[Vm-dev] Reed Solomon plugins & performance slow down

Levente Uzonyi leves at caesar.elte.hu
Mon May 31 00:18:34 UTC 2021

Hi Robert,

I had a quick look at the plugin code. The operations you implemented in 
the plugin are way too simple. The VM's JIT makes the smalltalk code run 
faster, because it has the same operations implemented, and it can avoid 
calling the overhead of calling the primitive many times. Hence the 

For example, RSFECPlugin >> #primitiveAddOrSubtractby seems to implement 
bitwise xor on two 32-bit unsigned values, but the arguments are always 
0-255. The VM has primitive 16, which does bitwise xor and covers that 
input range, so the JIT, combined with other operations can generate 
machine code directly with that without jumping back and forth between 
native code and smalltalk.

If you want a plugin to provide any noticable speedup, you need to do 
more computation in a single primtiive call.


P.S.: I think, in RSFECGenericGC >> #initializeExpTable, the lines

 					x := x bitXor: primitive.
 					x bitAnd: (size - 1)]].

should read

 					x := (x bitXor: primitive) bitAnd: size - 1 ]].

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