Commits on Mar 14, 2023

1. Changed stream list to arrays and optimized stream lookup with SSE2. …

   The stream list in the SRTP context is now implemented with two arrays:
   an array of SSRCs and an array of pointers to the streams corresponding
   to the SSRCs. The streams no longer form a linked list.
   
   Stream lookup by SSRC is now performed over the array of SSRCs, which
   is considerably faster because it is more cache-friendly. Additionally,
   the lookup is optimized for SSE2, which provides an additional massive
   speedup with many streams in the list. Although the lookup still has
   linear complexity, its absolute times are reduced and with tens to
   hundreds elements are lower or comparable with a typical rb-tree
   equivalent.
   
   Expected speedup of SSE2 version over the previous implementation:
   
   SSRCs    speedup (scalar)   speedup (SSE2)
   
   1        0.39x              0.22x
   3        0.57x              0.23x
   5        0.69x              0.62x
   10       0.77x              1.43x
   20       0.86x              2.38x
   30       0.87x              3.44x
   50       1.13x              6.21x
   100      1.25x              8.51x
   200      1.30x              9.83x
   
   These numbers were obtained on a Core i7 2600K.
   
   At small numbers of SSRCs the new algorithm is somewhat slower, but
   given that the absolute and relative times of the lookup are very small,
   that slowdown is not very significant.

   

   Lastique committed Mar 14, 2023
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