tar xvf datalab-handout.tar解压缩之后可以看到本次实验使用的是gcc工具,打开Makefile文件可以看到使用了-m32进行了编译
所以如果在编译的时候报错了还需要安装32位的gcc编译器
sudo apt-get install gcc-multilib位运算运算符优先级
| 运算符 | 优先级 |
|---|---|
| () | 1 |
| -(单目) ! ~ | 2 |
| * / % | 3 |
| + - | 4 |
| << >> | 5 |
| > >= < <= | 6 |
| == != | 7 |
| & | 8 |
| ^ | 9 |
| | | 10 |
int bitXor(int x, int y) {
return ~(x&y)&~(~x&~y);
}
/*
* tmin - return minimum two's complement integer
Legal ops: ! ~ & ^ | + << >>
Max ops: 4
Rating: 1
*/
int tmin(void) {
return 1<<31;
}
//2
/*
* isTmax - returns 1 if x is the maximum, two's complement number,
and 0 otherwise
Legal ops: ! ~ & ^ | +
Max ops: 10
Rating: 1
*/
int isTmax(int x) {
return !((~(x+1)^x))&!!(x+1);
}
/*
* allOddBits - return 1 if all odd-numbered bits in word set to 1
where bits are numbered from 0 (least significant) to 31 (most significant)
Examples allOddBits(0xFFFFFFFD) = 0, allOddBits(0xAAAAAAAA) = 1
Legal ops: ! ~ & ^ | + << >>
Max ops: 12
Rating: 2
*/
int allOddBits(int x) {
int mask = 0xaa | 0xaa << 8;
mask = mask | mask << 16;
return !((x&mask)^mask);
}
/*
* negate - return -x
Example: negate(1) = -1.
Legal ops: ! ~ & ^ | + << >>
Max ops: 5
Rating: 2
*/
int negate(int x) {
return ~x+1;
}
//3
/*
* isAsciiDigit - return 1 if 0x30 <= x <= 0x39 (ASCII codes for characters '0' to '9')
Example: isAsciiDigit(0x35) = 1.
isAsciiDigit(0x3a) = 0.
isAsciiDigit(0x05) = 0.
Legal ops: ! ~ & ^ | + << >>
Max ops: 15
Rating: 3
*/
int isAsciiDigit(int x) {
int first_match = !(x>>4^3);
int second_match = (~0xa+1+(x&0xf))>>31&1;
return first_match & second_match;
}
/*
* conditional - same as x ? y : z
Example: conditional(2,4,5) = 4
Legal ops: ! ~ & ^ | + << >>
Max ops: 16
Rating: 3
*/
int conditional(int x, int y, int z) {
int mask = !x + ~0;
return (mask & y) | (~mask &z);
}
/*
* 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 judge = !((y+~x+1)>>31);
int same_signal = !((x^y)>>31);
int x_neg_y_pos = (x>>31)&!(y>>31);
return x_neg_y_pos | (same_signal & judge);
}
//4
/*
* logicalNeg - implement the ! operator, using all of
the legal operators except !
Examples: logicalNeg(3) = 0, logicalNeg(0) = 1
Legal ops: ~ & ^ | + << >>
Max ops: 12
Rating: 4
*/
int logicalNeg(int x) {
int a = (x&(~x+1));
int b = a + ~0;
int c = b >> 31;
return ~c + 1;
}
/* howManyBits - return the minimum number of bits required to represent x in
two's complement
Examples: howManyBits(12) = 5
howManyBits(298) = 10
howManyBits(-5) = 4
howManyBits(0) = 1
howManyBits(-1) = 1
howManyBits(0x80000000) = 32
Legal ops: ! ~ & ^ | + << >>
Max ops: 90
Rating: 4
*/
int howManyBits(int x) {
int b16,b8,b4,b2,b1,b0;
int flag = x>>31;
x = (flag&~x) | (~flag&x); //x为非正数则不变 ,x 为负数 则相当于按位取反
b16 = !!(x>>16) <<4; //如果高16位不为0,则我们让b16=16
x>>=b16; //如果高16位不为0 则我们右移动16位 来看高16位的情况
//下面过程基本类似
b8=!!(x>>8)<<3;
x >>= b8;
b4 = !!(x >> 4) << 2;
x >>= b4;
b2 = !!(x >> 2) << 1;
x >>= b2;
b1 = !!(x >> 1);
x >>= b1;
b0 = x;
return b0+b1+b2+b4+b8+b16+1;
}
//float
/*
* floatScale2 - 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 floatScale2(unsigned uf) {
int exp_mask = 0x7f800000;
int exp = (uf&exp_mask)>>23;
int frac_mask = 0x7fffff;
int frac = uf & frac_mask;
if (exp == 0) {
if (frac>>23&1) {
frac = frac * 2 - 0x7fffff;
} else {
frac = frac << 1;
}
return (uf & ~frac_mask) | frac;
} else if (exp == 255) {
return uf;
} else {
return (uf & ~exp_mask) | (exp+1)<<23;
}
}
/*
* floatFloat2Int - Return bit-level equivalent of expression (int) f
for floating point argument f.
