ICS datalab总结

/* 
 * bitAnd - x&y using only ~ and | 
 *   Example: bitAnd(6, 5) = 4
 *   Legal ops: ~ |
 *   Max ops: 8
 *   Rating: 1
 */
int bitAnd(int x, int y) {
	return ~(~x|~y);
}
/* 
 * getByte - Extract byte n from word x
 *   Bytes numbered from 0 (LSB) to 3 (MSB)
 *   Examples: getByte(0x12345678,1) = 0x56
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 6
 *   Rating: 2
 */
int getByte(int x, int n) {
	int t=0xff;
	return t&(x>>(n<<3));
}
/* 
 * logicalShift - shift x to the right by n, using a logical shift
 *   Can assume that 0 <= n <= 31
 *   Examples: logicalShift(0x87654321,4) = 0x08765432
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 20
 *   Rating: 3 
 */
int logicalShift(int x, int n) {
	int t=(1<<31)&x;
	return (x>>n)^((t>>n)<<1);
}	
/*
 * 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 sum=0;
	int Mask=1|(1<<8);
    Mask=Mask|(Mask<<16);
	sum=x&Mask;
	sum+=(x>>1)&Mask;
	sum+=(x>>2)&Mask;
	sum+=(x>>3)&Mask;
	sum+=(x>>4)&Mask;
	sum+=(x>>5)&Mask;
	sum+=(x>>6)&Mask;
	sum+=(x>>7)&Mask;
	sum+=(sum>>16);
	sum+=(sum>>8);
	return sum&0xff;
}
/* 
 * bang - Compute !x without using !
 *   Examples: bang(3) = 0, bang(0) = 1
 *   Legal ops: ~ & ^ | + << >>
 *   Max ops: 12
 *   Rating: 4 
 */
int bang(int x) {
	
	return ((~(x|(~x+1)))>>31)&1;
}
/* 
 * tmin - return minimum two's complement integer 
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 4
 *   Rating: 1
 */
int tmin(void) {
	return (1<<31);
}
/* 
 * 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 t=33+(~n);
    return !(x^((x<>t));
}
/* 
 * divpwr2 - Compute x/(2^n), for 0 <= n <= 30
 *  Round toward zero
 *   Examples: divpwr2(15,1) = 7, divpwr2(-33,4) = -2
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 15
 *   Rating: 2
 */
int divpwr2(int x, int n) {
	int bias=(x>>31)&((1<>n;
}
/* 
 * negate - return -x 
 *   Example: negate(1) = -1.
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 5
 *   Rating: 2
 */
int negate(int x) {
  return (~x+1);
}
/* 
 * isPositive - return 1 if x > 0, return 0 otherwise 
 *   Example: isPositive(-1) = 0.
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 8
 *   Rating: 3
 */
int isPositive(int x) {
	
  return !((x>>31)|(!x));
}
/* 
 * isLessOrEqual - if x <= y  then return 1, else return 0 
 *   Example: isLessOrEqual(4,5) = 1.
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 24
 *   Rating: 3
 */
int isLessOrEqual(int x, int y) {
	int signx=x>>31;  
	int signy=y>>31;  
	int signSame=((x+(~y))>>31)&(!(signx^signy));  
	int signDiffer=signx&(!signy);  
	return signDiffer|signSame;  
}
/*
 * ilog2 - return floor(log base 2 of x), where x > 0
 *   Example: ilog2(16) = 4
 *   Legal ops: ! ~ & ^ | + << >>
 *   Max ops: 90
 *   Rating: 4
 */
int ilog2(int x) {
	int sum1,sum2,sum3,sum4,sum5;
	sum1=(!!(x>>16))<<4;
	x=x>>sum1;
	sum2=(!!(x>>8))<<3;
	x=x>>sum2;
	sum3=(!!(x>>4))<<2;
	x=x>>sum3;
	sum4=(!!(x>>2))<<1;
	x=x>>sum4;
	sum5=(!!(x>>1));
	return sum1+sum2+sum3+sum4+sum5;
}
/* 
 * float_neg - Return bit-level equivalent of expression -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 representations of
 *   single-precision floating point values.
 *   When argument is NaN, return argument.
 *   Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
 *   Max ops: 10
 *   Rating: 2
 */
unsigned float_neg(unsigned uf) {
	unsigned result=uf^0x80000000;
	if((uf&0x7fffffff)>0x7f800000)
		result=uf;
	return result;
}
/* 
 * float_i2f - Return bit-level equivalent of expression (float) x
 *   Result is returned as unsigned int, but
 *   it is to be interpreted as the bit-level representation of a
 *   single-precision floating point values.
 *   Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
 *   Max ops: 30
 *   Rating: 4
 */
unsigned float_i2f(int x) {
		unsigned sign=0,shiftleft=1,flag=0;  
		unsigned absx=x;  
		if( x==0 ) return 0;  
		if( x<0 )
		{  
			sign=0x80000000;  
			absx=(~x+1);  
		}  
		while((absx&0x80000000)==0)
		{
			absx<<=1;  
			shiftleft++;  
		}  
		absx<<=1;
		if( (absx & 0x01ff) > 0x0100 ) flag=1;	
		if( (absx & 0x03ff) == 0x0300 ) flag=1;	
		return sign+(absx>>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 e = uf & 0x7F800000;    
    unsigned sign = uf & 0x80000000;    
    if (e) {    
       if (  e != 0x7F800000 ) {  
          uf = uf + 0x00800000;      
        }  
    }  
    else  
       uf = ( uf << 1) | sign ; 
    return uf;  
}