----- Original Message ----- From: "Ravi" To: Sent: Wednesday, February 03, 2010 4:52 AM Subject: Re: [Boost-users] PP: 2 to the power x macro

On Monday 01 February 2010 11:56:35 Hicham Mouline wrote:

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I have written this code to return 2 to the power x.

Just a little confused reading your code; does POWER2(6) give you 64? Or are you trying to produce the sequence 1,2,4,8,16,32,64? If the former, why not simply use the left shift operator?

Regards, Ravi

I can't find this left shift operator in Boost.PP. Do you mean << ? But then how do I evaluate it in the context of the preprocessor? regards,

2010/2/4 Ravi

On Tuesday 02 February 2010 21:29:40 Hicham Mouline wrote:

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I can't find this left shift operator in Boost.PP. Do you mean << ? But then how do I evaluate it in the context of the preprocessor?

Unless I have misunderstood your question (very likely), isn't this what you need?

#define POWER2(a) (1<

How about this? // Must expand to "int foo8;", but it does not. int BOOST_PP_CAT(foo, POWER2(3)); Roman Perepelitsa.

2010/2/4 Hicham Mouline

So Roman, what do you think of my POWER2 implementation?

It is very slow (to preprocess) in an actual example I have. Can anyone see a faster implementation?

I'd use something like this: #define POWER_2_0 1 #define POWER_2_1 2 #define POWER_2_2 4 #define POWER_2_3 8 #define POWER_2_4 16 #define POWER_2_5 32 #define POWER_2_6 64 #define POWER_2_7 128 #define POWER_2_8 256 #define POWER_2(n) BOOST_PP_CAT(POWER_2_, n) It's obviously fast and obviously correct. Roman Perepelitsa.