Argument is passed as unsigned int, but
it is to be interpreted as the bit-level representation of a
single-precision floating point value.
Anything out of range (including NaN and infinity) should return
0x80000000u.
Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while
Max ops: 30
Rating: 4
*/
int floatFloat2Int(unsigned uf) {
int exp_mask = 0x7f800000;
int frac_mask = 0x7fffff;
int exp = (uf & exp_mask)>>23;
int frac = uf & frac_mask;
int signal = uf>>31&1;
int bias;
int ans;
if (exp < 127) {
return 0;
} else if (exp == 255 || exp > 127+31) {
return 0x80000000;
} else {
if (exp==127+31){
if (frac==0 && signal == 1) {
return 0x80000000;
} else {
return 0x80000000;
}
} else {
bias = exp-127;
if (bias >= 23) {
ans = (1<<bias) + (1<<bias>>23)*frac;
} else {
ans = 1<<bias;
}
return signal ? -ans:ans;
}
}
}
/*
* floatPower2 - Return bit-level equivalent of the expression 2.0^x
(2.0 raised to the power x) for any 32-bit integer x.
*
The unsigned value that is returned should have the identical bit
representation as the single-precision floating-point number 2.0^x.
If the result is too small to be represented as a denorm, return
0. If too large, return +INF.
*
Legal ops: Any integer/unsigned operations incl. ||, &&. Also if, while
Max ops: 30
Rating: 4
*/
unsigned floatPower2(int x) {
int frac, exp;
if (x < -149) return 0;
else if (x >= -149 && x <= -127) {
frac = x+149;
return 1 << frac;
} else if (x<128) {
exp = x+127;
return exp << 23;
} else {
return 255 << 23;
}
}我自己的做的时候 howManyBits 不知道怎么做,上网查的答案
其他的题目也都不是特别困难,看一下位运算应该也可以看懂
make
# 编译会有一个警告,忽略即可
# 检查正确性,如果没有输出则说明所有函数实现符合要求,否则需要修改
./dlc bits.c
./btestroot@da1811a84ddc:~/csapplabs/01Data Lab/datalab-handout# ./dlc bits.c
root@da1811a84ddc:~/csapplabs/01Data Lab/datalab-handout# ./btest
Score Rating Errors Function
1 1 0 bitXor
1 1 0 tmin
1 1 0 isTmax
2 2 0 allOddBits
2 2 0 negate
3 3 0 isAsciiDigit
3 3 0 conditional
3 3 0 isLessOrEqual
4 4 0 logicalNeg
4 4 0 howManyBits
4 4 0 floatScale2
4 4 0 floatFloat2Int
ERROR: Test floatPower2 failed.
Timed out after 10 secs (probably infinite loop)
Total points: 32/36最后的 floatPower2 超时是因为测试案例太多了,修改btest.c中的TIMEOUT_LIMIT宏,重新编译后通过
// btest.c
#define TIMEOUT_LIMIT 20root@da1811a84ddc:~/csapplabs/01Data Lab/datalab-handout# ./btest
Score Rating Errors Function
1 1 0 bitXor
1 1 0 tmin
1 1 0 isTmax
2 2 0 allOddBits
2 2 0 negate
3 3 0 isAsciiDigit
3 3 0 conditional
3 3 0 isLessOrEqual
4 4 0 logicalNeg
4 4 0 howManyBits
4 4 0 floatScale2
4 4 0 floatFloat2Int
4 4 0 floatPower2
Total points: 36/36关于浮点数的知识笔者留下的印象也不多了,故特做了一文计算机系统基础：浮点数的表示