random.c

   1 /*
   2  * random.c: Internal random number generator, guaranteed to work
   3  * the same way on all platforms. Used when generating an initial
   4  * game state from a random game seed; required to ensure that game
   5  * seeds can be exchanged between versions of a puzzle compiled for
   6  * different platforms.
   7  *
   8  * The generator is based on SHA-1. This is almost certainly
   9  * overkill, but I had the SHA-1 code kicking around and it was
  10  * easier to reuse it than to do anything else!
  11  */
  12
  13 #include <assert.h>
  14 #include <string.h>
  15 #include <stdio.h>
  16
  17 #include "puzzles.h"
  18
  19 /* ----------------------------------------------------------------------
  20  * Core SHA algorithm: processes 16-word blocks into a message digest.
  21  */
  22
  23 #define rol(x,y) ( ((x) << (y)) | (((uint32)x) >> (32-y)) )
  24
  25 static void SHA_Core_Init(uint32 h[5])
  26 {
  27     h[0] = 0x67452301;
  28     h[1] = 0xefcdab89;
  29     h[2] = 0x98badcfe;
  30     h[3] = 0x10325476;
  31     h[4] = 0xc3d2e1f0;
  32 }
  33
  34 static void SHATransform(uint32 * digest, uint32 * block)
  35 {
  36     uint32 w[80];
  37     uint32 a, b, c, d, e;
  38     int t;
  39
  40     for (t = 0; t < 16; t++)
  41         w[t] = block[t];
  42
  43     for (t = 16; t < 80; t++) {
  44         uint32 tmp = w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16];
  45         w[t] = rol(tmp, 1);
  46     }
  47
  48     a = digest[0];
  49     b = digest[1];
  50     c = digest[2];
  51     d = digest[3];
  52     e = digest[4];
  53
  54     for (t = 0; t < 20; t++) {
  55         uint32 tmp =
  56             rol(a, 5) + ((b & c) | (d & ~b)) + e + w[t] + 0x5a827999;
  57         e = d;
  58         d = c;
  59         c = rol(b, 30);
  60         b = a;
  61         a = tmp;
  62     }
  63     for (t = 20; t < 40; t++) {
  64         uint32 tmp = rol(a, 5) + (b ^ c ^ d) + e + w[t] + 0x6ed9eba1;
  65         e = d;
  66         d = c;
  67         c = rol(b, 30);
  68         b = a;
  69         a = tmp;
  70     }
  71     for (t = 40; t < 60; t++) {
  72         uint32 tmp = rol(a,
  73                          5) + ((b & c) | (b & d) | (c & d)) + e + w[t] +
  74             0x8f1bbcdc;
  75         e = d;
  76         d = c;
  77         c = rol(b, 30);
  78         b = a;
  79         a = tmp;
  80     }
  81     for (t = 60; t < 80; t++) {
  82         uint32 tmp = rol(a, 5) + (b ^ c ^ d) + e + w[t] + 0xca62c1d6;
  83         e = d;
  84         d = c;
  85         c = rol(b, 30);
  86         b = a;
  87         a = tmp;
  88     }
  89
  90     digest[0] += a;
  91     digest[1] += b;
  92     digest[2] += c;
  93     digest[3] += d;
  94     digest[4] += e;
  95 }
  96
  97 /* ----------------------------------------------------------------------
  98  * Outer SHA algorithm: take an arbitrary length byte string,
  99  * convert it into 16-word blocks with the prescribed padding at
 100  * the end, and pass those blocks to the core SHA algorithm.
 101  */
 102
 103 void SHA_Init(SHA_State * s)
 104 {
 105     SHA_Core_Init(s->h);
 106     s->blkused = 0;
 107     s->lenhi = s->lenlo = 0;
 108 }
 109
 110 void SHA_Bytes(SHA_State * s, const void *p, int len)
 111 {
 112     unsigned char *q = (unsigned char *) p;
 113     uint32 wordblock[16];
 114     uint32 lenw = len;
 115     int i;
 116
 117     /*
 118      * Update the length field.
