Psuedo random generator with min max

Can't find my old thread on min max so asking again, I made this function which should be as close to random numbers getting on a computer without internet connection for that random.com or whatever it was, only I forgot how to use the 1 or 0 to produce a larger (or smaller) number within a range.

Code:

long mcc_rnd( time_t *ctx, long min, long max ) { /* With bit unitialised it should be much harder to predict if 1 or 0 will recieved */ time_t bit, seed = time(NULL); long val; if ( ctx ) bit = *ctx; if ( !bit ) bit = 1; val = (seed & bit) ? 1 : 0; bit <<= 1; if ( ctx ) *ctx = bit; if ( min > max ) min = max; if ( min != max ) return val ? min; if ( max ) return val ? max : 0; }

Would appreciate being reminded of how to do so.

After a google search I found a copy of what I used (forgot I had put one in the mitsy code) but that wound up crashing so now I went with something different:

Code:

typedef clock_t mcc_rnd_t; long mcc__rnd( mcc_rnd_t *ctx, long min, long max ) { /* With bit unitialised it should be much harder to predict * if 1 or 0 will be recieved */ mcc_rnd_t bit, seed = clock(); long val; if ( ctx ) bit = *ctx; if ( !bit || bit > seed ) bit = 1; val = (seed & bit) ? 1 : 0; bit <<= 1; if ( ctx ) *ctx = bit; if ( min > max ) min = max; if ( min != max ) { val *= bit; if ( val > max ) val = max; val -= min; return ( val < min ) ? min : val; } return val ? max : min; } #define mcc_rnd( ctx ) mcc__rnd( ctx, LONG_MIN, LONG_MAX )

Not as flexibile as I'd like but it'll do, any suggestions for more flexible results than the below are welcome

Code:

gcc -Wall -o "bimath" "bimath.c" && "./bimath" num = 4, val = 0 num = 16, val = 8 num = 0, val = 32 num = 0, val = 128 num = 1024, val = 0 num = 4096, val = 0 num = 16384, val = 8192 num = 0, val = 0 num = 16, val = 0 num = 0, val = 0 num = 256, val = 128 num = 1024, val = 0 num = 4096, val = 0 num = 16384, val = 8192 num = 4, val = 0 num = 16, val = 0 num = 64, val = 0 Compilation finished successfully.

And yes those results do change upon every run of the test code

Managed to make it a bit more random:

Code:

long mcc__rnd( mcc_rnd_t *ctx, long min, long max ) { /* With bit unitialised it should be much harder to predict * if 1 or 0 will be recieved */ mcc_rnd_t bit = 1, seed = clock(), mov = 0; long val; if ( ctx ) mov = *ctx; bit <<= mov++; if ( !bit || bit > seed ) { bit = 1; mov = 0; } val = (seed & bit) ? 1 : 0; bit <<= 1; if ( ctx ) *ctx = mov; if ( min > max ) min = max; if ( min != max ) { bit = ~((~0u) << mov); val *= (clock() & bit); if ( val > max ) val = max; val -= (min >= 0) ? min : -min; return ( val < min ) ? min : val; } return val ? max : min; }

Code:

gcc -Wall -o "bimath" "bimath.c" && "./bimath" num = 0, val = 0 num = 7, val = 1 num = 0, val = 0 num = 0, val = 58 num = 335, val = 0 num = 1378, val = 0 num = 0, val = 0 num = 0, val = 9604 num = 0, val = 0 num = 9, val = 7 num = 55, val = 21 num = 198, val = 67 num = 0, val = 465 num = 0, val = 1504 num = 9746, val = 0 num = 1, val = 0 num = 6, val = 0 Compilation finished successfully.

This is the closest to unpredictable as I can get it, while one can predict to an extent what range a number will fall in, those numbers can be wildly different in magnitude so trying to brute force in a real world scenario would be quite difficult I imagine.

Code:

long mcc__rnd( mcc_rnd_t *ctx, long min, long max ) { /* With bit unitialised it should be much harder to predict * if 1 or 0 will be recieved */ mcc_rnd_t bit = 1, seed = time(NULL), mov = 0; long val; if ( ctx ) mov = *ctx; bit <<= mov++; if ( !bit || bit > seed ) { bit = 1; mov = 0; } val = (seed & bit) ? 1 : 0; bit <<= 1; if ( ctx ) *ctx = mov; if ( min > max ) min = max; if ( min != max ) { seed *= clock(); bit = ~((~0u) << mov); val = (seed & bit); if ( val > max ) val = max; val -= (min >= 0) ? min : -min; return ( val < min ) ? min : val; } return val ? max : min; }

Code:

