INITSTATE(3POSIX)

okay bestie, sit down, hydrate 🍓 — this is initstate(3POSIX) from the POSIX Programmer's Manual, and it's about the whole random-number squad: initstate, random, setstate, srandom. it's giving chaos, it's giving reproducibility, it's giving group chat at 2am. let's go 💅

🌸 PROLOG 🌸

so like, heads up first: this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ — bestie, consult the corresponding Linux manual page for the details on Linux behavior — or honestly, the interface may not be implemented on Linux at all. 🙈 no cap.

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✨ NAME ✨

initstate, random, setstate, srandom — pseudo-random number functions. it's giving random girl summer 🎲

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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 random() shall use a non-linear additive feedback random-number generator — say that five times fast — employing a default state array size of 31 long integers, and it returns successive pseudo-random numbers in the range from 0 to 231-1. yes queen, math. 👑

the period of this random-number generator is approximately 16 x (231-1). the size of the state array determines the period of the random-number generator. increasing the state array size shall increase the period. bigger array, longer period, periodt. 💅

with 256 bytes of state information, the period of the random-number generator shall be greater than 269. iconic.

like rand(), random() shall produce by default a sequence of numbers that can be duplicated by calling srandom() with 1 as the seed. so yes, same seed = same sequence, fr fr. reproducible bestie behaviour.

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

initstate() and setstate() 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, shall be 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. and if initstate() is called with 8≤size<32, then random() shall use a simple linear congruential random number generator. lowkey different engine, same vibe. the seed argument specifies a starting point for the random-number sequence and provides for restarting at the same point. the initstate() function shall return a pointer to the previous state information array.

if initstate() has not been called, then random() shall behave as though initstate() had been called with seed=1 and size=128. the default is doing the most, silently. 😭

once a state has been initialized, setstate() allows switching between state arrays. the array defined by the state argument shall be used for further random-number generation until initstate() is called or setstate() is called again. the setstate() function shall return a pointer to the previous state array. hot-swapping states? we love to see it. 🔥

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🎀 RETURN VALUE 🎀

• if initstate() is called with size less than 8, it shall return NULL. 🚫 not enough state bestie, sorry
• the random() function shall return the generated pseudo-random number. ✨
• the srandom() function shall not return a value. (it's giving void energy)
• upon successful completion, initstate() and setstate() shall return a pointer to the previous state array; otherwise, a null pointer shall be returned.

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💜 ERRORS 💜

no errors are defined. iconic, honestly.

the following sections are informative.

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🌈 EXAMPLES 🌈

none. 😭 not a single one. we move.

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🫶 APPLICATION USAGE 🫶

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

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

although some implementations of random() have written messages to standard error, such implementations do not conform to POSIX.1-2017. 🙅 not it.

issue 5 restored the historical behavior of this function. the ancestors said "put it back" and they put it back.

threaded applications should use erand48(), nrand48(), or jrand48() instead of random() when an independent random number sequence in multiple threads is required. seriously bestie, don't share random() across threads, it's not the moment.

and the big one:

these functions should be avoided whenever non-trivial requirements (including safety) have to be fulfilled. 💀 so like, do NOT build your security on this. no cap.

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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 💌

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 — brought to you by IEEE/The Open Group, 2017 🦋 mwah, stay random, stay seeded, and please seed with something better than 1 in production 💖✨