CODEWITHSUNDEEP
cnumbersfixed-point
phhe
phhe

Reputation: 209

Fixed point numbers in C without float

In C is it possible to present a fixed point number in binary form so it can be transmitted without the use floats ?

I know how to convert a float or double to the desired fixed point representation but I'm stuck when it shall be done without floating points. The problem is that the system I have to develop on has this limitation.

My idea is to create a struct which holds the full representation and a processable integer and fractional part. And after creating the struct with either only the received binary representation or the integer and fractional values there shall be a function which does the conversion.

Update:

My Question seems not to be precise enough so I'll add some details.

Within my code I have to create and receive Numbers in a certain fixed point representation. As described by the answers below this is nothing but a pointer to a sequence of bits. My problem is that i have to create this sequence of bits when sending or interpret it when receiving the information.

This conversion is my problem ignoring signdness it is quiet easy thing to do when you can use a float to convert from (code not tested, but must work like this):

float sourceValue = 12.223445;    
int intPart = 0;
float fractPart = 0.0;
//integer part is easy, just cast it
intPart = (int)sourceValue;
//the fractinoal part is the rest
fractPart = sourceValue - intPart;


//multipling the fract part by the precision of the fixed point number (Q9.25)
//gets us the fractional part in the desired representation
u_int64_t factor = 1;
factor = factor << 25;
u_int64_t fractPart = fractPart * factor;

The rest can be done by some shifting and the use of logical bit operators.

But how can I do this without a float in the middle, starting with something like this:

int intPart = 12;
int fractPart = 223445;

Is it even possible ? As told, I'm kind a stuck here.

Thanks for your help!

Upvotes: 0

Views: 1932

Answers (2)

glglgl
glglgl

Reputation: 91027

I don't know what you are really up to, but a fixed-point number can be viewed as an integer number with a constant factor applied to it.

For example, if you want to express a number in the interval [0; 1) in 16 bits, you can map it to the range [0; 65536) by simply multiplying it with 65536.

This said, it completely depends on how your integer values look like and how they are intended to be represented. In almost any case, you can apply a multiplication or division to it and are done.

Upvotes: 1

n3rd4n1
n3rd4n1

Reputation: 371

Everything boils down to bits, be it an integer, float, etc. All you need is the memory base address and the size of that certain memory. For example,

float src = 0.5;
float dest;
char bytes[sizeof(src)];    

memcpy(bytes, &num, sizeof(src));
dest = *((float *)bytes);

should give you dest equal to src.

Hope this helped.

Upvotes: 0

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