ceph/src/civetweb/src/third_party/duktape-1.8.0/src-separate/duk_util_tinyrandom.c

   1 /*
   2  *  A tiny random number generator.
   3  *
   4  *  Currently used for Math.random().
   5  *
   6  *  http://www.woodmann.com/forum/archive/index.php/t-3100.html
   7  */
   8
   9 #include "duk_internal.h"
  10
  11 #define DUK__UPDATE_RND(rnd) do { \
  12                 (rnd) += ((rnd) * (rnd)) | 0x05; \
  13                 (rnd) = ((rnd) & 0xffffffffU);       /* if duk_uint32_t is exactly 32 bits, this is a NOP */ \
  14         } while (0)
  15
  16 #define DUK__RND_BIT(rnd)  ((rnd) >> 31)  /* only use the highest bit */
  17
  18 DUK_INTERNAL duk_uint32_t duk_util_tinyrandom_get_bits(duk_hthread *thr, duk_small_int_t n) {
  19         duk_small_int_t i;
  20         duk_uint32_t res = 0;
  21         duk_uint32_t rnd;
  22
  23         rnd = thr->heap->rnd_state;
  24
  25         for (i = 0; i < n; i++) {
  26                 DUK__UPDATE_RND(rnd);
  27                 res <<= 1;
  28                 res += DUK__RND_BIT(rnd);
  29         }
  30
  31         thr->heap->rnd_state = rnd;
  32
  33         return res;
  34 }
  35
  36 DUK_INTERNAL duk_double_t duk_util_tinyrandom_get_double(duk_hthread *thr) {
  37         duk_double_t t;
  38         duk_small_int_t n;
  39         duk_uint32_t rnd;
  40
  41         /*
  42          *  XXX: could make this a lot faster if we create the double memory
  43          *  representation directly.  Feasible easily (must be uniform random).
  44          */
  45
  46         rnd = thr->heap->rnd_state;
  47
  48         n = 53;  /* enough to cover the whole mantissa */
  49         t = 0.0;
  50
  51         do {
  52                 DUK__UPDATE_RND(rnd);
  53                 t += DUK__RND_BIT(rnd);
  54                 t /= 2.0;
  55         } while (--n);
  56
  57         thr->heap->rnd_state = rnd;
  58
  59         DUK_ASSERT(t >= (duk_double_t) 0.0);
  60         DUK_ASSERT(t < (duk_double_t) 1.0);
  61
  62         return t;
  63 }