Binary output

un2008 · #1 26-Mar-2008, 13:44

I am trying to write a program that displays all the bits of the binary representation of the type float.

The program needs to display info like this Example. (User enters the number 6).

This program displays a binary representation of real numbers.
Enter a real number: 6

The number's representation is 32 bits long:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
01000000110000000000000000000000
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

sign: 0
exponent: 10000001
mantissa: 10000000000000000000000

Notes:
To display the bits I have to use the for loop.

There is a skeleton program which has to be used and only edited within int main:

CPP / C++ / C Code:

/****************************************************************
* skeleton program file float.cpp 
* This program calculate calculates and displays a binary
*   representation of real numbers.
* Assume all input is of the correct format.
*
* Input:  a real number.
*
* Output: The bit pattern of the number stored in the computer's
*    memory as float
*
* Processing: 
*         .......
*
* Author: 
*
********************************************************************/

#include <iostream>         // for cin and cout
#include <iomanip>          // for setw()
using namespace std;

// prototype
int TestBit( unsigned bit, float number );

// start of the program
int main() 
{


    return 0;

} // of main()


/*
* TestBit: tests bits of a float number
* receive: a bit where 0 is the rightmost bit
*         and a number to test
* return: 1 if the bit is set on, 0 therwise
* preconditions: bit is in the range 0..31
*/
int TestBit( unsigned bit, float number )
{
	if ( bit < 8*sizeof(number) )
		if ( ((( unsigned int) 1) << bit) & (*((unsigned int*)(&number))) )
			return 1;
	return 0;
	
} // TestBit

I am completely lost. I do not understand how to write a for loop into it or return the particular bit of the float number. I have spent days trying to work it out. If anyone could help by giving me an example of how it works or showing me how to do it I would really appreciate it.
I have done all of the formatting and the prompt for real number etc (i think), I am just stuck on the 0's and 1's parts. It has just completely gone over my head.

Thank you.

fakepoo · #2 26-Mar-2008, 15:44

Assuming that your TestBit() function is working, here is how you would write a loop:

CPP / C++ / C Code:

unsigned i;
float f = 2.25;

for(i=0;i<32;++i) cout << TestBit(i,f);

Peter_APIIT · #3 26-Mar-2008, 18:55

I wonder how to output binary number instead of integer.

Thanks.

fakepoo · #4 27-Mar-2008, 07:34

Quote:

Originally Posted by Peter_APIIT

I wonder how to output binary number instead of integer.

Thanks.

I wrote this function some time ago. It converts a byte to a binary string. For example, it would convert 0xF3 to "1111 0011".

CPP / C++ / C Code:

string ByteToString( unsigned char byte )
{	int i;
	string result = "";
	unsigned char mask = 0x80;

	for(i=0;i<8;i++)
	{	result = result + ((byte&mask)? "1" : "0");
		mask >>= 1;
		if(i == 3) result = result + " ";
	}
	return result;
}

I'm sure that it could easily be changed to handle integers instead of bytes.

davekw7x · #5 27-Mar-2008, 09:15

Quote:

Originally Posted by un2008

... I do not understand how to write a for loop into it or return the particular bit of the float number

I have to assume that you didn't write TestBits(). Maybe it was given to you??

Anyhow, assume for the moment that it works as "advertised" in the comments.

Then...

Since the function returns the value of a bit at position given by the value of the second argument, and, assuming that the bit positions of a floating point number are 31 (for the highest bit position) down to zero (for the lowest bit position), couldn't you look at the bits with something like the following:

CPP / C++ / C Code:

    float x = 6.0;
    cout << "The value of x is " << x << endl;
    cout << "Here are the bits:\n  ";
    for (int i = 31; i >= 0; i--) 
    {
        cout << TestBit(i, x);
    }
    cout << endl;

Try that to get a feel for it:

Code:

The value of x is 6
Here are the bits:
  01000000110000000000000000000000

Now, if you want to capture the bits in an array so that you can break out the components of the floating point number (sign, exponent, etc.), couldn't you simply make the loop:

CPP / C++ / C Code:

    int bits[32];
    for (int i = 31; i >= 0; i--) 
    {
        bits[i] = TestBit(i, x);
    }

Then bits[31] is the sign; bits[30] through bits[23] are the exponent, etc. Right?

Regards,

Dave

Footnote: Why did I put "mantissa" between quote marks? Because it is not really the "mantissa" as usually defined for scientific notation. The official designation is, I think, "significand." But "mantissa" is commonly used although it is not technically correct. See the following for more details: http://en.wikipedia.org/wiki/Floating_point

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