nx_flac_gate.nx

nx_flac_gate.nx -- proves the FLAC decoder core. Two of these tests guard defects that produce NO error and NO crash: T1 zigzag unfolding -- invert it and every residual has the right magnitude and the wrong sign. Output is noise, nothing reports it. T8 mid/side low-bit -- the encoder drops the low bit of mid and hides it in the low bit of side. Forget to re-insert it and every odd-summed sample pair is off by one: inaudible, invisible on a spectrum, and fatal to the word 'lossless'. T8 uses an ODD sum specifically. NON-VACUITY: T14/T15 are negative controls -- a non-FLAC magic, an over-order fixed predictor and a zero-order LPC must each be REFUSED. license_tier: ORIGINAL