标准库的randrandom随机数产生函数性能极差

1、有网文称c标准库的rand/random随机数产生函数性能极差。一直信以为真，但从没做过验证。最近因其他因缘，写了些代码专门验证rand/random的性能。结果大出意料，颠覆之前的成见。结论如下：1) rand/random性极佳。在64位机器上，其性能大约比简单自增略低30%(32位的自增比64位性能高出1倍以上)！2) srand/srandom性能极差极差。绝对不能每次调用rand之前都调用srand。这么做不仅没必要，还会极大降低性能，性能只有调用rand的1%！3) rand文档中提到的实现示例也实际实现存在差别，尤其是srand实现！4) rand的实现起始就是简单的乘法和取模，

2、简单的随机数实现在性能上几乎无法超越系统自带的标准实现！5) 网上的东西很多真是不靠谱！下面测试代码，代码在64/32位机器都能运行。编译命令：g+ -o3 -o test random.cpp 1 #include <stdio.h> 2 #include <stdint.h> 3 #include <vector> 4 #include <algorithm> 5 6 #include <stdlib.h> 7 #include <math.h> 8 9 #include <sys/time.h> 10 1

3、1 12 #define NUM_RAND_SEED 100 13 14 15 class Random 16 17 public: 18 static int srandom(size_t randSeedNum = NUM_RAND_SEED); 19 20 static size_t random(); 21 22 private: 23 static bool m_bInit; 24 static size_t m_count; 25 static std:vector<size_t> m_randSeeds; 26 ; 27 28 bool Random:m_bInit

4、= false; 29 size_t Random:m_count = 0; 30 std:vector<size_t> Random:m_randSeeds; 31 32 int Random:srandom( size_t randSeedNum ) 33 34 m_randSeeds.clear(); 35 36 for(size_t i=0; i< randSeedNum; +i) 37 m_randSeeds.push_back( i ); 38 39 40 std:random_shuffle(m_randSeeds.begin(), m_randSeeds.en

5、d(); 41 m_bInit = true; 42 43 printf("Random:srandomn"); 44 return 0; 45 46 47 size_t Random:random() 48 49 if( ! m_bInit ) 50 srandom(); 51 52 53 static size_t size = m_randSeeds.size(); 54 return 16777619 * m_randSeeds m_count + % size ; 55 56 /return 16777619 * m_randSeeds m_count + % N

6、UM_RAND_SEED ; 57 /return 16777619 * m_randSeeds (m_count +) & 0xffL ; 58 59 60 / 简单随机数 61 int MyRandom() 62 63 static struct timeval tv; 64 static size_t iCount = 0; 65 66 tv.tv_usec += 54321; 67 if( tv.tv_usec > 1000000) 68 tv.tv_usec -= 1000000; 69 70 if( iCount+ % 1000 = 0 ) 71 gettimeofd

7、ay(&tv, NULL); 72 73 74 return tv.tv_usec; 75 76 77 / 自增 78 int Inc() 79 80 static size_t iCount = 0; 81 82 return iCount+; 83 84 85 / 86 87 struct timeval stStartTv; 88 89 /return past time. uint: us 90 long PostTime(struct timeval *pstStartTv) 91 92 struct timeval stEndTv; 93 gettimeofday(&

8、;stEndTv, NULL); 94 struct timeval* pstCurrTv = &stEndTv; 95 96 long sec, usec = 0; 97 sec = pstCurrTv->tv_sec - pstStartTv->tv_sec; 98 if (usec = pstCurrTv->tv_usec - pstStartTv->tv_usec) < 0) 99 sec-;100 usec += 1000000;101 102 usec += sec*1000000;103 104 return usec;105 106 107

9、 void LogPastTime(struct timeval *pstStartTv, const char* sStep)108 109 long usec = PostTime(pstStartTv);110 111 printf("%s: Past time: %ld msn", sStep, usec / 1000);112 113 114 #define STAT_NUM 100115 116 / 自增函数117 void TestInc(size_t count)118 119 gettimeofday(&stStartTv, NULL);120 s

