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Diffstat (limited to '')
-rw-r--r-- | mysys/my_rnd.c | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/mysys/my_rnd.c b/mysys/my_rnd.c new file mode 100644 index 00000000..b1dd8b1f --- /dev/null +++ b/mysys/my_rnd.c @@ -0,0 +1,66 @@ +/* Copyright (C) 2007 MySQL AB & Michael Widenius + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */ + +#include "mysys_priv.h" +#include <my_rnd.h> +#include <m_string.h> + +/* + Initialize random generator + + NOTES + MySQL's password checks depends on this, so don't do any changes + that changes the random numbers that are generated! +*/ + +void my_rnd_init(struct my_rnd_struct *rand_st, ulong seed1, ulong seed2) +{ +#ifdef HAVE_valgrind + bzero((char*) rand_st,sizeof(*rand_st)); /* Avoid UMC varnings */ +#endif + rand_st->max_value= 0x3FFFFFFFL; + rand_st->max_value_dbl=(double) rand_st->max_value; + rand_st->seed1=seed1%rand_st->max_value ; + rand_st->seed2=seed2%rand_st->max_value; +} + + +/* + Generate random number. + + SYNOPSIS + my_rnd() + rand_st INOUT Structure used for number generation + + RETURN VALUE + generated pseudo random number + + NOTE: + This is codes so that it can be called by two threads at the same time + with minimum impact. + (As the number is supposed to be random, it doesn't matter much if + rand->seed1 or rand->seed2 are updated with slightly wrong numbers or + if two threads gets the same number. +*/ + +double my_rnd(struct my_rnd_struct *rand_st) +{ + unsigned long seed1; + seed1= (rand_st->seed1*3+rand_st->seed2) % rand_st->max_value; + rand_st->seed2=(seed1+rand_st->seed2+33) % rand_st->max_value; + rand_st->seed1= seed1; + return (((double) seed1)/rand_st->max_value_dbl); +} + |