ex9_5.c

自己做的常用库和实现的数据结构。public domain.

/*
  Ex9_5
  Set a certain field of an int by a function called-- BIT_SET --
*/
int int_size(test)
unsigned int test;
{
   int bitlenth=0;

   while ( test!=0 )
   {
       test /= 2;
       bitlenth += 1;
   }
   return(bitlenth);
}

bit_set(pic,value,n,length)
int *pic;                /* point at an int */
int value;               /* value to be set in a certain field */
int n;                   /* the field start at bit_n */
int length;              /* length of the field */
{
    int set;             /* temp var to set the field all in '1' */

    set = ~(~0<< length);
    *pic = (( set & value )<< n) | ( ~(set << n)& (*pic));
                         /* above formular*/
                         /* front part-- set the value in the field
                                         other fields are in'0'     */
                         /* back part -- reset '0' in the field
                                         others of the int reserved */
}

main()
{
    int one;             /* An int to be used in bit_set */
    unsigned int  test=~0;
    int v,start,l;

    printf("---Ans905 ---\n");
    printf("Input one int : set_value : start_field : length\n");
    scanf("%d %d %d %d",&one,&v,&start,&l);

    if ( start+l > int_size(test) )
       printf( " The length of your bits is longer than the int_size of this\
machine!\n");
    else
       bit_set(&one,v,start,l);

    printf("=== RESULT ===   : %d\td %o\to %x\tx\n",one,one,one);
}