swift15: BF16 absmax bits belong in the HIGH half of the float32

scripts/verify-swift15-ple.py

@@ -57,9 +57,9 @@ for fname, keys in sorted(shards.items()):
                 gfile = k
         mm.close()
 
-# rebuild the BF16 value from the sign-cleared uint16 bit pattern
-absmax = np.frombuffer(np.uint16(gmax).tobytes() + b"\x00\x00",
-                       dtype=np.float32)[0]
+# rebuild the BF16 value: the 16 bits are the HIGH half of the float32
+absmax = np.frombuffer(b"\x00\x00" + np.uint16(gmax).tobytes(),
+                        dtype=np.float32)[0]
 cap = FP8_E4M3_MAX * SCALE
 print(f"absmax        = {absmax!r}  (tensor: {gfile})")
 print(f"2^log2        = 2^{math.log2(absmax):.3f}")