benchmark results Main vs HEAD.

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base dict_insert.cairo (JIT)	1.949 ± 0.024	1.921	1.993	1.01 ± 0.02
base dict_insert.cairo (AOT)	1.925 ± 0.021	1.896	1.958	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head dict_insert.cairo (JIT)	1.683 ± 0.020	1.667	1.736	1.00 ± 0.01
head dict_insert.cairo (AOT)	1.682 ± 0.013	1.667	1.707	1.00

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base dict_snapshot.cairo (JIT)	1.748 ± 0.019	1.723	1.790	1.02 ± 0.02
base dict_snapshot.cairo (AOT)	1.713 ± 0.025	1.683	1.770	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head dict_snapshot.cairo (JIT)	1.525 ± 0.021	1.496	1.557	1.02 ± 0.02
head dict_snapshot.cairo (AOT)	1.488 ± 0.017	1.466	1.529	1.00

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base factorial_2M.cairo (JIT)	1.787 ± 0.022	1.767	1.844	1.02 ± 0.02
base factorial_2M.cairo (AOT)	1.761 ± 0.021	1.735	1.805	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head factorial_2M.cairo (JIT)	1.557 ± 0.014	1.536	1.585	1.01 ± 0.02
head factorial_2M.cairo (AOT)	1.540 ± 0.032	1.512	1.613	1.00

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base fib_2M.cairo (JIT)	1.695 ± 0.016	1.671	1.726	1.03 ± 0.01
base fib_2M.cairo (AOT)	1.646 ± 0.016	1.622	1.670	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head fib_2M.cairo (JIT)	1.508 ± 0.015	1.494	1.542	1.03 ± 0.01
head fib_2M.cairo (AOT)	1.471 ± 0.007	1.464	1.483	1.00

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base linear_search.cairo (JIT)	1.712 ± 0.019	1.689	1.739	1.03 ± 0.01
base linear_search.cairo (AOT)	1.667 ± 0.008	1.656	1.682	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head linear_search.cairo (JIT)	1.523 ± 0.007	1.510	1.532	1.01 ± 0.01
head linear_search.cairo (AOT)	1.506 ± 0.009	1.490	1.519	1.00

Base

Command	Mean [s]	Min [s]	Max [s]	Relative
base logistic_map.cairo (JIT)	1.725 ± 0.025	1.692	1.760	1.03 ± 0.02
base logistic_map.cairo (AOT)	1.677 ± 0.021	1.634	1.705	1.00

Head

Command	Mean [s]	Min [s]	Max [s]	Relative
head logistic_map.cairo (JIT)	1.499 ± 0.009	1.486	1.519	1.02 ± 0.01
head logistic_map.cairo (AOT)	1.470 ± 0.006	1.457	1.475	1.00

[orizi]

@orizi reviewed 3 files and all commit messages, made 1 comment, and resolved 4 discussions.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on TomerStarkware).