Dr J R Stockton wrote:
> In comp.lang.pascal.ansi-iso message <f7OdnZKR3sNIXPfaRVnyuQA@[EMAIL PROTECTED]
>,
> Thu, 20 Dec 2007 19:29:28, Richard Heathfield <rjh@[EMAIL PROTECTED]
>
> posted:
>> john said:
>>
>>> Hi, regarding Turbo Pascal 7.x (or the standard), is there any power
>>> function provided?
>>>
>>> Something like
>>>
>>> power(10,4) meaning 10 ^4, or something similar.
>>
>> Pascal offers EXP and LN. N^P = EXP(P * LN(N)).
>>
>> Thus, 10^4 = EXP(4 * LN(10)).
>
> The original example was an integer example, and you have given a float
> method. I'm almost sure that your code will almost always give a float
> of exact integer value (if in the exact range 0..2^53 for Double and
> more for Extended). That may not be good enough.
>
>
> For integer powers, one can use a multiplying loop, though that would
> get slow for 1.000001^1000000 (which gives about e); in which case one
> can be cunning as in (written in Borland, but perhaps generic) -
>
> function ExpNum(const A : Xtype ; const B : longint) : Xtype ;
> begin if B=0 then ExpNum := 1.0 else
> if Odd(B) then ExpNum := ExpNum(A, B-1) * A
> else ExpNum := Sqr(ExpNum(A, B div 2)) ;
> end {ExpNum} ;
>
> which would for that do about log2(1000000) = 20 recursions. It could
> be rewritten iterative.
>
> My <URL:http://www.merlyn.demon.co.uk/pas-math.htm>
refers.
>
> With an integer number to be raised to a power, a multiplying loop can
> never take unreasonably long, unless the number is -1 0 +1 or runtime
> checks are off.
>
>
> But the actual answer to the OP is "NO" or "NOT IN TP".
Yes, Richard's solution requires real, but I need to use longint.
More precisely, I want to do a program that provides and stores the
reverse of a number. For example:
input: 12345
result: 54321
I am using div and mod to do that (with two longints and an array of
longint), and having not thought any other way I can do the above, I
can't use the elegant N^P= exp( P* ln(N) ); solution.
Is there any way I can do casting in Turbo Pascal 7.1 (like in C or C++)?
|
