OpenEuphoria

Re: Pass C double to Eu shared library

• Posted by jimcbrown (admin) May 12, 2012
• 1510 views

Euphoria shared dynamically loading library can also be used by C programs as long as only 31-bit integer values are exchanged.  
If a 32-bit pointer or integer must be passed, and you have the source to the C program, you could pass the value in  
two separate 16-bit integer arguments (upper 16 bits and lower 16 bits), and then combine the values in the Euphoria  
routine into the desired 32-bit atom.  

-- Eu Code 
export function MyFunc(sequence x) 
  ? x 
end function 

// C Code 
extern MyFunc(double x[]) 
 
int main() { 
double x[4] = {1.1,2.2,3.3,4.4}; 
MyFunc(x); 
return 0; 
} 

On the Euphoria side,

-- Eu Code 
export function MyFunc(integer a, integer b, integer len) 
  -- preamble to handle conversion 
  atom p = (a * 65536) + b 
  sequence x = {} 
  for i = 0 to (len-1)*8 by 8 do 
	sequence d = peek({p+i, 8}) 
	x &= float64_to_atom(d) 
  done 
  -- end preamble 
  ? x 
end function 

(Sadly, 4.0 seems to lack a peek_float64_array(). Otherwise we could do this:

-- Eu Code 
export function MyFunc(integer a, integer b, integer len) 
  -- preamble to handle conversion 
  atom p = (a * 65536) + b 
  sequence x = peek_float64_array(p, len) 
  -- end preamble 
  ? x 
end function 

)

On the C side,

// C Code 
extern void MyFunc(int a, int b, int len) 
 
int main() { 
double x[4] = {1.1,2.2,3.3,4.4}; 
intptr_t d, a, b; 
d = (intptr_t)x; 
b = d & 0xFFFF; 
a = d & 0xFFFF0000; 
a = a >> 16; 
MyFunc(a, b, 4); 
return 0; 
} 

Or even,

// C Code 
extern void MyFunc(int a, int b, int len) 
void MyFuncWrapper(double x[], int len) 
{ 
intptr_t d, a, b; 
d = (intptr_t)x; 
b = d & 0xFFFF; 
a = d & 0xFFFF0000; 
a = a >> 16; 
MyFunc(a, b, 4); 
} 
 
int main() { 
double x[4] = {1.1,2.2,3.3,4.4}; 
MyFuncWrapper(x, 4); 
return 0; 
}