83 lines
1.8 KiB
C
83 lines
1.8 KiB
C
#include "init_random_seed.h"
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#include <stdlib.h>
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#include <stdint.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <sys/time.h>
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#include <unistd.h>
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/* basic PRNG to use for improving the basic seed selection */
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static unsigned lcg (uint64_t seed)
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{
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if (0 ==seed)
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{
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seed = UINT64_C(104729);
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}
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else
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{
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seed %= UINT64_C(4294967296);
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}
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seed = (seed * UINT64_C(279470273)) % UINT64_C(4294967291);
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return seed % UINT64_MAX;
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}
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/* Generate a good PRNG seed value */
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void init_random_seed(void)
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{
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unsigned seed = 0u;
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int have_seed = 0;
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// try /dev/urandom for an initial seed
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int random_source;
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if ((random_source = open ("/dev/urandom", O_RDONLY)) >= 0)
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{
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size_t random_data_length = 0;
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have_seed = -1;
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while (random_data_length < sizeof seed)
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{
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ssize_t result = read (random_source, &seed + random_data_length, (sizeof seed) - random_data_length);
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if (result < 0)
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{
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// error, unable to read /dev/random
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have_seed = 0;
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}
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random_data_length += result;
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}
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close (random_source);
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}
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if (!have_seed)
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{
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// fallback to combining the time and PID in a fairly random way
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pid_t pid = getpid ();
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struct timeval tv;
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gettimeofday (&tv, NULL);
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seed = (unsigned)(((unsigned)pid << 16)
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^ (unsigned)pid
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^ (unsigned)tv.tv_sec
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^ (unsigned)tv.tv_usec);
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seed = lcg (seed);
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}
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srand (seed);
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}
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#ifdef TEST
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#include <stdio.h>
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int main (int argc, char * argv[])
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{
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init_random_seed ();
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int i, j;
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int r[10][4];
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for (i = 0; i < 10; ++i)
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{
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for (j = 0; j < 4; ++j)
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{
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printf ("%10d ", rand ());
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}
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printf ("\n");
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}
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return 0;
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}
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#endif
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