[flac-dev] "keep qlp coeff precision such that only 32-bit math is required"

[lvqcl]

Martijn van Beurden wrote:

> Op 22-04-15 om 22:45 schreef lvqcl:
>> Currently evaluate_lpc_subframe_() automatically adjusts
>> qlp_coeff_precision when a user sets non-standard order value
>> (via -l option). I don't think that it's incorrect behavior.
>> Why not?
>
> Because what is the point in setting a non-standard value if it
> not used anyway?


I think that the comment in the code ("try to keep qlp coeff precision
such that only 32-bit math is required for decode of <=16bps streams") explains it:
flac overrides the value of qlp_coeff_precision in order to increase decoding speed.
64-bit additions, multiplications and shifts are relatively slow on 32-bit CPUs,
and 32-bit operations are preferable.