C语言datalab实验求解

Question

在做C语言的Datalab实验时有几个函数的功能看不明白，在网上找到了大神的代码，但是还是看不太懂，请教各位大神以下4个函数的作用以及代码
/*

• bitCount - returns count of number of 1's in word
• Examples: bitCount(5) = 2, bitCount(7) = 3
• Legal ops: ! ~ & ^ | + << >>
• Max ops: 40
• Rating: 4 */ int bitCount(int x) { //???? int result;
  //int mask1=(0x55)|(0x55<>1)&mask1);
  //add every four bits
  result=(result&mask2)+((result>>2)&mask2);
  //add every eight bits
  //result=(result&mask3)+((result>>4)&mask3);
  result=(result+(result>>4))&mask3;
  //add every sixteen bits
  //result=(result&mask4)+((result>>8)&mask4);
  result=(result+(result>>8))&mask4;
  //add every thirty two bits
  //result=(result&mask5)+((result>>16)&mask5);
  result=(result+(result>>16))&mask5;
  return result;
  }

/*

• fitsBits - return 1 if x can be represented as an
• n-bit, two's complement integer.
• 1 <= n <= 32
• Examples: fitsBits(5,3) = 0, fitsBits(-4,3) = 1
• Legal ops: ! ~ & ^ | + << >>
• Max ops: 15
• Rating: 2 */ int fitsBits(int x, int n) { //????? int shiftNumber = ~n + 33;
  return !(x^((x << shiftNumber) >> shiftNumber)); }

unsigned float_i2f(int x) { //??????
unsigned shiftLeft = 0;

unsigned afterShift, tmp, flag;

unsigned absX = x;

unsigned sign = 0;

//special case

if (x == 0) return 0;

//if x < 0, sign = 1000...,abs_x = -x

if (x < 0) {

sign=0x80000000;

absX = -x;

}

afterShift=absX;

//count shift_left and after_shift

while (1) {

tmp = afterShift;

afterShift<<=1;

shiftLeft++;

if (tmp & 0x80000000) break;

}

if ((afterShift & 0x01ff) > 0x0100)

flag = 1;

else if ((afterShift & 0x03ff) == 0x0300)

flag = 1;

else

flag = 0;

    return sign + (afterShift >> 9) + ((159 - shiftLeft) << 23) + flag;  

}

/*

• float_twice - Return bit-level equivalent of expression 2*f for
• floating point argument f.
• Both the argument and result are passed as unsigned int's, but
• they are to be interpreted as the bit-level representation of
• single-precision floating point values.
• When argument is NaN, return argument
• Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
• Max ops: 30
• Rating: 4 /
  unsigned float_twice(unsigned uf) { //????? unsigned f=uf;
  / Computer 2*f. If f is a NaN, then return f. /
  if ((f & 0x7F800000) == 0){
  //shift one bit to left
  f = ((f & 0x007FFFFF) << 1) | (0x80000000 & f);
  }
  else if ((f & 0x7F800000) != 0x7F800000){
  / Float has a special exponent. /
  / Increment exponent, effectively multiplying by 2. */
  f = f + 0x00800000;
  }
  return f;
  }

Answer 1

bitCount - returns count of number of 1's in word
在一个word（双字节）里找二进制为1的个数
fitsBits - return 1 if x can be represented as an
n-bit, two's complement integer.判断x是否可以表示为一个n位，2的补码的整数
float_twice - Return bit-level equivalent of expression 2*f for
floating point argument f.
对于浮点参数f返回2*f的位级别的等价形式