Commits on Mar 18, 2022

1. secp256k1: Reduce scalar base mult copies. …

   Profiling shows that around 7.5% of the time in scalar base
   multiplication is attributed to duffcopy.  Upon further examination,
   this is the result of a combination of the range statement making copies
   of the bytes and the need to construct a Jacobian point from the
   individual field values stored in the in-memory byte points table.
   
   This optimizes the function to avoid that as follows:
   
   - Perform the conversion to Jacobian once when the affine byte table is
     decompressed from the stored values
   - Make use of those Jacobian points directly
   - Use an indexed for loop instead of a range over the bytes
   - Perform the calculation using the result variable directly instead of
     via a local variable that is copied to the result
   
   The following benchmark results show the speedup is in line with the
   expected gains per the profiling results:
   
   name                     old time/op   new time/op    delta
   ------------------------------------------------------------------------------
   ScalarBaseMultNonConst   24.1µs ±22%   22.5µs ± 2%   -6.97%  (p=0.000 n=98+96)

   

   davecgh committed Mar 18, 2022
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