hphp/zend/zend-math.h

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
   6    | Copyright (c) 1998-2010 Zend Technologies Ltd. (http://www.zend.com) |
   7    +----------------------------------------------------------------------+
   8    | This source file is subject to version 2.00 of the Zend license,     |
   9    | that is bundled with this package in the file LICENSE, and is        |
  10    | available through the world-wide-web at the following url:           |
  11    | http://www.zend.com/license/2_00.txt.                                |
  12    | If you did not receive a copy of the Zend license and are unable to  |
  13    | obtain it through the world-wide-web, please send a note to          |
  14    | license@zend.com so we can mail you a copy immediately.              |
  15    +----------------------------------------------------------------------+
  16 */
  17
  18 #ifndef incl_HPHP_ZEND_MATH_H_
  19 #define incl_HPHP_ZEND_MATH_H_
  20
  21 #include <cmath>
  22 #include <cstdint>
  23
  24 namespace HPHP {
  25 ///////////////////////////////////////////////////////////////////////////////
  26
  27 #define PHP_ROUND_HALF_UP 1
  28 #define PHP_ROUND_HALF_DOWN 2
  29 #define PHP_ROUND_HALF_EVEN 3
  30 #define PHP_ROUND_HALF_ODD 4
  31
  32 double php_math_round(double value, int places, int mode = PHP_ROUND_HALF_UP);
  33
  34 /* System Rand functions */
  35 #ifndef RAND_MAX
  36 #define RAND_MAX (1<<15)
  37 #endif
  38
  39 #define MT_RAND_MAX 0x7FFFFFFFLL
  40
  41 /*
  42  * A bit of tricky math here.  We want to avoid using a modulus because
  43  * that simply tosses the high-order bits and might skew the distribution
  44  * of random values over the range.  Instead we map the range directly.
  45  *
  46  * We need to map the range from 0...M evenly to the range a...b
  47  * Let n = the random number and n' = the mapped random number
  48  *
  49  * Then we have: n' = a + n(b-a)/M
  50  *
  51  * We have a problem here in that only n==M will get mapped to b which
  52  # means the chances of getting b is much much less than getting any of
  53  # the other values in the range.  We can fix this by increasing our range
  54  # artifically and using:
  55  #
  56  #               n' = a + n(b-a+1)/M
  57  *
  58  # Now we only have a problem if n==M which would cause us to produce a
  59  # number of b+1 which would be bad.  So we bump M up by one to make sure
  60  # this will never happen, and the final algorithm looks like this:
  61  #
  62  #               n' = a + n(b-a+1)/(M+1)
  63  *
  64  * -RL
  65  */
  66 #define RAND_RANGE(__n, __min, __max, __tmax) \
  67   (__n) = (__min) + (int64_t) ((double) ((double)(__max) - (__min) + 1.0) * \
  68                             ((__n) / ((__tmax) + 1.0)))
  69
  70 #define GENERATE_SEED() \
  71   (((long) (time(0) * getpid())) ^ ((long) (1000000.0 * math_combined_lcg())))
  72
  73
  74 ///////////////////////////////////////////////////////////////////////////////
  75
  76 void math_mt_srand(uint32_t seed);
  77 int64_t math_mt_rand(int64_t min = 0, int64_t max = RAND_MAX);
  78
  79 double math_combined_lcg();
  80 int64_t math_generate_seed();
  81
  82 /*
  83  * The zend rand bookkeeping gets initialized at thread startup, and gets
  84  * reseeded on its first use in a request.  This is done by wiping the 'seeded'
  85  * bit at the end of each request.
  86  */
  87 void zend_rand_init();
  88 void zend_rand_unseed();
  89
  90 ///////////////////////////////////////////////////////////////////////////////
  91 }
  92
  93 #endif // incl_HPHP_ZEND_MATH_H_