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28 #include "RandomNumber.h"
30 #include "CryptographicallyRandomNumber.h"
31 #include "RandomNumberSeed.h"
38 #if USE(MERSENNE_TWISTER_19937)
40 #include "mt19937ar.c"
48 #if USE(OS_RANDOMNESS)
49 uint32_t bits = cryptographicallyRandomNumber();
50 return static_cast<double>(bits) / (static_cast<double>(std::numeric_limits<uint32_t>::max()) + 1.0);
52 // Without OS_RANDOMNESS, we fall back to other random number generators
53 // that might not be cryptographically secure. Ideally, most ports would
54 // define USE(OS_RANDOMNESS).
56 #if USE(MERSENNE_TWISTER_19937)
57 return genrand_res53();
59 uint32_t part1 = rand() & (RAND_MAX - 1);
60 uint32_t part2 = rand() & (RAND_MAX - 1);
61 // rand only provides 31 bits, and the low order bits of that aren't very random
62 // so we take the high 26 bits of part 1, and the high 27 bits of part2.
63 part1 >>= 5; // drop the low 5 bits
64 part2 >>= 4; // drop the low 4 bits
65 uint64_t fullRandom = part1;
69 // Mask off the low 53bits
70 fullRandom &= (1LL << 53) - 1;
71 return static_cast<double>(fullRandom)/static_cast<double>(1LL << 53);