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1 perry 1 !!NAME
2 JohnMcPherson 2 drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 - generate uniformly distributed pseudo-random numbers
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4 !!SYNOPSIS
5
2 JohnMcPherson 6 __#include <stdlib.h>__
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2 JohnMcPherson 8 __double drand48(void);__
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2 JohnMcPherson 10 __double erand48(unsigned short __ ''xsubi'' __[[3]);__
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2 JohnMcPherson 12 __long int lrand48(void);__
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2 JohnMcPherson 14 __long int nrand48(unsigned short __ ''xsubi'' __[[3]);__
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2 JohnMcPherson 16 __long int mrand48(void);__
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2 JohnMcPherson 18 __long int jrand48(unsigned short __ ''xsubi'' __[[3]);__
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2 JohnMcPherson 20 __void srand48(long int __ ''seedval'' __);__
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2 JohnMcPherson 22 __unsigned short *seed48(unsigned short __ ''seed16v'' __[[3]);__
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2 JohnMcPherson 24 __void lcong48(unsigned short __ ''param'' __[[7]);__
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26
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2 JohnMcPherson 28 !!DESCRIPTION
29 These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arithmetic.
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2 JohnMcPherson 31 The __drand48()__ and __erand48()__ functions return non-negative double-precision floating-point values uniformly distributed between [[0.0, 1.0).
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2 JohnMcPherson 33 The __lrand48()__ and __nrand48()__ functions return non-negative long integers uniformly distributed between 0 and 2^31.
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2 JohnMcPherson 35 The __mrand48()__ and __jrand48()__ functions return signed long integers uniformly distributed between -2^31 and 2^31.
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2 JohnMcPherson 37 The __srand48()__, __seed48()__ and __lcong48()__ functions are initialization functions, one of which should be called before using __drand48()__, __lrand48()__ or __mrand48()__. The functions __erand48()__, __nrand48()__ and __jrand48()__ do not require an initialization function to be called first.
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2 JohnMcPherson 39 All the functions work by generating a sequence of 48-bit integers, ''Xi'', according to the linear congruential formula:
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2 JohnMcPherson 41 __Xn+1 = (aXn + c) mod m, where n >= 0__
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2 JohnMcPherson 43 The parameter ''m'' = 2^48, hence 48-bit integer arithmetic is performed. Unless __lcong48()__ is called, ''a'' and ''c'' are given by:
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2 JohnMcPherson 45 __a = 0x5DEECE66D__
46 __c = 0xB__
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2 JohnMcPherson 48 The value returned by any of the functions __drand48()__, __erand48()__, __lrand48()__, __nrand48()__, __mrand48()__ or __jrand48()__ is computed by first generating the next 48-bit ''Xi'' in the sequence. Then the appropriate number of bits, according to the type of data item to be returned, is copied from the high-order bits of ''Xi'' and transformed into the returned value.
1 perry 49
2 JohnMcPherson 50 The functions __drand48()__, __lrand48()__ and __mrand48()__ store the last 48-bit ''Xi'' generated in an internal buffer. The functions __erand48()__, __nrand48()__ and __jrand48()__ require the calling program to provide storage for the successive ''Xi'' values in the array argument ''xsubi''. The functions are initialized by placing the initial value of ''Xi'' into the array before calling the function for the first time.
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2 JohnMcPherson 52 The initializer function __srand48()__ sets the high order 32-bits of ''Xi'' to the argument ''seedval''. The low order 16-bits are set to the arbitrary value 0x330E.
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2 JohnMcPherson 54 The initializer function __seed48()__ sets the value of ''Xi'' to the 48-bit value specified in the array argument ''seed16v''. The previous value of ''Xi'' is copied into an internal buffer and a pointer to this buffer is returned by __seed48()__.
55
56 The initialization function __lcong48()__ allows the user to specify initial values for ''Xi'', ''a'' and ''c''. Array argument elements ''param[[0-2]'' specify ''Xi'', ''param[[3-5]'' specify ''a'', and ''param[[6]'' specifies ''c''. After __lcong48()__ has been called, a subsequent call to either __srand48()__ or __seed48()__ will restore the standard values of ''a'' and ''c''.
1 perry 57
58 !!CONFORMING TO
2 JohnMcPherson 59 SVID 3
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61 !!NOTES
2 JohnMcPherson 62 These functions are declared obsolete by SVID 3, which states that rand(3) should be used instead.
1 perry 63
64 !!SEE ALSO
65 rand(3), random(3)
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