Merge pull request #135 from flyingrobots/F32Scalars/subnormals

feat: Flush subnormals in F32Scalar

Author: flyingrobots

crates/rmg-core/src/math/scalar.rs

@@ -136,6 +136,10 @@ impl F32Scalar {
             Self {
                 value: f32::from_bits(0x7fc0_0000),
             }
+        } else if num.is_subnormal() {
+            Self {
+                value: f32::from_bits(0),
+            }
         } else {
             // Canonicalize -0.0 to +0.0
             Self { value: num + 0.0 }

crates/rmg-core/tests/determinism_policy_tests.rs

@@ -48,7 +48,6 @@ fn test_policy_nan_canonicalization() {
     );
 }
 
-/*
 #[test]
 fn test_policy_subnormal_flushing() {
     // Smallest positive subnormal: 1 bit set in mantissa, 0 exponent
@@ -60,15 +59,41 @@ fn test_policy_subnormal_flushing() {
     let s2 = F32Scalar::new(large_sub);
 
     // Must be flushed to positive zero
-    assert_eq!(s1.to_f32().to_bits(), 0, "Small subnormal not flushed to +0.0");
-    assert_eq!(s2.to_f32().to_bits(), 0, "Large subnormal not flushed to +0.0");
+    assert_eq!(
+        s1.to_f32().to_bits(),
+        0,
+        "Small subnormal not flushed to +0.0"
+    );
+    assert_eq!(
+        s2.to_f32().to_bits(),
+        0,
+        "Large subnormal not flushed to +0.0"
+    );
+    assert_eq!(
+        s1.to_f32().to_bits(),
+        F32Scalar::ZERO.to_f32().to_bits(),
+        "Small subnormal is not equal to ZERO"
+    );
+    assert_eq!(
+        s2.to_f32().to_bits(),
+        F32Scalar::ZERO.to_f32().to_bits(),
+        "Large subnormal is not equal to ZERO"
+    );
 
     // Verify negative subnormals go to +0.0 too (since -0.0 -> +0.0)
     let neg_sub = f32::from_bits(0x80000001);
     let s3 = F32Scalar::new(neg_sub);
-    assert_eq!(s3.to_f32().to_bits(), 0, "Negative subnormal not flushed to +0.0");
+    assert_eq!(
+        s3.to_f32().to_bits(),
+        0,
+        "Negative subnormal not flushed to +0.0"
+    );
+    assert_eq!(
+        s3.to_f32().to_bits(),
+        F32Scalar::ZERO.to_f32().to_bits(),
+        "Negative subnormal is not equal to ZERO"
+    );
 }
-*/
 
 #[test]
 #[cfg(feature = "serde")]

docs/decision-log.md

@@ -7,6 +7,7 @@
 | Date | Context | Decision | Rationale | Consequence |
 | ---- | ------- | -------- | --------- | ----------- |
 | 2025-11-29 | LICENSE | Add SPDX headers to all files | LEGAL PROTECTION 🛡️✨ |
+| 2025-11-30 | `F32Scalar` | Canonicalize subnormal values to zero | Now, they're zero. |
 | 2025-12-01 | `Cargo.toml` bench profile | Remove `panic = "abort"` from `[profile.bench]`. | Silence cargo warning as this setting is ignored for bench profiles; rely on release profile inheritance or default behavior. | Cleaner build output; no behavior change for benches (which default to unwind or abort based on target/inheritance). |
 | 2025-11-30 | `F32Scalar` NaN reflexivity | Update `PartialEq` implementation to use `total_cmp` (via `Ord`) instead of `f32::eq`. | Ensures `Eq` reflexivity holds even for NaN (`NaN == NaN`), consistent with `Ord`. Prevents violations of the `Eq` contract in collections. | `F32Scalar` now behaves as a totally ordered type; NaN values are considered equal to themselves and comparable. |
 | 2025-11-30 | `F32Scalar` NaN canonicalization | Canonicalize all NaNs to `0x7fc00000` in `F32Scalar::new`. Update MSRV to 1.83.0 for `const` `is_nan`/`from_bits`. | Guarantees bit-level determinism for all float values including error states. Unifies representation across platforms. MSRV bump enables safe, readable `const` implementation. | All NaNs are now bitwise identical; `const fn` constructors remain available; `rmg-core` requires Rust 1.83.0+. |

docs/execution-plan.md

@@ -42,6 +42,12 @@ This is Codex’s working map for building Echo. Update it relentlessly—each s
 - Changes: Removed `panic = "abort"` from `[profile.bench]`.
 - Status: Completed; warning no longer appears.
 
+> 2025-11-30 – Handle subnormal f32 values in F32Scalar
+
+- Goal: Canonicalize subnormal f32 values to zero.
+- Scope: subnormals, F32Scalars.
+- Plan: Make 'em zero.
+
 > 2025-12-01 — Fix “How Echo Works” LaTeX build (non-interactive PDF)
 
 - Goal: unblock `docs/guides/how-do-echo-work` PDF generation without interactive TeX prompts.