 119      */
 120     s->lenlo += lenw;
 121     s->lenhi += (s->lenlo < lenw);
 122
 123     if (s->blkused && s->blkused + len < 64) {
 124         /*
 125          * Trivial case: just add to the block.
 126          */
 127         memcpy(s->block + s->blkused, q, len);
 128         s->blkused += len;
 129     } else {
 130         /*
 131          * We must complete and process at least one block.
 132          */
 133         while (s->blkused + len >= 64) {
 134             memcpy(s->block + s->blkused, q, 64 - s->blkused);
 135             q += 64 - s->blkused;
 136             len -= 64 - s->blkused;
 137             /* Now process the block. Gather bytes big-endian into words */
 138             for (i = 0; i < 16; i++) {
 139                 wordblock[i] =
 140                     (((uint32) s->block[i * 4 + 0]) << 24) |
 141                     (((uint32) s->block[i * 4 + 1]) << 16) |
 142                     (((uint32) s->block[i * 4 + 2]) << 8) |
 143                     (((uint32) s->block[i * 4 + 3]) << 0);
 144             }
 145             SHATransform(s->h, wordblock);
 146             s->blkused = 0;
 147         }
 148         memcpy(s->block, q, len);
 149         s->blkused = len;
 150     }
 151 }
 152
 153 void SHA_Final(SHA_State * s, unsigned char *output)
 154 {
 155     int i;
 156     int pad;
 157     unsigned char c[64];
 158     uint32 lenhi, lenlo;
 159
 160     if (s->blkused >= 56)
 161         pad = 56 + 64 - s->blkused;
 162     else
 163         pad = 56 - s->blkused;
 164
 165     lenhi = (s->lenhi << 3) | (s->lenlo >> (32 - 3));
 166     lenlo = (s->lenlo << 3);
 167
 168     memset(c, 0, pad);
 169     c[0] = 0x80;
 170     SHA_Bytes(s, &c, pad);
 171
 172     c[0] = (unsigned char)((lenhi >> 24) & 0xFF);
 173     c[1] = (unsigned char)((lenhi >> 16) & 0xFF);
 174     c[2] = (unsigned char)((lenhi >> 8) & 0xFF);
 175     c[3] = (unsigned char)((lenhi >> 0) & 0xFF);
 176     c[4] = (unsigned char)((lenlo >> 24) & 0xFF);
 177     c[5] = (unsigned char)((lenlo >> 16) & 0xFF);
 178     c[6] = (unsigned char)((lenlo >> 8) & 0xFF);
 179     c[7] = (unsigned char)((lenlo >> 0) & 0xFF);
 180
 181     SHA_Bytes(s, &c, 8);
 182
 183     for (i = 0; i < 5; i++) {
 184         output[i * 4] = (unsigned char)((s->h[i] >> 24) & 0xFF);
 185         output[i * 4 + 1] = (unsigned char)((s->h[i] >> 16) & 0xFF);
 186         output[i * 4 + 2] = (unsigned char)((s->h[i] >> 8) & 0xFF);
 187         output[i * 4 + 3] = (unsigned char)((s->h[i]) & 0xFF);
 188     }
 189 }
 190
 191 void SHA_Simple(const void *p, int len, unsigned char *output)
 192 {
 193     SHA_State s;
 194
 195     SHA_Init(&s);
 196     SHA_Bytes(&s, p, len);
 197     SHA_Final(&s, output);
 198 }
 199
 200 /* ----------------------------------------------------------------------
 201  * The random number generator.
