Random Number Tables

A supply of fast pseudo-random numbers from table in bn/rand.c. The values are in the open interval (i.e. exclusive) of 0.0 to 1.0 range with a period of 4096. More...

Collaboration diagram for Random Number Tables:

Files
file	rand.h

Macros
#define	BN_RAND_TABSIZE   4096
#define	BN_RAND_TABMASK   0xfff
#define	BN_RANDSEED(_i, _seed)   _i = ((unsigned)_seed) % BN_RAND_TABSIZE
#define	BN_RANDOM(_i)   bn_rand_table[ _i = (_i+1) % BN_RAND_TABSIZE ]
#define	BN_RANDHALF(_i)   (bn_rand_table[ _i = (_i+1) % BN_RAND_TABSIZE ]-0.5)
#define	BN_RANDHALF_INIT(_p)   _p = bn_rand_table
#define	BN_RANDHALFTABSIZE   16535
#define	bn_rand_half(_p)
#define	bn_rand_init(_p, _seed)
#define	bn_rand0to1(_q)   (bn_rand_half(_q)+0.5)
#define	BN_SINTABSIZE   2048
#define	bn_tab_sin(_a)

Functions
void	bn_mathtab_constant (void)
	For benchmarking purposes, make the random number table predictable. Setting to all zeros keeps dithered values at their original values. More...
void	bn_rand_sph_sample (point_t sample, const point_t center, const fastf_t radius)
	Generate a sample point on a sphere per Marsaglia (1972). More...

Variables
const float	bn_rand_table [BN_RAND_TABSIZE]
int	bn_randhalftabsize
float	bn_rand_halftab [BN_RANDHALFTABSIZE]
const float	bn_sin_table [BN_SINTABSIZE]

Detailed Description

A supply of fast pseudo-random numbers from table in bn/rand.c. The values are in the open interval (i.e. exclusive) of 0.0 to 1.0 range with a period of 4096.

Usage:

unsigned idx;
float f;
 
BN_RANDSEED(idx, integer_seed);
 
while (NEED_MORE_RAND_NUMBERS) {
f = BN_RANDOM(idx);
}

Note that the values from bn_rand_half() become all 0.0 when the benchmark flag is set (bn_rand_halftab is set to all 0's). The numbers from bn_rand_table do not change, because the procedural noise would cease to exist.

Macro Definition Documentation

BN_RAND_TABSIZE

#define BN_RAND_TABSIZE   4096

Definition at line 63 of file rand.h.

BN_RAND_TABMASK

#define BN_RAND_TABMASK   0xfff

Definition at line 64 of file rand.h.

BN_RANDSEED

#define BN_RANDSEED	(		_i,
			_seed
	)		_i = ((unsigned)_seed) % BN_RAND_TABSIZE

Definition at line 65 of file rand.h.

BN_RANDOM

#define BN_RANDOM

(

_i

)

bn_rand_table[ _i = (_i+1) % BN_RAND_TABSIZE ]

BN_RANDOM always gives numbers between the open interval 0.0 to 1.0

Definition at line 78 of file rand.h.

BN_RANDHALF

#define BN_RANDHALF

(

_i

)

(bn_rand_table[ _i = (_i+1) % BN_RAND_TABSIZE ]-0.5)

BN_RANDHALF always gives numbers between the open interval -0.5 and 0.5

Definition at line 81 of file rand.h.

BN_RANDHALF_INIT

#define BN_RANDHALF_INIT

(

_p

)

_p = bn_rand_table

Definition at line 82 of file rand.h.

BN_RANDHALFTABSIZE

#define BN_RANDHALFTABSIZE   16535

Powers of two give streaking

Definition at line 84 of file rand.h.

bn_rand_half

#define bn_rand_half

(

_p

)

Value:

    ((++(_p) >= &bn_rand_halftab[bn_randhalftabsize] || \
      (_p) < bn_rand_halftab) ? \
    *((_p) = bn_rand_halftab) : *(_p))

random numbers between the closed interval -0.5 to 0.5 inclusive, except when benchmark flag is set, when this becomes a constant 0.0

Parameters

_p	float pointer type initialized by bn_rand_init()

Definition at line 102 of file rand.h.

bn_rand_init

#define bn_rand_init	(		_p,
			_seed
	)

Value:

    (_p) = &bn_rand_halftab[ \
        (int)(\
            (bn_rand_halftab[(_seed)%bn_randhalftabsize] + 0.5) * \
            (bn_randhalftabsize-1)) ]

initialize the seed for the large random number table (halftab)

Parameters

_p	float pointer to be initialized, used for bn_rand0to1() and bn_rand_half()
_seed	Integer SEED for offset in the table.

Definition at line 115 of file rand.h.

bn_rand0to1

#define bn_rand0to1

(

_q

)

(bn_rand_half(_q)+0.5)

random numbers in the closed interval 0.0 to 1.0 range (inclusive) except when benchmarking, when this is always 0.5

Parameters

_q	float pointer type initialized by bn_rand_init()

Definition at line 128 of file rand.h.

BN_SINTABSIZE

#define BN_SINTABSIZE   2048

Definition at line 130 of file rand.h.

bn_tab_sin

#define bn_tab_sin

(

_a

)

Value:

                         (((_a) > 0) ? \
                         (bn_sin_table[(int)((0.5+ (_a)*(BN_SINTABSIZE / M_2PI)))&(BN_SINTABSIZE-1)]) :\
                         (-bn_sin_table[(int)((0.5- (_a)*(BN_SINTABSIZE / M_2PI)))&(BN_SINTABSIZE-1)]))

Definition at line 132 of file rand.h.

Function Documentation

bn_mathtab_constant()

void bn_mathtab_constant

(

void

)

For benchmarking purposes, make the random number table predictable. Setting to all zeros keeps dithered values at their original values.

bn_rand_sph_sample()

void bn_rand_sph_sample	(	point_t	sample,
		const point_t	center,
		const fastf_t	radius
	)

Generate a sample point on a sphere per Marsaglia (1972).

Note that bn_sph_sample and its internal routines do not initialize the randmt seed - the user should call bn_randmt_seed in their code if a variable seed is required.

Variable Documentation

bn_rand_table

const float bn_rand_table[BN_RAND_TABSIZE]

extern

This is our table of random numbers. Rather than calling drand48() or random() or rand() we just pick numbers out of this table. This table has 4096 unique entries with floating point values ranging from the open interval (i.e. exclusive) 0.0 to 1.0 range.

There are convenience macros for access in the bn.h header.

bn_randhalftabsize

int bn_randhalftabsize

extern

bn_rand_halftab

float bn_rand_halftab[BN_RANDHALFTABSIZE]

extern

The actual table of random floating point numbers with values in the closed interval (i.e. inclusive) -0.5 to +0.5 range.

For benchmarking purposes, this table is zeroed.

bn_sin_table

const float bn_sin_table[BN_SINTABSIZE]

extern

table of floating point sine values in the closed (i.e. inclusive) interval -1.0 to 1.0 range.