series 4 codec work, inital decode success

analysis_idf/idfh_period.py

@@ -0,0 +1,41 @@
+"""Find IDFH interval period via auto-correlation of structural patterns."""
+from __future__ import annotations
+import sys
+from pathlib import Path
+from collections import Counter
+
+REPO = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(REPO))
+
+
+def main():
+    target = REPO / "tests/fixtures/THORDATA_example/THORDATA_example/UPMC Presby/UM13981/UM13981_20220805075441.IDFH"
+    buf = target.read_bytes()
+    body_start = 0xF96
+    body_end   = 0x270C
+    body = buf[body_start:body_end]
+    print(f"body size: {len(body)} bytes (file {len(buf)} bytes)")
+
+    # For each candidate interval size, count how many bytes at fixed offsets within
+    # each interval are zero (consistent column-zero pattern indicates correct size).
+    print()
+    print("=== zero-column score by interval size (higher = more likely) ===")
+    best = []
+    for sz in range(16, 100):
+        n = len(body) // sz
+        if n < 30:
+            continue
+        # For each column position within an interval, count how many of n intervals have zero
+        score = 0
+        for col in range(sz):
+            zeros = sum(1 for i in range(n) if body[i*sz + col] == 0)
+            if zeros >= n * 0.9:
+                score += 1
+        best.append((score, sz, n))
+    best.sort(reverse=True)
+    for score, sz, n in best[:10]:
+        print(f"  size={sz:3d}  n_intervals={n}  consistently-zero-cols={score}")
+
+
+if __name__ == "__main__":
+    main()