diff options
Diffstat (limited to 'builtin.c')
| -rw-r--r-- | builtin.c | 21 |
1 files changed, 20 insertions, 1 deletions
@@ -2372,6 +2372,8 @@ static char *const state = (char *const) istate; NODE * do_rand(int nargs ATTRIBUTE_UNUSED) { + double tmprand; +#define RAND_DIVISOR ((double)GAWK_RANDOM_MAX+1.0) if (firstrand) { (void) initstate((unsigned) 1, state, SIZEOF_STATE); /* don't need to srandom(1), initstate() does it for us. */ @@ -2383,7 +2385,24 @@ do_rand(int nargs ATTRIBUTE_UNUSED) * * 0 <= n < 1 */ - return make_number((AWKNUM) (random() % GAWK_RANDOM_MAX) / GAWK_RANDOM_MAX); + /* + * Date: Wed, 28 Aug 2013 17:52:46 -0700 + * From: Bob Jewett <jewett@bill.scs.agilent.com> + * + * Call random() twice to fill in more bits in the value + * of the double. Also, there is a bug in random() such + * that when the values of successive values are combined + * like (rand1*rand2)^2, (rand3*rand4)^2, ... the + * resulting time series is not white noise. The + * following also seems to fix that bug. + * + * The add/subtract 0.5 keeps small bits from filling + * below 2^-53 in the double, not that anyone should be + * looking down there. + */ + + tmprand = 0.5 + ( (random()/RAND_DIVISOR + random()) / RAND_DIVISOR); + return make_number((AWKNUM) (tmprand - 0.5)); } /* do_srand --- seed the random number generator */ |