10、ize_t arrCountSTAT_NUM = 0;121 printf("Test Inc.n");122 123 for(size_t i=0; i<count; +i)124 size_t rand = Inc();125 arrCount rand % STAT_NUM +;126 127 128 printf("Total count: %lun", count);129 for(size_t i=0; i<STAT_NUM; +i)130 printf("%lu: count=%lu, ratio=%fn",

11、 i, arrCounti, arrCounti * 1.0 / count);131 132 133 LogPastTime(&stStartTv, "Inc");134 printf("Test Inc.n");135 136 137 / 简单自增138 void TestInc2(size_t count)139 140 gettimeofday(&stStartTv, NULL);141 size_t arrCountSTAT_NUM = 0;142 printf("Test Inc.n");143 144 s

12、tatic size_t icount = 0;145 for(size_t i=0; i<count; +i)146 size_t rand = icount +;147 arrCount rand % STAT_NUM +;148 149 150 printf("Total count: %lun", count);151 for(size_t i=0; i<STAT_NUM; +i)152 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count)

13、;153 154 155 LogPastTime(&stStartTv, "Inc");156 printf("Test Inc.n");157 158 159 / 160 void TestMyRandom(size_t count)161 162 Random:srandom(); / not cala time163 164 gettimeofday(&stStartTv, NULL);165 size_t arrCountSTAT_NUM = 0;166 printf("Test My Random.n");1

14、67 168 for(size_t i=0; i<count; +i)169 size_t rand = Random:random();170 arrCount rand % STAT_NUM +;171 172 173 printf("Total count: %lun", count);174 for(size_t i=0; i<STAT_NUM; +i)175 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count);176 177 178 L

15、ogPastTime(&stStartTv, "MyRandom");179 printf("Test My Random.n");180 181 182 / 简单随机数183 void TestSimpleRandom(size_t count)184 185 gettimeofday(&stStartTv, NULL);186 size_t arrCountSTAT_NUM = 0;187 printf("Test Simple Random.n");188 189 for(size_t i=0; i<cou

16、nt; +i)190 size_t rand = MyRandom();191 arrCount rand % STAT_NUM +;192 193 194 printf("Total count: %lun", count);195 for(size_t i=0; i<STAT_NUM; +i)196 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count);197 198 199 LogPastTime(&stStartTv, "Sim

17、ple Random");200 printf("Test Simple Random.n");201 202 203 / random204 void TestRandom(size_t count)205 206 gettimeofday(&stStartTv, NULL);207 size_t arrCountSTAT_NUM = 0;208 printf("Test Random.n");209 210 for(size_t i=0; i<count; +i)211 size_t rand = random();212 a

18、rrCount rand % STAT_NUM +;213 214 215 printf("Total count: %lun", count);216 for(size_t i=0; i<STAT_NUM; +i)217 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count);218 219 220 LogPastTime(&stStartTv, "Sys Random");221 printf("Test Rand

19、om.n");222 223 224 / rand225 void TestRand(size_t count)226 227 gettimeofday(&stStartTv, NULL);228 size_t arrCountSTAT_NUM = 0;229 printf("Test Rand.n");230 231 for(size_t i=0; i<count; +i)232 size_t r = rand();233 arrCount r % STAT_NUM +;234 235 236 printf("Total count: %

20、lun", count);237 for(size_t i=0; i<STAT_NUM; +i)238 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count);239 240 241 LogPastTime(&stStartTv, "Sys Rand");242 printf("Test Rand.n");243 244 245 / 调用srand 和rand246 void TestRand2(size_t coun

21、t)247 248 gettimeofday(&stStartTv, NULL);249 size_t arrCountSTAT_NUM = 0;250 printf("Test Rand (and srand).n");251 252 for(size_t i=0; i<count; +i)253 srand(i);254 size_t r = rand();255 arrCount r % STAT_NUM +;256 257 258 printf("Total count: %lun", count);259 for(size_t i=0; i<STAT_NUM; +i)260 printf("%lu: count=%lu, ratio=%fn", i, arrCounti, arrCounti * 1.0 / count);261 262 263 LogPastTime(&stStartTv, "Sys Rand");264 printf("Test Ran