Change the bit-stream (without causing desync)

Got authorization from all copyright holders

This was computing on uninitialized data (though the result was never
used)

This provides more entropy and allows some more flexibility on the
encoder side.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

Jean-Marc's original anti-collapse patch used a threshold on the
 content of a decoded band to determine whether or not it should
 be filled with random noise.
Since this is highly sensitive to the accuracy of the
 implementation, it could lead to significant decoder output
 differences even if decoding error up to that point was relatively
 small.

This patch detects collapsed bands from the output of the vector
 quantizer, using exact integer arithmetic.
It makes two simplifying assumptions:
 a) If either input to haar1() is non-zero during TF resolution
     adjustments, then the output will be non-zero.
 b) If the content of a block is non-zero in any of the bands that
     are used for folding, then the folded output will be non-zero.
b) in particular is likely to be false when SPREAD_NONE is used.
It also ignores the case where mid and side are orthogonal in
 stereo_merge, but this is relatively unlikely.
This misses just over 3% of the cases that Jean-Marc's anti-collapse
 detection strategy would catch, but does not mis-classify any (all
 detected collapses are true collapses).

This patch overloads the "fill" parameter to mark which blocks have
 non-zero content for folding.
As a consequence, if a set of blocks on one side of a split has
 collapsed, _no_ folding is done: the result would be zero anyway,
 except for short blocks with SPREAD_AGGRESSIVE that are split down
 to a single block, but a) that means a lot of bits were available
 so a collapse is unlikely and b) anti-collapse can fill the block
 anyway, if it's used.
This also means that if itheta==0 or itheta==16384, we no longer
 fold at all on that side (even with long blocks), since we'd be
 multiplying the result by zero anyway.

These were stored internally in one order and in the bitstream in a
 different order.
Both used bare constants, making it unclear what either actually
 meant.
This changes them to use the same order, gives them named constants,
 and renames all the "fold" decision stuff to "spread" instead,
 since that is what it is really controlling.

There's no explicit signaling for it yet.

Decision not yet implemented in the encoder

Folding now moved to alg_quant() and alg_unquant(). No more funny short block
alignment checks because bands now have to be aligned.

scheme. Keeping Hadamard as an option (disabled for now) for transients.

Changed compute_allocation_table() so it handles ebands that start and end in the same allocation band. Also fixed a minor C89 issue.

transient spreading.

Timothy Terriberry authored 15 years ago and Jean-Marc Valin committed 15 years ago

Expose the normalized range for reciprocal square roots in fixed-point mode. This allows subsequnt calculations to use the full precision of the result.