 202  */
 203
 204 struct random_state {
 205     unsigned char seedbuf[40];
 206     unsigned char databuf[20];
 207     int pos;
 208 };
 209
 210 random_state *random_new(const char *seed, int len)
 211 {
 212     random_state *state;
 213
 214     state = snew(random_state);
 215
 216     SHA_Simple(seed, len, state->seedbuf);
 217     SHA_Simple(state->seedbuf, 20, state->seedbuf + 20);
 218     SHA_Simple(state->seedbuf, 40, state->databuf);
 219     state->pos = 0;
 220
 221     return state;
 222 }
 223
 224 random_state *random_copy(random_state *tocopy)
 225 {
 226     random_state *result;
 227     result = snew(random_state);
 228     memcpy(result->seedbuf, tocopy->seedbuf, sizeof(result->seedbuf));
 229     memcpy(result->databuf, tocopy->databuf, sizeof(result->databuf));
 230     result->pos = tocopy->pos;
 231     return result;
 232 }
 233
 234 unsigned long random_bits(random_state *state, int bits)
 235 {
 236     unsigned long ret = 0;
 237     int n;
 238
 239     for (n = 0; n < bits; n += 8) {
 240         if (state->pos >= 20) {
 241             int i;
 242
 243             for (i = 0; i < 20; i++) {
 244                 if (state->seedbuf[i] != 0xFF) {
 245                     state->seedbuf[i]++;
 246                     break;
 247                 } else
 248                     state->seedbuf[i] = 0;
 249             }
 250             SHA_Simple(state->seedbuf, 40, state->databuf);
 251             state->pos = 0;
 252         }
 253         ret = (ret << 8) | state->databuf[state->pos++];
 254     }
 255
 256     /*
 257      * `(1 << bits) - 1' is not good enough, since if bits==32 on a
 258      * 32-bit machine, behaviour is undefined and Intel has a nasty
 259      * habit of shifting left by zero instead. We'll shift by
 260      * bits-1 and then separately shift by one.
 261      */
 262     ret &= (1 << (bits-1)) * 2 - 1;
 263     return ret;
 264 }
 265
 266 unsigned long random_upto(random_state *state, unsigned long limit)
 267 {
 268     int bits = 0;
 269     unsigned long max, divisor, data;
 270
 271     while ((limit >> bits) != 0)
 272         bits++;
 273
 274     bits += 3;
 275     assert(bits < 32);
 276
 277     max = 1L << bits;
 278     divisor = max / limit;
 279     max = limit * divisor;
 280
 281     do {
 282         data = random_bits(state, bits);
 283     } while (data >= max);
 284
 285     return data / divisor;
 286 }
 287
 288 void random_free(random_state *state)
 289 {
 290     sfree(state);
 291 }
 292
 293 char *random_state_encode(random_state *state)
 294 {
 295     char retbuf[256];
 296     int len = 0, i;
 297
 298     for (i = 0; i < lenof(state->seedbuf); i++)
 299         len += sprintf(retbuf+len, "%02x", state->seedbuf[i]);
 300     for (i = 0; i < lenof(state->databuf); i++)
 301         len += sprintf(retbuf+len, "%02x", state->databuf[i]);
 302     len += sprintf(retbuf+len, "%02x", state->pos);
 303
 304     return dupstr(retbuf);
 305 }
 306
 307 random_state *random_state_decode(const char *input)
 308 {
 309     random_state *state;
 310     int pos, byte, digits;
 311
 312     state = snew(random_state);
 313
 314     memset(state->seedbuf, 0, sizeof(state->seedbuf));
 315     memset(state->databuf, 0, sizeof(state->databuf));
 316     state->pos = 0;
 317
 318     byte = digits = 0;
 319     pos = 0;
 320     while (*input) {
 321         int v = *input++;
 322
 323         if (v >= '0' && v <= '9')
 324             v = v - '0';
 325         else if (v >= 'A' && v <= 'F')
 326             v = v - 'A' + 10;
 327         else if (v >= 'a' && v <= 'f')
 328             v = v - 'a' + 10;
 329         else
 330             v = 0;
 331
 332         byte = (byte << 4) | v;
 333         digits++;
 334
 335         if (digits == 2) {
 336             /*
 337              * We have a byte. Put it somewhere.
 338              */
 339             if (pos < lenof(state->seedbuf))
 340                 state->seedbuf[pos++] = byte;
 341             else if (pos < lenof(state->seedbuf) + lenof(state->databuf))
 342                 state->databuf[pos++ - lenof(state->seedbuf)] = byte;
 343             else if (pos == lenof(state->seedbuf) + lenof(state->databuf) &&
 344                      byte <= lenof(state->databuf))
 345                 state->pos = byte;
 346             byte = digits = 0;
 347         }
 348     }
 349
 350     return state;
 351 }