diff options
Diffstat (limited to 'handy.h')
| -rw-r--r-- | handy.h | 72 |
1 files changed, 63 insertions, 9 deletions
@@ -2967,21 +2967,75 @@ last-inclusive range. * are very useful when you want an integer to "dance" in a random way, * but you also never want it to become 0 and thus false. * - * Obviously they leave x unchanged if it starts out as 0. */ + * Obviously they leave x unchanged if it starts out as 0. + * + * We have two variants just because that can be helpful in certain + * places. There is no advantage to either, they are equally bad as each + * other as far RNG's go. Sufficiently random for many purposes, but + * insufficiently random for serious use as they fail important tests in + * the Test01 BigCrush RNG test suite by L’Ecuyer and Simard. (Note + * that Drand48 also fails BigCrush). The main point is they produce + * different sequences and in places where we want some randomlike + * behavior they are cheap and easy. + * + * Marsaglia was one of the early researchers into RNG testing and wrote + * the Diehard RNG test suite, which after his death become the + * Dieharder RNG suite, and was generally supplanted by the Test01 suite + * by L'Ecruyer and associates. + * + * There are dozens of shift parameters that create a pseudo random ring + * of integers 1..2^N-1, if you need a different sequence just read the + * paper and select a set of parameters. In fact, simply reversing the + * shift order from L/R/L to R/L/R should result in another valid + * example, but read the paper before you do that. + * + * PDF of the original paper: + * https://www.jstatsoft.org/article/download/v008i14/916 + * Wikipedia: + * https://en.wikipedia.org/wiki/Xorshift + * Criticism: + * https://www.iro.umontreal.ca/~lecuyer/myftp/papers/xorshift.pdf + * Test01: + * http://simul.iro.umontreal.ca/testu01/tu01.html + * Diehard: + * https://en.wikipedia.org/wiki/Diehard_tests + * Dieharder: + * https://webhome.phy.duke.edu/~rgb/General/rand_rate/rand_rate.abs + * + */ -#define PERL_XORSHIFT64(x) \ +/* 32 bit version */ +#define PERL_XORSHIFT32_A(x) \ STMT_START { \ - (x) ^= (x) << 13; \ - (x) ^= (x) >> 17; \ - (x) ^= (x) << 5; \ + (x) ^= ((x) << 13); \ + (x) ^= ((x) >> 17); \ + (x) ^= ((x) << 5); \ +} STMT_END + +/* 64 bit version */ +#define PERL_XORSHIFT64_A(x) \ +STMT_START { \ + (x) ^= ((x) << 13); \ + (x) ^= ((x) >> 7); \ + (x) ^= ((x) << 17); \ } STMT_END /* 32 bit version */ -#define PERL_XORSHIFT32(x) \ +#define PERL_XORSHIFT32_B(x) \ +STMT_START { \ + (x) ^= ((x) << 5); \ + (x) ^= ((x) >> 27); \ + (x) ^= ((x) << 8); \ +} STMT_END + +/* 64 bit version - currently this is unused, + * it is provided here to complement the 32 bit _B + * variant which IS used. */ +#define PERL_XORSHIFT64_B(x) \ STMT_START { \ - (x) ^= (x) << 13; \ - (x) ^= (x) >> 7; \ - (x) ^= (x) << 17; \ + (x) ^= ((x) << 15); \ + (x) ^= ((x) >> 49); \ + (x) ^= ((x) << 26); \ } STMT_END |