Updated: 14 Aug 2002

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#include <stdlib.h>

**long random**(**void**);

**void srandom**(**unsigned int ***seed*);

**char *initstate**(**unsigned int ***seed*, **char ****state*, **size_t ***size*);

**char *setstate**(**const char ****state*);

The **random()** function uses a nonlinear additive feedback random-number generator employing a default
state array size of 31 long integers to return successive pseudo-random numbers in the range from 0 to 2
**31

-1. The period of this random-number generator is approximately 16 x (2
**31

-1). The size of the state array determines the period
of the random-number generator. Increasing the state array size increases the period.

The **srandom()** function initializes the current state array using the value of *seed*.

The **random()** and **srandom()** functions have (almost) the same calling sequence and initialization properties as **rand()** and **srand()** (see **rand**(3C)). The difference is that **rand**(3C) produces a much less random sequence---in fact, the low dozen bits generated by rand go through a cyclic pattern. All
the bits generated by **random()** are usable.

The algorithm from **rand()** is used by **srandom()** to generate the 31 state integers. Because of this, different **srandom()** seeds often produce, within an offset, the same sequence of low order bits from **random()**. If low order
bits are used directly, **random()** should be initialized with **setstate()** using high quality random values.

Unlike **srand()**, **srandom()** does not return the old seed because the amount of state information used is much more than a single word. Two other routines are provided to deal with restarting/changing random number generators. With 256 bytes of state information,
the period of the random-number generator is greater than 2
**69
, which should be sufficient for most purposes.

Like **rand**(3C), **random()** produces by default a sequence of numbers that can be duplicated by calling **srandom()** with 1 as the seed.

The **initstate()** and **setstate()** functions handle restarting and changing random-number generators. The **initstate()** function allows a state array, pointed to by the *state* argument, to be initialized for future use. The **size** argument, which specifies the size in bytes of the state array, is used by **initstate()** to decide what type of random-number generator to use; the larger the state array, the more random the numbers. Values for the amount of state information are 8, 32, 64, 128, and 256
bytes. Other values greater than 8 bytes are rounded down to the nearest one of these values. For values smaller than 8, **random()** uses a simple linear congruential random number generator. The *seed* argument specifies a starting point for the random-number sequence
and provides for restarting at the same point. The **initstate()** function returns a pointer to the previous state information array.

If **initstate()** has not been called, then **random()** behaves as though **initstate()** had been called with *seed*=1 and *size*=128.

If **initstate()** is called with *size*<8, then **random()** uses a simple linear congruential random number generator.

Once a state has been initialized, **setstate()** allows switching between state arrays. The array defined by the *state* argument is used for further random-number generation until **initstate()** is called or **setstate()** is called
again. The **setstate()** function returns a pointer to the previous state array.

The **random()** function returns the generated pseudo-random number.

The **srandom()** function returns no value.

Upon successful completion, **initstate()** and **setstate()** return a pointer to the previous state array. Otherwise, a null pointer is returned.

After initialization, a state array can be restarted at a different point in one of two ways:

•
The **initstate()** function can be used, with the desired seed, state array, and size of the array.

•
The **setstate()** function, with the desired state, can be used, followed by **srandom()** with the desired seed. The advantage of using both of these functions is that the size of the state array does not have to be saved once it is initialized.

**Example 1: Initialize an array.**

The following example demonstrates the use of **initstate()** to intialize an array. It also demonstrates how to initialize an array and pass it to **setstate()**.

# include <stdlib.h> static unsigned int state0[32]; static unsigned int state1[32] = { 3, 0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342, 0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd, 0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86, 0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7, 0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc, 0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb, 0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b, 0x27fb47b9 }; main() { unsigned seed; int n; seed = 1; n = 128; (void)initstate(seed, (char *)state0, n); printf("random() = %d0\n", random()); (void)setstate((char *)state1); printf("random() = %d0\n", random()); }

See **attributes**(5) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | See NOTES below. |

**drand48**(3C), **rand**(3C), **attributes**(5), **standards**(5)

The **random()** and **srandom()** functions are unsafe in multithreaded applications.

Use of these functions in multithreaded applications is unsupported.

For **initstate()** and **setstate()**, the *state* argument must be aligned on an **int** boundary.

Newer and better performing random number generators such as **addrans()** and **lcrans()** are available with the SUNWspro package.

- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- ERRORS
- USAGE
- EXAMPLES
- ATTRIBUTES
- SEE ALSO
- NOTES

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Time: 02:37:25 GMT, October 02, 2010