pstef 38ba87f359 Test: pin the multiplier deficit in the upper binade ...

The Booth predicate is keyed to fixed bit positions of ft, but the
truncation column moves one bit between the binades -- and every
zero-tail row I measured sat in the lower binade, at fs = 2^23. So the
region where the decrement fires with the product in the upper binade
had never been observed on silicon. The fpmul3 capture already had it.
The counts and the row provenance are at the tables.

One dead end worth recording, since the data invites it: do not split
this by binade, split it by T. fs = 0xFFFFFF looks like the predicate
carries no information there (0.1907% low with Booth on, 0.1976% with it
off), but it has exactly one T == 0 row, so that is measuring the
unmodelled 0 < tail < deficit class instead. At fs = 0x800001, lower
binade and also almost entirely that class, Booth is strictly necessary:
13,248/13,248 on, 0/262,144 off.

2026-08-04 21:13:34 +02:00

..

ctest

Test: pin the multiplier deficit in the upper binade

2026-08-04 21:13:34 +02:00

run_test.pl

misc: A couple of more leftovers from SPU2 merge.

2021-01-04 02:07:30 +01:00