gcc -Wall -o "bimath" "bimath.c" && "./bimath" num = 1, val = 1 num = 12, val = 6 num = 17, val = 10 num = 168, val = 1 num = 102, val = 191 num = 2596, val = 726 num = 1083, val = 1172 num = 32249, val = 16043 num = 194309, val = 47031 num = 733379, val = 397596 num = 2288613, val = 1617047 num = 4556640, val = 6318009 num = 31990491, val = 197428 num = 141549053, val = 42647126 num = 339883433, val = 410515035 num = 0, val = 989835645 num = 2, val = 1 num = 14, val = 7 num = 51, val = 5 num = 10, val = 99 num = 122, val = 211 num = 2616, val = 657 num = 9295, val = 1192 num = 15974, val = 32536 num = 219261, val = 71983 num = 758331, val = 422548 num = 1559545, val = 1223762 num = 16410484, val = 1394637 num = 27067119, val = 28828488 num = 37723754, val = 73039555 num = 80173452, val = 115489253 num = 0, val = 780062943 num = 0, val = 0 num = 12, val = 6 num = 29, val = 15 num = 52, val = 13 num = 498, val = 75 num = 3170, val = 1211 num = 1657, val = 1746 num = 24720, val = 16617 num = 170574, val = 23296 num = 824510, val = 488727 num = 3010083, val = 577148 num = 15009850, val = 8382611 num = 25666485, val = 27427854 num = 237649712, val = 4530057 num = 583850667, val = 82295556 num = 0, val = 1233802879 num = 0, val = 1 num = 7, val = 0 num = 11, val = 29 num = 212, val = 45 num = 914, val = 68 num = 425, val = 514 num = 3097, val = 3275 num = 1495, val = 18057 num = 139246, val = 123040 num = 531038, val = 383760 num = 660686, val = 324903 num = 2510476, val = 4271845 num = 37914698, val = 6121635 num = 48571333, val = 83887134 num = 896327399, val = 430088089 num = 0, val = 1546279611 num = 1, val = 0 num = 15, val = 0 num = 58, val = 12 num = 227, val = 60 num = 577, val = 154 num = 2136, val = 177 num = 4630, val = 4808 num = 27871, val = 19768 num = 108189, val = 91983 num = 762125, val = 426342 num = 2276132, val = 1604566 num = 16037268, val = 2782790 num = 1109842, val = 2871211 num = 170731792, val = 107145666 num = 248497291, val = 319128893 num = 0, val = 898449503 num = 0, val = 0 num = 1, val = 2 num = 25, val = 4 num = 20, val = 109 num = 989, val = 54 num = 3398, val = 1439 num = 5892, val = 6070 num = 37058, val = 28955 num = 35634, val = 19428 num = 427426, val = 91643 num = 1941433, val = 1269867 num = 11508265, val = 4881026 num = 16880793, val = 18642162 num = 52285015, val = 87600816 num = 1062529134, val = 24103111 num = 0, val = 638739522 num = 3, val = 1 num = 15, val = 0 num = 26, val = 19 num = 236, val = 69 num = 871, val = 448 num = 1009, val = 1098 num = 7688, val = 7866 num = 55060, val = 6086 num = 77945, val = 4306 num = 92727, val = 281232 num = 2278300, val = 1606734 num = 14949633, val = 1695155 num = 46831117, val = 16799423 num = 188182742, val = 89280815 num = 590924347, val = 89369236 num = 0, val = 1099613355 num = 1, val = 0 num = 8, val = 1 num = 3, val = 21 num = 151, val = 112 num = 620, val = 197 num = 487, val = 576 num = 7433, val = 7522 num = 55161, val = 14290 num = 258448, val = 111170 num = 912384, val = 52313 num = 1754825, val = 1419042 num = 1171680, val = 4694418 num = 58637225, val = 26844162 num = 97564185, val = 132879986 num = 641568994, val = 140013883 num = 0, val = 1651813113 num = 3, val = 1 num = 11, val = 4 num = 6, val = 31 num = 218, val = 51 num = 853, val = 430 num = 4061, val = 54 num = 7000, val = 7178 num = 22138, val = 14035 num = 227120, val = 22409 num = 954695, val = 283129 num = 3181495, val = 748560 num = 1926784, val = 3688153 num = 7299312, val = 10822050 num = 14433209, val = 49749010 num = 523122217, val = 21567106 num = 0, val = 530256114 num = 3, val = 1 num = 0, val = 2 num = 50, val = 4 num = 134, val = 95 num = 513, val = 90 num = 3541, val = 1582 num = 6482, val = 6571 num = 29901, val = 21798 num = 234171, val = 29460 num = 225627, val = 414132 num = 691058, val = 19492 num = 10257890, val = 3630651 num = 34169003, val = 2375940 num = 108411764, val = 9509837 num = 885536228, val = 419296918 num = 0, val = 2037043551 num = 1, val = 0 num = 8, val = 2 num = 8, val = 1 num = 220, val = 53 num = 87, val = 176 num = 1067, val = 1156 num = 4006, val = 4095 num = 20305, val = 12202 num = 238374, val = 91096 num = 574428, val = 91367 Compilation finished successfully.

Why are you basing your rng() on time() and clock().

Which, depending on how often you call them, return
- the same as last time
- +1 from last time
- always some number greater than last time.

If you want crude-but-effective (for student homework), then use a LCG
Linear congruential generator - Wikipedia

If you want statistically sound, or cryptographically sound randomness, then that takes more work.

Quote:

Originally Posted by Salem

Why are you basing your rng() on time() and clock().

Which, depending on how often you call them, return
- the same as last time
- +1 from last time
- always some number greater than last time.

If you want crude-but-effective (for student homework), then use a LCG
Linear congruential generator - Wikipedia

If you want statistically sound, or cryptographically sound randomness, then that takes more work.

I wanted a thread safe version that was not easy to predict, I don't need impossible just hard enough that outside a test scenario it would be pretty hard to predict without first finding out when the function is called in the 1st place, for games this would be sufficient and for testing my bignum functions it is also sufficient (those numbers were actually passed through my checker function to see if they matched up, as you'll note by the lack of further output they did match).Since it always changes the seed the randomness can only be predicted after a few rounds of it being used. Feel free to stress test it though :)