readValue is a hot function, clocking in at ~13% flat CPU use in
CodeDecoder. In particular, looping over the bytes is slow. That's
partially because the code contains a bounds check at the start of the
loop.
The source of the problem is that scanp is a signed integer, and comes
from a field, so the compiler doesn't know that it's non-negative. Help
it with a simple and comparatively cheap hint.
While at it, use scanp as the index variable directly, removing the need
for a duplicate index variable which is later added back into scanp.
name old time/op new time/op delta
CodeDecoder-8 11.3ms ± 1% 11.2ms ± 1% -0.98% (p=0.000 n=9+9)
name old speed new speed delta
CodeDecoder-8 172MB/s ± 1% 174MB/s ± 1% +0.99% (p=0.000 n=9+9)