SQRT Problem.

This is a discussion on SQRT Problem. within the C Programming forums, part of the General Programming Boards category; Code: long DesvioPadrao(long pesos[100], u16_t tamanho) { double ld_raiz; long total = 0; long media; long ll_resultado; int iCont; char ...

  1. #1
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    SQRT Problem.

    Code:
    long DesvioPadrao(long pesos[100], u16_t tamanho)
    {
    	double ld_raiz;
    	long total = 0;
    	long media;
    	long ll_resultado;
    	int iCont;
    
    	char strTexto[100];
    
    	for(iCont=0; iCont<tamanho; iCont++)
    		total += pesos[iCont];
    
    	media = total / tamanho;
    	total = 0;
    
    	for(iCont=0; iCont<tamanho; iCont++)
    	{
    		ll_resultado = pesos[iCont] - media;
    		total = total + (ll_resultado * ll_resultado);
    	}
    
    	total = (long) total / (tamanho - 1);
    
           /*
           here total = 10
           */
    	ld_raiz = sqrt(total);
    
    	total = (long)ld_raiz;
    	return total;
    }
    My function return 528062108, when i call SQRT function passing value 10 like argument, and cast (or no cast) to long.

  2. #2
    Bit Fiddler
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    sqrt takes a double as argument, not long.
    Code:
    ld_raiz = sqrt((double) total);

  3. #3
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    Quote Originally Posted by Fader_Berg View Post
    sqrt takes a double as argument, not long.
    Code:
    ld_raiz = sqrt((double) total);
    The problems continue..

  4. #4
    C++ Witch laserlight's Avatar
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    Post the smallest and simplest compilable program that demonstrates the problem. Also, post your input, expected output and actual output.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    Quote Originally Posted by Fader_Berg View Post
    sqrt takes a double as argument, not long.
    Code:
    ld_raiz = sqrt((double) total);
    Type promotion should happily convert the long value to a double before making the call, so nothing to worry about there.

  6. #6
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    Maybe, my enviroment get an error...
    a simple sqrt(2); showed in "%d" on a printf get same error.

  7. #7
    C++ Witch laserlight's Avatar
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    What is the error? Are you sure you are compiling as C?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  8. #8
    Bit Fiddler
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    Quote Originally Posted by sergioms View Post
    Maybe, my enviroment get an error...
    a simple sqrt(2); showed in "%d" on a printf get same error.
    You can't print doubles with %d [printf("%d", sqrt(2))], you must use %lf.

  9. #9
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    Yes, i'm compiling by GCC ARM using Yargato lib.
    YAGARTO - Yet another GNU ARM toolchain

  10. #10
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    QUOTE=Fader_Berg; You can't print doubles with %d [printf("%d", sqrt(2))], you must use %lf.

  11. #11
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    Quote Originally Posted by Adak View Post
    QUOTE=Fader_Berg; You can't print doubles with %d [printf("%d", sqrt(2))], you must use %lf.
    erros continue...

  12. #12
    Bit Fiddler
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    Code:
    printf("%lf", sqrt(2))
    ...doesn't give you the right answer?

  13. #13
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    Code:
    unsigned long isqrt(const unsigned long n);
    
    /*-- isqrt -----------------------------------------------------------------*/
    
    unsigned long isqrt(unsigned long n) {
      unsigned long s, t;
    
    #define sqrtBit(k) \
      t = s+(1UL<<(k-1)); t <<= k+1; if (n >= t) { n -= t; s |= 1UL<<k; }
    
      s = 0UL;
    #ifdef __alpha
      if (n >= 1UL<<62) { n -= 1UL<<62; s = 1UL<<31; }
      sqrtBit(30); sqrtBit(29); sqrtBit(28); sqrtBit(27); sqrtBit(26);
      sqrtBit(25); sqrtBit(24); sqrtBit(23); sqrtBit(22); sqrtBit(21);
      sqrtBit(20); sqrtBit(19); sqrtBit(18); sqrtBit(17); sqrtBit(16);
      sqrtBit(15);
    #else
      if (n >= 1UL<<30) { n -= 1UL<<30; s = 1UL<<15; }
    #endif
      sqrtBit(14); sqrtBit(13); sqrtBit(12); sqrtBit(11); sqrtBit(10);
      sqrtBit(9); sqrtBit(8); sqrtBit(7); sqrtBit(6); sqrtBit(5);
      sqrtBit(4); sqrtBit(3); sqrtBit(2); sqrtBit(1);
      if (n > s<<1) s |= 1UL;
    
    #undef sqrtBit
    
      return s;
    }

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