Rails - Jul 2006 - [Newbie] The pickaxe book and benchmark

Hello,

    I was reading the pickaxe book and then I arrived to the chapter 
"When trouble strikes" in the Benchmark section.

I have this code:

#!/usr/bin/ruby -w
require ''benchmark''
include Benchmark

LOOP_COUNT = 1_000_000

bm(12) do |test|
   test.report("normal:") do
     LOOP_COUNT.times do |x|
       y = x +1
     end
   end
   test.report("predefine:") do
     x = y = 0
     LOOP_COUNT.times do |x|
       y = x + 1
     end
   end
end

The "predefine" test is more fast than the "normal". Why?
The only difference that I see is x = y = 0  but I don''t understand

thanks!


                                   Rafael G.

Rafa G. wrote:
> Hello,
>
>    I was reading the pickaxe book and then I arrived to the chapter 
> "When trouble strikes" in the Benchmark section.
>
> I have this code:
>
> #!/usr/bin/ruby -w
> require ''benchmark''
> include Benchmark
>
> LOOP_COUNT = 1_000_000
>
> bm(12) do |test|
>   test.report("normal:") do
>     LOOP_COUNT.times do |x|
>       y = x +1
>     end
>   end
>   test.report("predefine:") do
>     x = y = 0
>     LOOP_COUNT.times do |x|
>       y = x + 1
>     end
>   end
> end
>
> The "predefine" test is more fast than the "normal".
Why?
> The only difference that I see is x = y = 0  but I don''t
understand
>
> thanks!
Because of scope. In the second test, x and y are defined in the scope 
outside the code block, and the block uses the outside variables. In the 
first block, the variables are created for each iteration of the loop.
>
>
>                                   Rafael G.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Thanks!

Inge J?rgensen escribi?:
> Rafa G. wrote:
>> Hello,
>>
>>    I was reading the pickaxe book and then I arrived to the chapter 
>> "When trouble strikes" in the Benchmark section.
>>
>> I have this code:
>>
>> #!/usr/bin/ruby -w
>> require ''benchmark''
>> include Benchmark
>>
>> LOOP_COUNT = 1_000_000
>>
>> bm(12) do |test|
>>   test.report("normal:") do
>>     LOOP_COUNT.times do |x|
>>       y = x +1
>>     end
>>   end
>>   test.report("predefine:") do
>>     x = y = 0
>>     LOOP_COUNT.times do |x|
>>       y = x + 1
>>     end
>>   end
>> end
>>
>> The "predefine" test is more fast than the
"normal". Why?
>> The only difference that I see is x = y = 0  but I don''t
understand
>>
>> thanks!
> Because of scope. In the second test, x and y are defined in the scope 
> outside the code block, and the block uses the outside variables. In the 
> first block, the variables are created for each iteration of the loop.
> 
>>
>>
>>                                   Rafael G.
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
> 
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails