Syntax for pow function using inline C

[espruino-discuss3]

Posted at 2018-08-26 by Robin

Sun 2018.08.26

I am attempting to write some simple inline C functions. Was able to get the first snippet 'How do I use it' to compile and run.

http://www.espruino.com/InlineC

I'm now attempting the 'C' pow() function but wonder where to place the #include statement
#include <math.h>
Wouldn't you know it, this post machine wont allow the lt math.h gl symbology

#include <math.h>

Not under: either [http://www.espruino.com/Compilation](http://www.espruino.com/Compilation)

It can't be placed outside the var c = E.compiledC( block as it's not recognized as Javascript, and placing it inside results in this compiler msg:

COMPILER MESSAGE
---------------------------------------------------
out4261837251.cpp:60:1: error: stray '#' in program
 #include <math.h>
 ^
out4261837251.cpp:60:2: error: 'include' does not name a type
 #include <math.h>

                                 COMPILER MESSAGE
---------------------------------------------------
out1319183279.cpp: In function 'int calc(int)':
out1319183279.cpp:71:26: error: 'pow' was not declared in this scope
  float dP = pow(dR,dG);

var cg = E.compiledC(`
// int calc(int)

#include  <math.h>

int calc(int n){
 float dR = float(n) / 255.0;
 float dP = pow(dR,dG);

var cg = E.compiledC(`
// int calc(int)
#include <math.h>
int calc(int n){
float dR = float(n) / 255.0;
float dP = pow(dR,dG);

Need the insight of someone that's been down this path.
A pow er user ;-)

Thankx

[espruino-discuss3]

Posted at 2018-08-26 by @allObjects

...since there is no C preprocessor to resolve #define - see Caveats in 'Inline C code', there is also no #include. The issue is that the service the way it is implemented right now would not know from where to include from... May be this could change when callbakc-url could be passed and you can serve your things to include by a (public) Web server... (you are exposing your dev source thru http).

---

Posted at 2018-08-26 by Robin

Sun 2018.08.26

Yeah, read that but on:

http://www.espruino.com/Compilation

What works and what doesn't?
Works
Maths, string operations

What part of using a math function isn't 'Maths' ?

and wasn't sure if an extension was similar to a module

http://www.espruino.com/Extending+Espruino+1

#include referenced there, so went on a hunch

Wonder if I could accomplish the same task with a function that iterates using brute force += multiplication? Hmmmm

---

Posted at 2018-08-28 by @gfwilliams

http://www.espruino.com/Compilation is about compiling JS code, not inline C which is http://www.espruino.com/InlineC

http://www.espruino.com/Extending+Esprui­no+1 is about compiling your own version if Espruino - in which case you can include what you want.

The preprocessor is disabled because:

• it's a potential security hole (#include "/etc/passwd")
• including things will almost certainly bring in a lot of extra code and/or memory requirements that will probably use enough RAM that it makes it unusable anyway.

I guess you're just compiling a pow function for fun? Because there's one already in Math.pow.

If I were doing it, I'd:

• Google c implementation of pow
• Copy the code from https://stackoverflow.com/questions/101439/the-most-efficient-way-to-implement-an-integer-based-power-function-powint-int
• Paste it into the example from http://www.espruino.com/InlineC

var c = E.compiledC(`
// int ipow(int,int)
int ipow(int base, int exp)
{
    int result = 1;
    for (;;)
    {
        if (exp & 1)
            result *= base;
        exp >>= 1;
        if (!exp)
            break;
        base *= base;
    }

    return result;
}
`);

print(c.ipow(5,5));

As mentioned in InlineC though, you may have similar issues dealing with double arithmetic though, since the double maths functions won't get built in by default.