[Numpy-discussion] where are the benefits of ldexp and/or "array times 2"?
Fri May 22 04:55:31 CDT 2009
> Hi all,
> I expected to have some speedup via using ldexp or multiplying an
> array by a power of 2 (doesn't it have to perform a simple shift of
> mantissa?), but I don't see the one.
> # Let me also note -
> # 1) using b = 2 * ones(N) or b = zeros(N) doesn't yield any speedup
> vs b = rand()
> # 2) using A * 2.0 (or mere 2) instead of 2.1 doesn't yield any
> speedup, despite it is exact integer power of 2.
On recent processors multiplication is very fast and takes 1.5 clock
cycles (float, double precision), independent of the values. There is
very little gain by using bit shift operators.
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