• State Not Answered
  • Locked Locked
  • Replies 11 replies
  • Subscribers 22 subscribers
  • Views 1389 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Arithametics

Deepak P

Hi All,

I am experiencing a basic problem in the arithametic of the instrucation

A = ((B-C)*100)/204

during execution of the instruction, if the result of (B-C)*100 is greater than 16 bits what will happen? for avoiding data loss do I have to declare it as 32 bit variable or the proceesor will handle it without changing the size?

Variable A is declared as 16 bit.

do I have to use both B and C 32 bit if i conditionally change the instrucation as

A = ((C-B)*100)/204

during execution ?

my code will look like this


if (B>C) A = ((B-C)*100)/204;

else if (C>B) A = ((C-B)*100)/204 ;

my processor is C8051F020
compiler is C51

best regards
Deepak

Parents
  • 0 in reply to Deepak P

    "if i am going to calculate the intermediate result separately it will need one more variable and code size will also increase"

    With a decent, modern, optimising compiler like C51, that is most unlikely!

    If you need to accomodate long values, then that's the code you need - there's no getting around it.

    Have you followed Hans-Bernhard Broeker's advice yet and gone back to your 'C' textbook to see how these things work?
    Again, It's standard 'C' - nothing specifically to do with Keil.

    With some suitable casting, you can force the compiler to use long arithmetic to do the calculation without having to introduce intermediate variables...

Reply
  • 0 in reply to Deepak P

    "if i am going to calculate the intermediate result separately it will need one more variable and code size will also increase"

    With a decent, modern, optimising compiler like C51, that is most unlikely!

    If you need to accomodate long values, then that's the code you need - there's no getting around it.

    Have you followed Hans-Bernhard Broeker's advice yet and gone back to your 'C' textbook to see how these things work?
    Again, It's standard 'C' - nothing specifically to do with Keil.

    With some suitable casting, you can force the compiler to use long arithmetic to do the calculation without having to introduce intermediate variables...

Children
  • 0 in reply to Andy Neil

    Hi,

    Please bear with me .. I know this is not where I have to discuss about standard 'C'. But sorry for that because here no body is near me to help me out with C coding and am very new to 'C' just like a kid learning to Walk !! I used to do it in assembly only.

    I tried Hans-Bernhard Broeker's advice and it worked. Thanks Mr. Hans-Bernhard Broeker.
    Thank you all for taking ur valuable time for me.
    If you don't mind give one more help. I have defined 100 in that code with a name HUNDRED to avoide usage of 'magic number' in the code. but .. how should i use Mr. Hans-Bernhard Broeker's advice with the define???

    Really sorry for bothering you all

    thanks
    Deepak

  • 0 in reply to Deepak P

    I have defined 100 in that code with a name HUNDRED to avoide usage of 'magic number'.
    That makes no sense. Naming 100 'HUNDRED' serves no purpose. If you were to change it, you would have to change the name as well. I have not studied your app, but names like CORRECTION_FACTOR, CONVERSION_CONSTANT comes to mind.

    If it under ALL circumstances has to be 100, then leave it as that, if it may change, give it 'functional name' not 'value name'

    Erik

  • 0 in reply to Deepak P

    does "A = (long)((C-B)*100L)/204"
    do the expected thing?