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Annotation of cci/usr/src/man/man3/random.3, revision 1.1

1.1     ! root        1: .TH RANDOM 3 "19 January 1983"
        !             2: .UC 4
        !             3: .SH NAME
        !             4: random, srandom, initstate, setstate \- better random number generator; routines for changing generators
        !             5: .SH SYNOPSIS
        !             6: .nf
        !             7: .B long  random()
        !             8: .PP
        !             9: .B srandom(seed)
        !            10: .B int  seed;
        !            11: .PP
        !            12: .B char  *initstate(seed, state, n)
        !            13: .B unsigned  seed;
        !            14: .B char  *state;
        !            15: .B int  n;
        !            16: .PP
        !            17: .B char  *setstate(state)
        !            18: .B char  *state;
        !            19: .fi
        !            20: .SH DESCRIPTION
        !            21: .PP
        !            22: .I Random
        !            23: uses a non-linear additive feedback random number generator employing a
        !            24: default table of size 31 long integers to return successive pseudo-random
        !            25: numbers in the range from 0 to 2\u\s731\s10\d\-1.  The period of this
        !            26: random number generator is very large, approximately 16*(2\u\s731\s10\d\-1).
        !            27: .PP
        !            28: .I Random/srandom
        !            29: have (almost) the same calling sequence and initialization properties as
        !            30: .I rand/srand.
        !            31: The difference is that
        !            32: .IR rand (3)
        !            33: produces a much less random sequence -- in fact, the low dozen bits
        !            34: generated by rand go through a cyclic pattern.  All the bits generated by
        !            35: .I random
        !            36: are usable.  For example, \*(lqrandom()&01\*(rq will produce a random binary
        !            37: value.
        !            38: .PP
        !            39: Unlike
        !            40: .IR srand ,
        !            41: .I srandom
        !            42: does not return the old seed; the reason for this is that the amount of
        !            43: state information used is much more than a single word.  (Two other
        !            44: routines are provided to deal with restarting/changing random
        !            45: number generators).  Like
        !            46: .IR rand (3),
        !            47: however,
        !            48: .I random
        !            49: will by default produce a sequence of numbers that can be duplicated
        !            50: by calling
        !            51: .I srandom
        !            52: with 
        !            53: .I 1
        !            54: as the seed.
        !            55: .PP
        !            56: The
        !            57: .I initstate
        !            58: routine allows a state array, passed in as an argument, to be initialized
        !            59: for future use.  The size of the state array (in bytes) is used by
        !            60: .I initstate
        !            61: to decide how sophisticated a random number generator it should use -- the
        !            62: more state, the better the random numbers will be.
        !            63: (Current "optimal" values for the amount of state information are
        !            64: 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
        !            65: the nearest known amount.  Using less than 8 bytes will cause an error).
        !            66: The seed for the initialization (which specifies a starting point for
        !            67: the random number sequence, and provides for restarting at the same
        !            68: point) is also an argument.
        !            69: .I Initstate
        !            70: returns a pointer to the previous state information array.
        !            71: .PP
        !            72: Once a state has been initialized, the
        !            73: .I setstate
        !            74: routine provides for rapid switching between states.
        !            75: .I Setstate returns a pointer to the previous state array; its
        !            76: argument state array is used for further random number generation
        !            77: until the next call to
        !            78: .I initstate
        !            79: or
        !            80: .I setstate.
        !            81: .PP
        !            82: Once a state array has been initialized, it may be restarted at a
        !            83: different point either by calling
        !            84: .I initstate
        !            85: (with the desired seed, the state array, and its size) or by calling
        !            86: both
        !            87: .I setstate
        !            88: (with the state array) and
        !            89: .I srandom
        !            90: (with the desired seed).
        !            91: The advantage of calling both
        !            92: .I setstate
        !            93: and
        !            94: .I srandom
        !            95: is that the size of the state array does not have to be remembered after
        !            96: it is initialized.
        !            97: .PP
        !            98: With 256 bytes of state information, the period of the random number
        !            99: generator is greater than 2\u\s769\s10\d, which should be sufficient for
        !           100: most purposes.
        !           101: .SH AUTHOR
        !           102: Earl T. Cohen
        !           103: .SH DIAGNOSTICS
        !           104: .PP
        !           105: If
        !           106: .I initstate
        !           107: is called with less than 8 bytes of state information, or if
        !           108: .I setstate
        !           109: detects that the state information has been garbled, error
        !           110: messages are printed on the standard error output.
        !           111: .SH "SEE ALSO"
        !           112: rand(3)
        !           113: .SH BUGS
        !           114: About 2/3 the speed of
        !           115: .IR rand (3C).

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