On 01/19/2014 10:45 PM, Sven Barth wrote:
On 19.01.2014 20:47, Ched wrote:
Dear Freepascalers,
The multiplication in floating arthmetic units is usualy know as being
slower than the addition. So, have I interest to code X+X, 2*X or X*2
when using reals (mainly double and extended) ?And with integers ?
Can't really comment on floats, but for integers the fasted to
multiply by 2 should be a shift left.
Can the compiler optimise this operation choosing the fastest one -
probably depending on the architecture x86, arm, aso.
It can if someone codes support for it (maybe some code generators
already have such simplifications). I thought I've at least seen such
code for integers (that exactly converts *2 to a shl), but I can't
find it currently...
Integer multiplication by a power of 2 constant is converted to a SHL in
pass 1, see nadd.pas:2869.
Nikolay
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
