系统编程实验lab2--位操作 bit manipulate
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直接上代码：
1 /* 2 * bits.c - Source file with your solutions to the Lab. 3 * This is the file you will hand in to your instructor. 4 */ 5 6 #include "btest.h" 7 #include <limits.h> 8 9 /* 10 * Instructions to Students: 11 * 12 * STEP 1: Fill in the following struct with your identifying info. 13 */ 14 info_struct info = 15 { 16 /* Replace with your full name */ 17 "huangmenglin", 18 /* Replace with your login ID */ 19 "2016141463199", 20 }; 21 22 #if 0 23 /* 24 * STEP 2: Read the following instructions carefully. 25 */ 26 27 You will provide your solution to the Data Lab by 28 editing the collection of functions in this source file. 29 30 CODING RULES: 31 32 Replace the "return" statement in each function with one 33 or more lines of C code that implements the function. Your code 34 must conform to the following style: 35 36 int Funct(arg1, arg2, ...) { 37 /* brief description of how your implementation works */ 38 int var1 = Expr1; 39 ... 40 int varM = ExprM; 41 42 varJ = ExprJ; 43 ... 44 varN = ExprN; 45 return ExprR; 46 } 47 48 Each "Expr" is an expression using ONLY the following: 49 1. Integer constants 0 through 255 (0xFF), inclusive. 50 ***You are not allowed to use big constants such as 0xffffffff*** 51 2. Function arguments and local variables (no global variables). 52 3. Unary integer operations ! ~ 53 4. Binary integer operations & ^ | + << >> 54 55 Some of the problems restrict the set of allowed operators even further. 56 Each "Expr" may consist of multiple operators. You are not restricted to 57 one operator per line. 58 59 You are expressly forbidden to: 60 1. Use any control constructs such as if, do, while, for, switch, etc. 61 2. Define or use any macros. 62 3. Define any additional functions in this file. 63 4. Call any functions. 64 5. Use any other operations, such as &&, ||, -, ?, or []: 65 6. Use any form of casting. 66 67 You may assume that your machine: 68 1. Uses 2s complement, 32-bit representations of integers. 69 2. Performs right shifts arithmetically. 70 3. Has unpredictable behavior when shifting an integer by more 71 than the word size. 72 73 EXAMPLES OF ACCEPTABLE CODING STYLE: 74 /* 75 * pow2plus1 - returns 2^x + 1, where 0 <= x <= 31 76 */ 77 int pow2plus1(int x) { 78 /* exploit ability of shifts to compute powers of 2 */ 79 return (1 << x) + 1; 80 } 81 82 /* 83 * pow2plus4 - returns 2^x + 4, where 0 <= x <= 31 84 */ 85 int pow2plus4(int x) { 86 /* exploit ability of shifts to compute powers of 2 */ 87 int result = (1 << x); 88 result += 4; 89 return result; 90 } 91 92 93 NOTES AND HINTS: 94 1. Each function has a maximum number of operators (! ~ & ^ | + << >>) 95 that you are allowed to use for your implementation of the function. 96 The max operator count will be checked by your instructor. 97 Note that ‘=‘ is not counted; you may use as many of these as you 98 want without penalty. 99 2. Use the btest test harness to check your functions for correctness. 100 #endif 101 102 /* 103 * STEP 3: Modify the following functions according the coding rules. 104 */ 105 106 107 108 /* 109 * bitAnd - x&y using only ~ and | 110 * Example: bitAnd(6, 5) = 4 111 * Legal ops: ~ | 112 * Max ops: 8 113 * Rating: 1 114 */ 115 int bitAnd(int x, int y) { 116 117 int x1 = ~x; 118 int y1 = ~y; 119 int res = ~(x1|y1); 120 return res; 121 122 } 123 124 125 126 127 128 129 /* 130 * bitOr - x|y using only ~ and & 131 * Example: bitOr(6, 5) = 7 132 * Legal ops: ~ & 133 * Max ops: 8 134 * Rating: 1 135 */ 136 int bitOr(int x, int y) { 137 int x1 = ~x; 138 int y1 = ~y; 139 int res = ~(x1&y1); 140 return res; 141 } 142 143 144 145 146 147 148 /* 149 * isZero - returns 1 if x == 0, and 0 otherwise 150 * Examples: isZero(5) = 0, isZero(0) = 1 151 * Legal ops: ! ~ & ^ | + << >> 152 * Max ops: 2 153 * Rating: 1 154 */ 155 int isZero(int x) { 156 return !x; //？x不能过65535 157 158 } 159 160 161 162 163 164 165 /* 166 * minusOne - return a value of -1 167 * Legal ops: ! ~ & ^ | + << >> 168 * Max ops: 2 169 * Rating: 1 170 */ 171 int minusOne(void) { 172 char c=255; 173 return c; 174 } 175 176 177 178 179 180 181 /* 182 * TMax - return maximum two‘s complement integer 183 * Legal ops: ! ~ & ^ | + << >> 184 * Max ops: 4 185 * Rating: 1 186 */ 187 int tmax(void) { 188 int a = 1; 189 int b = minusOne(); 190 191 return b^(a<<31); 192 } 193 194 195 196 197 198 199 200 /* 201 * bitXor - x^y using only ~ and & 202 * Example: bitXor(4, 5) = 1 203 * Legal ops: ~ & 204 * Max ops: 14 205 * Rating: 2 206 */ 207 int bitXor(int x, int y) { 208 209 int a = ~x; 210 int b = ~y; 211 return (a&y)|(x&b); 212 213 } 214 215 216 217 218 219 220 /* 221 * getByte - Extract byte n from word x 222 * Bytes numbered from 0 (LSB) to 3 (MSB) 223 * Examples: getByte(0x12345678,1) = 0x56 224 * Legal ops: ! ~ & ^ | + << >> 225 * Max ops: 6 226 * Rating: 2 227 */ 228 int getByte(int x, int n) { 229 int a = 255; 230 x = x>>(n*8); 231 return a&x; 232 } 233 234 235 236 237 238 239 /* 240 * isEqual - return 1 if x == y, and 0 otherwise 241 * Examples: isEqual(5,5) = 1, isEqual(4,5) = 0 242 * Legal ops: ! ~ & ^ | + << >> 243 * Max ops: 5 244 * Rating: 2 245 */ 246 int isEqual(int x, int y) { 247 248 return !(x^y); 249 250 } 251 252 253 254 255 256 257 /* 258 * negate - return -x 259 * Example: negate(1) = -1. 260 * Legal ops: ! ~ & ^ | + << >> 261 * Max ops: 5 262 * Rating: 2 263 */ 264 int negate(int x) { 265 int res = (~x)+1; 266 return res; 267 } 268 269 270 271 272 /* 273 * isPositive - return 1 if x > 0, return 0 otherwise 274 * Example: isPositive(-1) = 0. 275 * Legal ops: ! ~ & ^ | + << >> 276 * Max ops: 8 277 * Rating: 3 278 */ 279 int isPositive(int x) { 280 //return x&(!(x>>31)); 为什么不行，超过65535 = 2^16-1就不行了？ 281 return !((!x)|(x>>31)); //就算超过，也可以，!X只管0 282 }
其中值得注意的是，c语言规定非零数表示true（1）其实是有范围的，最大不能超过65535，最小不能小于-65535。
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