1 /* GStreamer

     2  * Copyright (C) 2008 Sebastian Dröge <sebastian.droege@collabora.co.uk>

     3  *

     4  * gstfastrandom.h: Fast, bad PNRG

     5  *

     6  * This library is free software; you can redistribute it and/or

     7  * modify it under the terms of the GNU Library General Public

     8  * License as published by the Free Software Foundation; either

     9  * version 2 of the License, or (at your option) any later version.

    10  *

    11  * This library is distributed in the hope that it will be useful,

    12  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    14  * Library General Public License for more details.

    15  *

    16  * You should have received a copy of the GNU Library General Public

    17  * License along with this library; if not, write to the

    18  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,

    19  * Boston, MA 02111-1307, USA.

    20  */

    21 

    22 #include <glib.h>

    23 

    24 #ifndef __GST_FAST_RANDOM__

    25 #define __GST_FAST_RANDOM__

    26 

    27 /* transform [0..2^32] -> [0..1] */

    28 #define GST_RAND_DOUBLE_TRANSFORM 2.3283064365386962890625e-10

    29 

    30 /* This is the base function, implementing a linear congruential generator

    31  * and returning a pseudo random number between 0 and 2^32 - 1.

    32  */

    33 static inline guint32

    34 gst_fast_random_uint32 ()

    35 {

    36   static guint32 state = 0xdeadbeef;

    37 

    38   return (state = state * 1103515245 + 12345);

    39 }

    40 

    41 static inline guint32

    42 gst_fast_random_uint32_range (gint32 start, gint32 end)

    43 {

    44   guint64 tmp = gst_fast_random_uint32 ();

    45 

    46   tmp = (tmp * (end - start)) / G_MAXUINT32 + start;

    47 

    48   return (guint32) tmp;

    49 }

    50 

    51 static inline gint32

    52 gst_fast_random_int32 (void)

    53 {

    54   return (gint32) gst_fast_random_uint32 ();

    55 }

    56 

    57 static inline gint32

    58 gst_fast_random_int32_range (gint32 start, gint32 end)

    59 {

    60   gint64 tmp = gst_fast_random_uint32 ();

    61 

    62   tmp = (tmp * (end - start)) / G_MAXUINT32 + start;

    63 

    64   return (gint32) tmp;

    65 }

    66 

    67 static inline gdouble

    68 gst_fast_random_double (void)

    69 {

    70   gdouble ret;

    71 

    72   ret = gst_fast_random_uint32 () * GST_RAND_DOUBLE_TRANSFORM;

    73   ret = (ret + gst_fast_random_uint32 ()) * GST_RAND_DOUBLE_TRANSFORM;

    74 

    75   if (ret >= 1.0)

    76     return gst_fast_random_double ();

    77 

    78   return ret;

    79 }

    80 

    81 static inline gdouble

    82 gst_fast_random_double_range (gdouble start, gdouble end)

    83 {

    84   return gst_fast_random_double () * (end - start) + start;

    85 }

    86 

    87 #undef GST_RAND_DOUBLE_TRANSFORM

    88 

    89 #endif /* __GST_FAST_RANDOM__ */

    90