From: Dale Weiler Date: Wed, 14 Aug 2013 06:22:32 +0000 (+0000) Subject: Remove my MT impl for PRNG, it's full of buffer overflows that I don't want to fix... X-Git-Tag: v0.3.0~24 X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=0a5353532b15fce7470f189824d252d49806bea6;p=xonotic%2Fgmqcc.git Remove my MT impl for PRNG, it's full of buffer overflows that I don't want to fix. Just fallback to using srand/rand --- diff --git a/util.c b/util.c index 32edbbd..7d6e034 100644 --- a/util.c +++ b/util.c @@ -409,173 +409,10 @@ int util_asprintf(char **ret, const char *fmt, ...) { #endif /*! _MSC_VER */ -/* - * Implementation of the Mersenne twister PRNG (pseudo random numer - * generator). Implementation of MT19937. Has a period of 2^19937-1 - * which is a Mersenne Prime (hence the name). - * - * Implemented from specification and original paper: - * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/ARTICLES/mt.pdf - * - * This code is placed in the public domain by me personally - * (Dale Weiler, a.k.a graphitemaster). - */ - -#define MT_SIZE 624 -#define MT_PERIOD 397 -#define MT_SPACE (MT_SIZE - MT_PERIOD) - -static uint32_t mt_state[MT_SIZE]; -static size_t mt_index = 0; - -static GMQCC_INLINE void mt_generate(void) { - /* - * The loop has been unrolled here: the original paper and implemenation - * Called for the following code: - * for (register unsigned i = 0; i < MT_SIZE; ++i) { - * register uint32_t load; - * load = (0x80000000 & mt_state[i]) // most significant 32nd bit - * load |= (0x7FFFFFFF & mt_state[(i + 1) % MT_SIZE]) // least significant 31nd bit - * - * mt_state[i] = mt_state[(i + MT_PERIOD) % MT_SIZE] ^ (load >> 1); - * - * if (load & 1) mt_state[i] ^= 0x9908B0DF; - * } - * - * This essentially is a waste: we have two modulus operations, and - * a branch that is executed every iteration from [0, MT_SIZE). - * - * Please see: http://www.quadibloc.com/crypto/co4814.htm for more - * information on how this clever trick works. - */ - static const uint32_t matrix[2] = { - 0x00000000, - 0x9908B0Df - }; - /* - * This register gives up a little more speed by instructing the compiler - * to force these into CPU registers (they're counters for indexing mt_state - * which we can force the compiler to generate prefetch instructions for) - */ - register uint32_t y; - register uint32_t i; - - /* - * Said loop has been unrolled for MT_SPACE (226 iterations), opposed - * to [0, MT_SIZE) (634 iterations). - */ - for (i = 0; i < MT_SPACE-1; ++i) { - y = (0x80000000 & mt_state[i]) | (0x7FFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i + MT_PERIOD] ^ (y >> 1) ^ matrix[y & 1]; - - i ++; /* loop unroll */ - - y = (0x80000000 & mt_state[i]) | (0x7FFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i + MT_PERIOD] ^ (y >> 1) ^ matrix[y & 1]; - } - - /* - * collapsing the walls unrolled (evenly dividing 396 [632-227 = 396 - * = 2*2*3*3*11]) - */ - i = MT_SPACE; - while (i < MT_SIZE-2) { - /* - * We expand this 11 times .. manually, no macros are required - * here. This all fits in the CPU cache. - */ - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - y = (0x80000000 & mt_state[i]) | (0x7FFFFFFF & mt_state[i + 1]); - mt_state[i] = mt_state[i - MT_SPACE] ^ (y >> 1) ^ matrix[y & 1]; - ++i; - } - - /* i = mt_state[623] */ - y = (0x80000000 & mt_state[MT_SIZE - 1]) | (0x7FFFFFFF & mt_state[MT_SIZE - 1]); - mt_state[MT_SIZE - 1] = mt_state[MT_PERIOD - 1] ^ (y >> 1) ^ matrix[y & 1]; -} void util_seed(uint32_t value) { - /* - * We seed the mt_state with a LCG (linear congruential generator) - * We're operating exactly on exactly m=32, so there is no need to - * use modulus. - * - * The multipler of choice is 0x6C07865, also knows as the Borosh- - * Niederreiter multipler used for modulus 2^32. More can be read - * about this in Knuth's TAOCP Volume 2, page 106. - * - * If you don't own TAOCP something is wrong with you :-) .. so I - * also provided a link to the original paper by Borosh and - * Niederreiter. It's called "Optional Multipliers for PRNG by The - * Linear Congruential Method" (1983). - * http://en.wikipedia.org/wiki/Linear_congruential_generator - * - * From said page, it says the following: - * "A common Mersenne twister implementation, interestingly enough - * used an LCG to generate seed data." - * - * Remarks: - * The data we're operating on is 32-bits for the mt_state array, so - * there is no masking required with 0xFFFFFFFF - */ - register size_t i; - - mt_state[0] = value; - for (i = 1; i < MT_SIZE; ++i) - mt_state[i] = 0x6C078965 * (mt_state[i - 1] ^ mt_state[i - 1] >> 30) + i; + srand((int)value); } - uint32_t util_rand() { - register uint32_t y; - - /* - * This is inlined with any sane compiler (I checked) - * for some reason though, SubC seems to be generating invalid - * code when it inlines this. - */ - if (!mt_index) - mt_generate(); - - y = mt_state[mt_index]; - - /* Standard tempering */ - y ^= y >> 11; /* +7 */ - y ^= y << 7 & 0x9D2C5680; /* +4 */ - y ^= y << 15 & 0xEFC60000; /* -4 */ - y ^= y >> 18; /* -7 */ - - if(++mt_index == MT_SIZE) - mt_index = 0; - - return y; + return rand(); }