INITSTATE(3P)

🌸 PROLOG 🌸

okay so before literally anything else, bestie, real talk: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. 💀 so like. check first. always.

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✨ NAME ✨

initstate, random, setstate, srandom — pseudo-random number functions 🎲✨

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🎀 SYNOPSIS 🎀

#include <stdlib.h>

char *initstate(unsigned seed, char *state, size_t size);
long random(void);
char *setstate(char *state);
void srandom(unsigned seed);

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💖 DESCRIPTION 💖

okay so the random() function uses a non-linear additive feedback random-number generator (yes that's the whole name, slay) with a default state array size of 31 long integers, and it hands you back successive pseudo-random numbers in the range from 0 to 231-1. the period of this random-number generator is approximately 16 x (231-1). the size of the state array is what decides the period, so like — increase the state array size and the period increases too. it's giving growth mindset. 📈

with 256 bytes of state information, the period of the random-number generator is greater than 269. 🫶

like rand(), random() produces by default a sequence of numbers that can be duplicated by calling srandom() with 1 as the seed. so yeah, reproducible, iconic.

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

the initstate() and setstate() functions handle restarting and changing random-number generators. initstate() lets a state array — the one pointed to by the state argument — be initialized for future use. the size argument specifies the size in bytes of the state array, and initstate() uses it to decide what type of random-number generator to use; the larger the state array, the more random the numbers. the values for the amount of state information are 8, 32, 64, 128, and 256 bytes. other values greater than 8 bytes get rounded down to the nearest one of these values. if initstate() is called with 8≤size<32, then 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. and initstate() 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. default behavior era, honestly.

once a state has been initialized, setstate() lets you switch 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. and setstate() returns a pointer to the previous state array. 🦋

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🌟 RETURN VALUE 🌟

• if initstate() is called with size less than 8, it returns NULL. 🙈
• the random() function returns the generated pseudo-random number.
• the srandom() function does not return a value.
• upon successful completion, initstate() and setstate() return a pointer to the previous state array; otherwise, a null pointer is returned.

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💀 ERRORS 💀

no errors are defined. 💅

the following sections are informative.

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🍓 EXAMPLES 🍓

none.

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🌈 APPLICATION USAGE 🌈

once it's initialized, a state array can be restarted at a different point in one of two ways:

1. initstate() can be used, with the desired seed, state array, and size of the array.
2. setstate() can be used with the desired state, 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. lowkey efficient.

although some implementations of random() have written messages to standard error, such implementations do not conform to POSIX.1‐2017. so like. don't do that. 😭

issue 5 restored the historical behavior of this function.

threaded applications should use erand48(), nrand48(), or jrand48() instead of random() when an independent random number sequence in multiple threads is required. no sharing, besties, it's not cute.

these functions should be avoided whenever non-trivial requirements (including safety) have to be fulfilled. like genuinely. not a vibe, but a warning. 🚨

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🧚 RATIONALE 🧚

none.

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💜 FUTURE DIRECTIONS 💜

none.

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👑 SEE ALSO 👑

drand48(), rand()

The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

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🎀 COPYRIGHT 🎀

okay legal bestie moment, here's the whole thing, character for character:

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie — IEEE/The Open Group, 2017, INITSTATE(3P), periodt. 💅✨ go seed something. 🎲💖