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

2026-10-06 20:39:21 -07:00
parent d062a376b2
commit 3e46d51df8
1 changed files with 3 additions and 3 deletions
@@ -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}")