modf ( )【C语言库函数源代码】

【C语言库函数源代码】

【本程序在Dev C++ 4.9.9.2 下编译通过】

/*

   将浮点数x分解成整数部分和小数部分。

   返回小数部分，将整数部分存入* iptr所指内存中。

*/

double my_modf01(double x, double *iptr)

{

   double ret = fmod(x,1.0);

   *iptr = x - ret;

   return ret;

}//这个函数算法比较简单，也容易让人理解。

 

//下面的这个函数理解起来就有点困难了。

 

typedef struct

{

   unsigned int mantissal:32;

   unsigned int mantissah:20;

   unsigned int exponent:11;

   unsigned int sign:1;

}double_t;//这个结构体在IEEE.h定义。

double my_modf02(double x, double *y)

{

   double_t * z = (double_t *)&x;

   double_t * iptr = (double_t *)y;

 

   int j0;

   unsigned int i;

   j0 = z->exponent - 0x3ff;  /* exponent of x */ 

   if(j0<20)

   {/* integer part in high x */

      if(j0<0)

      {                  /* |x|<1 */

        *y = 0.0;

        iptr->sign = z->sign;

        return x;

      }

      else

      {

        if ( z->mantissah == 0 && z->mantissal == 0 )

        {

           *y = x;

           return 0.0;

        }

        i = (0x000fffff)>>j0;

        iptr->sign = z->sign;

        iptr->exponent = z->exponent;

        iptr->mantissah = z->mantissah&(~i);

        iptr->mantissal = 0;

        if ( x == *y )

        {

           x = 0.0;

           z->sign = iptr->sign;

           return x;

        }         

              return x - *y;       

      }

   }

   else if (j0>51)

   {             /* no fraction part */

      *y = x;

      if ( isnan(x) || isinf(x) )

        return x;

      x = 0.0;

      z->sign = iptr->sign;

      return x;

   }

   else

   {                        /* fraction part in low x */

      i = ((unsigned)(0xffffffff))>>(j0-20);

      iptr->sign = z->sign;

      iptr->exponent = z->exponent;

      iptr->mantissah = z->mantissah;

      iptr->mantissal = z->mantissal&(~i);

      if ( x == *y )

      {

        x = 0.0;

        z->sign = iptr->sign;

        return x;

      }

      return x - *y;       

   }

}

//下面是两个要用到的函数

int isnan(double d)

{

   union

   {

      unsigned long long l;

      double d;

   } u;

   u.d=d;

   return (u.l==0x7FF8000000000000ll || u.l==0x7FF0000000000000ll || u.l==0xfff8000000000000ll);

}

int isinf(double d)

{

   union

   {

      unsigned long long l;

      double d;

   } u;

   u.d=d;

   return (u.l==0x7FF0000000000000ll?1:u.l==0xFFF0000000000000ll?-1:0);

}

 

int main()

{

   double x,y;

  

   x = 12345678901.1234567;

 

   printf("%f = (%f) + (%f) \n",x,y,modf(x,&y));

   printf("%f = (%f) + (%f) \n",x,y,my_modf01(x,&y));

   printf("%f = (%f) + (%f) \n",x,y,my_modf02(x,&y));

  

   printf("\n******************************************\n");

  

   printf("%f = (%f) + (%f) \n",-x,y,modf(-x,&y));

   printf("%f = (%f) + (%f) \n",-x,y,my_modf01(-x,&y));

   printf("%f = (%f) + (%f) \n",-x,y,my_modf02(-x,&y));

  

   system("pause");

   return 0;

}