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This works via a lookup table and is mostly implemented in a new module fastexp.c. No perceptible differences in the output can be seen. The speed increase is not huge, maybe a couple of minutes.
The arrays EXP_TABLE_* need to be defined in order for the tasks to compile, even if they are not filled or accessed. Therefore I added a nominal definition in this case. I also added a couple of comment lines to fastexp.c.
smaret
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Jun 26, 2015
Implement a fast exponential function to speed up the code
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This includes a Makefile option to use a lookup-table replacement for the exponential function, which however (due to cunning use of the properties of the function) returns a value with full floating-point precision, indeed with better precision than that for much of the range. Use of this option reduces the run time by 25%.