SoA implementation for float and AVX2 includind the polyexp fix

Makefile

@@ -108,13 +108,20 @@ BENCH_ITER ?= 1000
 # Verification parameters
 
 ifneq ($(filter float_%,$(VARIANT)),)
-REFERENCE_CSV ?= reference/baseline_float_n60_i4000.csv
+# Float verify uses a short horizon (500 iters). The simulation is chaotic - a 1-ULP perturbation
+# amplifies by ~exp(t/200) - so floats can't hold bit-equality across variants over 4000 iters
+# no matter what we do (different layouts -> different FMA placements -> 1-ULP drift -> meters by t=4000).
+# At 500 iters the amplifier is still small: AVX2 variants drift max ~4mm vs the scalar reference,
+# well under 1cm, and real bugs still show as O(m) errors. 4000 iters drifts to meters even when
+# the variant is correct, so that horizon is useless for verify.
+REFERENCE_N_ITER ?= 500
+REFERENCE_CSV ?= reference/baseline_float_n60_i500.csv
 else
+REFERENCE_N_ITER ?= 4000
 REFERENCE_CSV ?= reference/baseline_n60_i4000.csv
 endif
 
 REFERENCE_N_P ?= 60
-REFERENCE_N_ITER ?= 4000
 VERIFY_CSV := verify_$(VARIANT).csv
 
 .PHONY: all main run bench run-bench bench-suite video asm test clean clean-all verify
@@ -194,4 +201,4 @@ clean:
 # WARNING: this deletes all *.csv and *.mp4 files in this directory.
 # Move any output files you want to keep to another directory before running it.
 clean-all: clean
-	rm -f *.csv *.mp4
+	rm -f *.csv *.mp4