Entropy clustering merges symbol histograms to reduce the overall
entropy. The cost of 2 added histograms is compared to the 2 costs
of the individual histograms and if it is smaller, a merge is done.
Except for some symbols (distance and length), the computed cost is
the real final cost based on the histogram, and some constant cost
(independent from the probabilities of the symbols and hence the
merge) because the symbol is encode as Golomb.
This constant cost is useless and can be removed.
Change-Id: I6271e8c0e4111cdeff544cbdb7dec3c67be5309c
histogram_symbols is converted to uint32_t and <<8 into
histogram_argb.
Using a uint32_t buffer from the start prevents copying and
converting the data.
Change-Id: I245003a6a0f048c31519afa25a600d4479e762e3
In practice, this can never happen because:
- 'streak' is at most as long as a histogram
- 'count' counts the number of streaks
'streak' and 'count' are therefore at most as big as the histogram
length which is at most the max of VP8LHistogramNumCodes,
which is 256+24+(1<<10).
Change-Id: I31c8834543479c8a9260732313ea26b045519515
The histograms count the occurrences of len/dist in entropy images.
Those (at most (1<<14) by (1<<14)) are sub-sampled by at least
MIN_HUFFMAN_BITS == 2, hence at most 24 bits in a histogram value.
At most, we multiply by 19 (because the longest histogram is of
size 40 and we do 40>>1, cf code) for the bit cost. So it all fits
in 32 bits.
Change-Id: Ife24b035f54794851ff31f2fac07901f724c6d7f
1 space is most common in the source; this fixes some mixed cases within
lossless files, likely from clang-format
Change-Id: I504206d5bf418781d4131ee73570ecee4e0a69a1
A WebPPicture instance is necessary to call WebPReportProgress() which
sets WebPPicture::error_code so as well use WebPEncodingSetError() to
record errors too, instead of functions returning a WebPEncodingError.
However there must be one WebPPicture instance per thread, with error
codes merged at sync time. A mutex could simplify that but it is not
the objective of this change.
https://groups.google.com/a/webmproject.org/g/webp-discuss/c/yOiP8APubgc/m/vCTvxl6ODgAJ
Change-Id: Ia1a8f9d1199202e1c88484ce719b0180a80447ce
Fix another pessimization found by the pingo image compressor.
Refactoring is necessary to make LZ77 computation
common to cache or no-cache analysis.
Slower by 1.7x instead of 2x
Change-Id: I396701ea6e88543dbfe9471eb552877f6c8ce1e3
previously if the mappings allocation failed histo_queue->queue would be
uninitialized; split the conditionals
Change-Id: I1b50b987e734393893dc8a83a3f314522ccd0c83
The old code simply did not make sense.
The effect is that the pair would be popped from the
queue no matter what; as the queue is small, it does
not matter that much on the results.
But it will matter for a later CL.
Change-Id: If50c9fa9d7f3ac3c48bb7336d81479287d4944c4
When histograms are empty, it is easy to add them.
They should also not be considered when merging histograms
(it is a waste of CPU).
This does not change the compression performance,
just the speed.
Change-Id: I42c721ca0f9c5ea067e73b792aa3db6d5e71d01f
As backward references use the plane code when checking the cost
of a distance, statistics used to compute the cost should use it too.
This provides a small compression improvement at no speed cost.
Change-Id: Icade150929ee39ef6dc0d8b1fc85973086ecf41d
Between each iteration we keep track of the previously found
potential merge hence less work to do.
Change-Id: I2b6237447e79443516a6111727d96c24f10bd98a
It was a bad implementation of a Lehmer random number generator
(the saturation was done wrong and mostly & was used instead of % .....).
That lead to "for" loop stuck with the same values given a specific seed,
hence wasted "for" loops (e.g. seed getting at 374988608 and modulo of 64
later leads to 0 even when updating the seed with the old formula).
As the "for" loops now always return a proper pair of histograms, their
number can greatly be reduced, hence a speedup.
Change-Id: I9f5b44d66cc96fd4824189d92276c3756c8ead5b
Previously, the stochastic method for histogram
combination could finish in a greedy way
if the number of iterations to perform so was smaller.
Except that another greedy combination was performed
afterwards ... hence wasted CPU in some cases.
Change-Id: Ic0f26873e6dc746679486b91cb35d73efee91931
this avoids duplicates between these trees and dsp/, e.g., enc/tree.c,
dec/tree.c, making pulling the whole library source tree into one target
possible
BUG=webp:279
Change-Id: I060a614833c7c24ddd37bf641702ae6a5eef1775
