Richard O'Keefe wrote:
Rough guesses:
integer adds, subtracts, and compares are fast,
integer multiplies and divides are much slower,
slow enough that compilers go to some trouble to
do something else when multiplying or dividing
by a constant.
Typically, these days (for both int and fp)...
Multiply is somewhat slower than addition (1x~4x). Many compilers will
go through efforts to convert multiplications into additions, shifts,
etc, but that code is mostly legacy from when multiplication was in the
8x~12x range.
Division is much slower than multiplication (10x~40x). Many compilers
will do all they can to convert these into simpler operations whenever
possible. When in doubt, performance programmers tend to do the same.
Logarithms/exponentiation are also much, much slower than
multiplication. I'm not aware of any compilers that try to optimize
these in any meaningful way. (Though for a very particular task, see the
logfloat package
<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/logfloat>.)
--
Live well,
~wren
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