Update audio primitives for floating point conversion speed

Floats now round-half-up instead of round-half-to-even.
This returns 25% gain in performance for slightly worse rounding.

Also a cosmetic change to convert an if to an add with boolean.

Bug: 69479669
Test: primitives_tests
Change-Id: I15dc17f5732e41594c23831622d0c1642881a711
2 files changed