[Numpy-discussion] Set values of a matrix within a specified range to zero

[Robert Kern]

On Tue, Mar 30, 2010 at 16:35, Ryan May <rmay31 at gmail.com> wrote:
> On Tue, Mar 30, 2010 at 3:16 PM, Friedrich Romstedt
> <friedrichromstedt at gmail.com> wrote:

>> x *= ((x <= 23) | (x >= 45))  .
>
> Interesting. In an ideal world, I'd love to see why exactly that is,
> because I don't think multiplication should be faster than a boolean
> op.

Branch prediction failures are really costly in modern CPUs.

http://en.wikipedia.org/wiki/Branch_prediction

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco