digitalmars.D.learn - Custom Exponents

Malkierian (7/7) Dec 14 2013 Alright, so I'm trying to do hex string to integer conversion,

Malkierian (4/12) Dec 14 2013 Well, I made my own pow function to use for now, but it seems
=?UTF-8?B?QWxpIMOHZWhyZWxp?= (4/10) Dec 14 2013 There is an operator for that: :)
Nathan M. Swan (4/10) Dec 14 2013 http://dlang.org/phobos/std_math.html#.pow

Malkierian (4/20) Dec 14 2013 Gah, why didn't I search pow in that page... I HAD looked there
Philippe Sigaud (1/3) Dec 14 2013 Is there any difference between using `a ^^ b` and `pow(a,b)`?
Andrej Mitrovic (47/52) Dec 15 2013 Depends on whether the arguments are known at compile-time, and their
Philippe Sigaud (3/14) Dec 15 2013 Ugh. I agree.

Marco Leise (5/16) Dec 15 2013 dmd lacks a native implementation of ^^ and replaces it with pow() or so...

Marco Leise (14/21) Dec 15 2013 Hi. I'm an efficiency guy. May I suggest using an algorithm

"Malkierian" <rhydonj gmail.com> writes:

Alright, so I'm trying to do hex string to integer conversion, 
but I can't for the live of me find how to do exponent 
calculation in D.  Java has a Math.pow() function that allows you 
to specify the base and the exponent, but all I've seen in D's 
libraries are functions that allow you to only specify the 
exponent and does it on a predetermined base, such as 2, e or 10. 
  I need 16 for the base.

Dec 14 2013

"Malkierian" <rhydonj gmail.com> writes:

On Sunday, 15 December 2013 at 05:22:47 UTC, Malkierian wrote:
 Alright, so I'm trying to do hex string to integer conversion, 
 but I can't for the live of me find how to do exponent 
 calculation in D.  Java has a Math.pow() function that allows 
 you to specify the base and the exponent, but all I've seen in 
 D's libraries are functions that allow you to only specify the 
 exponent and does it on a predetermined base, such as 2, e or 
 10.
  I need 16 for the base.

Well, I made my own pow function to use for now, but it seems 
kind of stupid to me that that's not in the standard library.  I 
must be missing something.

Dec 14 2013

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 12/14/2013 09:22 PM, Malkierian wrote:
 Alright, so I'm trying to do hex string to integer conversion, but I
 can't for the live of me find how to do exponent calculation in D.  Java
 has a Math.pow() function that allows you to specify the base and the
 exponent, but all I've seen in D's libraries are functions that allow
 you to only specify the exponent and does it on a predetermined base,
 such as 2, e or 10.  I need 16 for the base.

There is an operator for that: :)

     assert(16 ^^ 2 == 256);

Ali

Dec 14 2013

"Nathan M. Swan" <nathanmswan gmail.com> writes:

On 12/14/13 8:22 PM, Malkierian wrote:
 Alright, so I'm trying to do hex string to integer conversion, but I
 can't for the live of me find how to do exponent calculation in D.  Java
 has a Math.pow() function that allows you to specify the base and the
 exponent, but all I've seen in D's libraries are functions that allow
 you to only specify the exponent and does it on a predetermined base,
 such as 2, e or 10.  I need 16 for the base.



See the fourth overload: `if (isFloatingPoint!F && isFloatingPoint!G)`.

NMS

Dec 14 2013

"Malkierian" <rhydonj gmail.com> writes:

On Sunday, 15 December 2013 at 05:39:03 UTC, Nathan M. Swan wrote:
 On 12/14/13 8:22 PM, Malkierian wrote:
 Alright, so I'm trying to do hex string to integer conversion, 
 but I
 can't for the live of me find how to do exponent calculation 
 in D.  Java
 has a Math.pow() function that allows you to specify the base 
 and the
 exponent, but all I've seen in D's libraries are functions 
 that allow
 you to only specify the exponent and does it on a 
 predetermined base,
 such as 2, e or 10.  I need 16 for the base.



 See the fourth overload: `if (isFloatingPoint!F && 
 isFloatingPoint!G)`.

 NMS

Gah, why didn't I search pow in that page...  I HAD looked there 
before...

Exponent should be somewhere in the description of that function.

Dec 14 2013

Philippe Sigaud <philippe.sigaud gmail.com> writes:



 See the fourth overload: `if (isFloatingPoint!F && isFloatingPoint!G)`.

Is there any difference between using `a ^^ b` and `pow(a,b)`?

Dec 14 2013

Andrej Mitrovic <andrej.mitrovich gmail.com> writes:

On 12/15/13, Philippe Sigaud <philippe.sigaud gmail.com> wrote:


 See the fourth overload: `if (isFloatingPoint!F && isFloatingPoint!G)`.

 Is there any difference between using `a ^^ b` and `pow(a,b)`?

Depends on whether the arguments are known at compile-time, and their
type. And in fact.. constant folding also affects what works
regardless of what you type something with, so initializers are taken
into account. Some demonstrations:

-----
void main()
{
    int a = 2, b = 2;
    auto c = a ^^ b;
}
-----

test.d(6): Error: must import std.math to use ^^ operator

The following will work though, probably through some compiler intrinsic:

-----
void main()
{
    enum a = 2, b = 2;
    auto c = a ^^ b;
}
-----

Here's where things get interesting. The following works:

-----
void main()
{
    enum float a = 1.0;
    enum float b = 2.1;
    auto c = a ^^ b;
}
-----

But the following doesn't:

-----
void main()
{
    enum float a = 1.1;  // note the .1 change
    enum float b = 2.1;
    auto c = a ^^ b;
}
-----

So even if you type something as `enum float a = 1.0`, the compiler
will be able to implicitly convert it to an int and it will make the
call work.

It seems like the intrinsic supports int^^int, int^^float, and
float^^int, but not float^^float.

Side-note: Importing std.stdio implicitly imports std.math, so you
won't have any errors (boy do I hate public imports where they don't
belong..).

Dec 15 2013

Philippe Sigaud <philippe.sigaud gmail.com> writes:

 -----
 void main()
 {
     int a = 2, b = 2;
     auto c = a ^^ b;
 }
 -----

 test.d(6): Error: must import std.math to use ^^ operator

?? The ^^ operator is defined in std.math?


 Side-note: Importing std.stdio implicitly imports std.math, so you
 won't have any errors (boy do I hate public imports where they don't
 belong..).

Ugh. I agree.
How does std.stdio imports std.math?

Dec 15 2013

Marco Leise <Marco.Leise gmx.de> writes:

Am Sun, 15 Dec 2013 13:52:55 +0100
schrieb Philippe Sigaud <philippe.sigaud gmail.com>:

 -----
 void main()
 {
     int a = 2, b = 2;
     auto c = a ^^ b;
 }
 -----

 test.d(6): Error: must import std.math to use ^^ operator

 
 ?? The ^^ operator is defined in std.math?

dmd lacks a native implementation of ^^ and replaces it with pow() or something.

-- 
Marco

Dec 15 2013

Marco Leise <Marco.Leise gmx.de> writes:

Am Sun, 15 Dec 2013 06:22:45 +0100
schrieb "Malkierian" <rhydonj gmail.com>:

 Alright, so I'm trying to do hex string to integer conversion, 
 but I can't for the live of me find how to do exponent 
 calculation in D.  Java has a Math.pow() function that allows you 
 to specify the base and the exponent, but all I've seen in D's 
 libraries are functions that allow you to only specify the 
 exponent and does it on a predetermined base, such as 2, e or 10. 
   I need 16 for the base.

Hi. I'm an efficiency guy. May I suggest using an algorithm
that closer matches what the machine can do? Instead of:

  result += hexValue(s[i]) * 16 ^^ (s.length-1 - i);

you could write

  result *= 16;
  result += hexValue(s[i]);

since general exponent calculations are not supported by the
integer arithmetic unit of the CPU, ^^ or pow will do a lot of
extra multiplications when you could get away with only one
each step.

-- 
Marco

Dec 15 2013

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