Complex Fixed-points in ANSI C

As I mentioned before, SystemC provides a series well-define classes for fixed-point. For more details I will summarize them and make a short intro in these days. Here, I'll show you another way, in ANSI C, to write for my own fixed-point simulation. And it's fully compatiable with gcc.
Here is my cmplx_fix.h (header file for complex fixed-point)


//+FHDR------------------------------------------------
// (C) Copyright Company NTHU.EE VLSI Comm Lab.2009
// All Right Reserved
//-----------------------------------------------------
// FILE NAME: cmplx_fix.h
// AUTHOR: stanlly9
// CONTACT INFORMATION: stanlly9.blogspot.com
//-----------------------------------------------------
// RELEASE VERSION: V 1.0
// VERSION DESCRIPTION:
// 1.0 First release
//-----------------------------------------------------
// RELEASE DATE: Mar-25-2009
//-----------------------------------------------------
// PURPOSE: Complex fixed point
//-FHDR------------------------------------------------

#ifndef _CMPLX_FX_HDR
#define _CMPLX_FX_HDR

#define IWL 7//integer word-length
#define DWL 9 //decimal fraction word-length
//IWL+DWL=sizeof(short int)*2=16
typedef struct {
short int re;
short int im;
} cmplx_fix;
//check negaitve
int is_neg(short int);
//cmplx_fix fcns
void cf_print(cmplx_fix);//printer
void cf_seti_re(cmplx_fix*, int);//set rel part by integer values
void cf_seti_im(cmplx_fix*, int);//set img part by integer values
void cf_setf_re(cmplx_fix*, float);//set rel part by float values
void cf_setf_im(cmplx_fix*, float);//set img part by float values

//--cmplx_fix operator fcns--
//----cmplx_fix to cmplx_fix----
cmplx_fix cf_add(cmplx_fix, cmplx_fix);// +
cmplx_fix cf_sub(cmplx_fix, cmplx_fix);// -
cmplx_fix cf_mul(cmplx_fix, cmplx_fix);// *
cmplx_fix cf_div(cmplx_fix, cmplx_fix);// /
//----cmplx_fix to integer values----
cmplx_fix cf_add_re(cmplx_fix, int); // + real
cmplx_fix cf_add_im(cmplx_fix, int); // + imag
//cmplx_fix cf_sub_re(cmplx_fix, int); // - real as _add_re(-int)
//cmplx_fix cf_sub_im(cmplx_fix, int); // - imag as _add_im(-int)
cmplx_fix cf_mul_re(cmplx_fix, int); // * real
cmplx_fix cf_mul_im(cmplx_fix, int); // * imag
cmplx_fix cf_div_re(cmplx_fix, int); // / real
cmplx_fix cf_div_im(cmplx_fix, int); // / imag
#endif


In ANSI C, we don't have much useful programming shortcuts,
no classes, no functional overridding, no operator overridding, etc
All things we can do is function calls, such as the function:
cf_print() is self-made print function.
cf_add() is the func for my cmplx_fix addition.

For the cmplx_fix structure contains two members:
re is the real part
im is the imalge part
They are in a short int datatypes(signed 16bits each) for reducing memory allocation.
The interger word-length is define by IWL, decimal fraction part by DWL

In these version, I do not perform the overflow and stratuation processing.
It may be improved in the future.
The cmplx_fix addition function cf_add() is shwon as an example here:
//cmplx_fix + cmplx_fix
cmplx_fix cf_add(cmplx_fix a, cmplx_fix b)
{
short int real = a.re + b.re;
short int imag = a.im + b.im;
a.re = (short int) real;
a.im = (short int) imag;
return a;
}