Dividing numbers in PIC C - Page 2 - Electronic Circuits Projects Diagrams Free

Pommie · 27th September 2009, 06:56 AM

Your logic will work correctly up to 99 as this is the biggest BCD number than can be contained in a byte.

Mike.

Noggin · 27th September 2009, 01:06 PM

Quote:

Originally Posted by Pommie

I was saying that making all variables floats was a bloated way to achieve the desired outcome. In the example given, j needs to be a float, the others could be chars. Also, casting to double makes it extra obvious what is being done.

Mike.

In that case, then respectfully, I agree.

Pommie · 29th September 2009, 06:32 AM

Quote:

Originally Posted by Johnbear

I had to make all the variables in the calculation of type float for it to work.
-

You could have just done,

Code:

double j;
unsigned char i, Byte0, Byte1, Byte2, Byte3, x, y, z;
unsigned long FTW, bit32, Fo, Fref;

void main (void)
    { 
        y=5;
        z=2;
        j=(double)y/(double)z;
}

Mike.

Oznog · 2nd October 2009, 07:47 AM

Google for "Integer Promotion". This is an important term. Also search your compiler manual for this.

IP is a matter of C standards that all C compilers should either subscribe to, or list somewhere that they do something different. It comes down to several things:
1. It specifies where promotions to larger integers will occur. The left side of the equation never determines how the eq is interpreted during calculation. It's all the arguments on the right side. For equations which require multiple steps (add, mult, then divide), the type may even change multiple times.
2. Sometimes this automatic promotion will not be necessary, and consume excess resources to perform.
3. Some types of promotions, though potentially necessary for your application, are not done automatically. No one ever promotes an integer equation to a Float/Double.
4. Some types of promotion are unspecified by the standard and your compiler may or may not promote them.
5. You can often force the way integers are calculated by using a cast, but the compiler may overrule it in its actual implementation.

Also note that constants are evaluated and "folded" during the precompiler stage. As such, an integer may be assigned by a complicated calculation of float constants, either #defined as explicit constants or stated explicitly on the right hand side, and NO float code will be included in the program or executed. This is very handy at times for making clear code without making it any less efficient.

It is highly unlikely that you need a floating-point calc here. Everyone thinks they need FP early on, but rarely do. FP is quite slow to run, relatively speaking, and fixed-point type calculations can almost always do the job. In some cases they're more accurate, too.

You may find fixed-point math is easier and more efficient if you shift the value by considering it a mult/div of a power 2. You, as a programmer, will have to keep track of where the decimal is in the variable at any given time. Comment everywhere for documentation.

JAISHREE_KHATAR · 10th October 2009, 03:23 PM

Hello..
I am using pic 1937 in my project. I am using timer0 as an interrupt. Now the problem i am facing is : when timer0 overflows, the corresponding flag bit gets set.. then it must go into its service routine..but it is not entering into its service routine..just it overflows and flag gets set.. and it restarts. not going into its routine.. can anybody suggest any solution or hint regarding this?

thank you so much in advance..

Noggin · 10th October 2009, 10:56 PM

This doesn't have anything to do with division. Make a new topic and people will happily try to help you out.

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27th September 2009, 06:56 AM	#16
Pommie	Your logic will work correctly up to 99 as this is the biggest BCD number than can be contained in a byte. Mike.

2nd October 2009, 07:47 AM	#19
Oznog	Google for "Integer Promotion". This is an important term. Also search your compiler manual for this. IP is a matter of C standards that all C compilers should either subscribe to, or list somewhere that they do something different. It comes down to several things: 1. It specifies where promotions to larger integers will occur. The left side of the equation never determines how the eq is interpreted during calculation. It's all the arguments on the right side. For equations which require multiple steps (add, mult, then divide), the type may even change multiple times. 2. Sometimes this automatic promotion will not be necessary, and consume excess resources to perform. 3. Some types of promotions, though potentially necessary for your application, are not done automatically. No one ever promotes an integer equation to a Float/Double. 4. Some types of promotion are unspecified by the standard and your compiler may or may not promote them. 5. You can often force the way integers are calculated by using a cast, but the compiler may overrule it in its actual implementation. Also note that constants are evaluated and "folded" during the precompiler stage. As such, an integer may be assigned by a complicated calculation of float constants, either #defined as explicit constants or stated explicitly on the right hand side, and NO float code will be included in the program or executed. This is very handy at times for making clear code without making it any less efficient. It is highly unlikely that you need a floating-point calc here. Everyone thinks they need FP early on, but rarely do. FP is quite slow to run, relatively speaking, and fixed-point type calculations can almost always do the job. In some cases they're more accurate, too. You may find fixed-point math is easier and more efficient if you shift the value by considering it a mult/div of a power 2. You, as a programmer, will have to keep track of where the decimal is in the variable at any given time. Comment everywhere for documentation. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes. Last edited by Oznog; 2nd October 2009 at 07:59 AM.

10th October 2009, 03:23 PM	#20
JAISHREE_KHATAR	Pic 1937 timer problem Hello.. I am using pic 1937 in my project. I am using timer0 as an interrupt. Now the problem i am facing is : when timer0 overflows, the corresponding flag bit gets set.. then it must go into its service routine..but it is not entering into its service routine..just it overflows and flag gets set.. and it restarts. not going into its routine.. can anybody suggest any solution or hint regarding this? thank you so much in advance..

10th October 2009, 10:56 PM	#21
Noggin	This doesn't have anything to do with division. Make a new topic and people will happily try to help you out. __________________ A rectangular bear is just a polar bear after a coordinate transform. -- I dunno who. A recent study shows that research causes cancer in rats. -- I dunno who said that one either.