comment explaining the reason for use of Taus88

fastRandom.cc

@@ -13,6 +13,14 @@ namespace Alepha::Hydrogen  ::detail::  fastRandom_m
 		struct FastRandomState
 		{
 			boost::random::taus88 fastRandomState{ std::random_device{}() };
+			/* The choice of Taus88 is deliberate.  The more familiar Mt19937
+			   is only slightly slower and its cousin Mt11213b is effectively
+			   no slower, but they require 100x to 200x as many integers to
+			   maintain state.  Thus with even only one random variable, the
+			   latter two will exceed cache line size and create cache load,
+			   but with several/many the cache pressure will be significant and
+			   affect performance not just for this code but for the system.
+			*/
 			std::uint32_t pool;
 			int remainingBits= 0;