OK, this is a bit of guessing, and I would like to think that I've guessed wrongly because someone else *should* have hit this before...
On Sun, Feb 05, 2017 at 03:21:12PM -0800, Michael Schaap wrote: > # New Ticket Created by Michael Schaap > # Please include the string: [perl #130723] > # in the subject line of all future correspondence about this issue. > # <URL: https://rt.perl.org/Ticket/Display.html?id=130723 > > > > On my self-compiled Linux build of Rakudo Star 2017.01: > > % perl6 -e 'say (-524288..^524288).pick(50)' > (445052 -427 442649 66610 133030 238409 -250288 438259 508787 423778 > 90030 28568 -372417 143522 -335109 -156474 -395940 -124515 517779 398864 > -494020 -303173 -4646 253705 -263919 204704 328943 -230539 276553 > -142475 -311381 -224414 410534 -58726 -27584 -135264 -222462 79964 > -177401 -413056 -279021 -445158 -161601 61337 -101262 -66850 -285553 > -506522 366891 289163) > > This looks pretty normal. > > But on my Windows machine, using the 64-bit version of Rakudo Star > 2017.01, downloaded from http://rakudo.org/downloads/star/ , I get: > > % perl6 -e 'say (-524288..^524288).pick(50)' > (-504365 -504962 -520900 -503012 -504515 -514927 -524063 -511982 -503130 > -511610 -515842 -518903 -505137 -513172 -504845 -512334 -513608 -518507 > -512159 -508672 -492893 -503150 -501718 -515295 -495598 -513483 -507283 > -493687 -494653 -498803 -497266 -519193 -510278 -503827 -501717 -514772 > -507593 -500763 -509913 -509046 -523590 -516283 -499038 -501134 -499195 > -496352 -495618 -522092 -504550 -498746) > > I.e., I consistently get numbers close to the bottom end of the range. Windows. Random numbers. 3rdparty/libtommath/bn_mp_rand.c has: /* first place a random non-zero digit */ do { d = ((mp_digit) abs (MP_GEN_RANDOM())) & MP_MASK; } while (d == 0); if ((res = mp_add_d (a, d, a)) != MP_OKAY) { return res; } while (--digits > 0) { if ((res = mp_lshd (a, 1)) != MP_OKAY) { return res; } if ((res = mp_add_d (a, ((mp_digit) abs (MP_GEN_RANDOM())), a)) != MP_OKAY) { return res; } } 3rdparty/libtommath/tommath.h has: /* use arc4random on platforms that support it */ #ifdef MP_USE_ALT_RAND #define MP_GEN_RANDOM() arc4random() #else #define MP_GEN_RANDOM() rand() #endif #define MP_DIGIT_BIT DIGIT_BIT #define MP_MASK ((((mp_digit)1)<<((mp_digit)DIGIT_BIT))-((mp_digit)1)) #define MP_DIGIT_MAX MP_MASK and #ifdef MP_31BIT /* this is an extension that uses 31-bit digits */ #define DIGIT_BIT 31 #else /* default case is 28-bit digits, defines MP_28BIT as a handy macro to test */ #define DIGIT_BIT 28 #define MP_28BIT #endif Which I think means that it's either using 28 or 31 bit "digits". IIRC rand() on Win32 only returns 15 bit values. Most *nix systems return 31 bit values. ANSI C only mandates 15 bit as a minimum. If so, this third-party code is buggy. But if that's true, why on Earth has no-one else hit this before? Nicholas Clark
