1DRAND48(3) Linux Programmer's Manual DRAND48(3)
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6 drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48,
7 lcong48 - generate uniformly distributed pseudo-random numbers
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10 #include <stdlib.h>
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12 double drand48(void);
13 double erand48(unsigned short xsubi[3]);
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15 long lrand48(void);
16 long nrand48(unsigned short xsubi[3]);
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18 long mrand48(void);
19 long jrand48(unsigned short xsubi[3]);
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21 void srand48(long seedval);
22 unsigned short *seed48(unsigned short seed16v[3]);
23 void lcong48(unsigned short param[7]);
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25 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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27 All functions shown above:
28 _XOPEN_SOURCE
29 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
30 || /* Glibc <= 2.19: */ _SVID_SOURCE
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33 These functions generate pseudo-random numbers using the linear congru‐
34 ential algorithm and 48-bit integer arithmetic.
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36 The drand48() and erand48() functions return nonnegative double-preci‐
37 sion floating-point values uniformly distributed over the interval
38 [0.0, 1.0).
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40 The lrand48() and nrand48() functions return nonnegative long integers
41 uniformly distributed over the interval [0, 2^31).
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43 The mrand48() and jrand48() functions return signed long integers uni‐
44 formly distributed over the interval [-2^31, 2^31).
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46 The srand48(), seed48(), and lcong48() functions are initialization
47 functions, one of which should be called before using drand48(),
48 lrand48(), or mrand48(). The functions erand48(), nrand48(), and
49 jrand48() do not require an initialization function to be called first.
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51 All the functions work by generating a sequence of 48-bit integers, Xi,
52 according to the linear congruential formula:
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54 Xn+1 = (aXn + c) mod m, where n >= 0
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56 The parameter m = 2^48, hence 48-bit integer arithmetic is performed.
57 Unless lcong48() is called, a and c are given by:
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59 a = 0x5DEECE66D
60 c = 0xB
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62 The value returned by any of the functions drand48(), erand48(),
63 lrand48(), nrand48(), mrand48(), or jrand48() is computed by first gen‐
64 erating the next 48-bit Xi in the sequence. Then the appropriate num‐
65 ber of bits, according to the type of data item to be returned, is
66 copied from the high-order bits of Xi and transformed into the returned
67 value.
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69 The functions drand48(), lrand48(), and mrand48() store the last 48-bit
70 Xi generated in an internal buffer. The functions erand48(),
71 nrand48(), and jrand48() require the calling program to provide storage
72 for the successive Xi values in the array argument xsubi. The func‐
73 tions are initialized by placing the initial value of Xi into the array
74 before calling the function for the first time.
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76 The initializer function srand48() sets the high order 32-bits of Xi to
77 the argument seedval. The low order 16-bits are set to the arbitrary
78 value 0x330E.
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80 The initializer function seed48() sets the value of Xi to the 48-bit
81 value specified in the array argument seed16v. The previous value of
82 Xi is copied into an internal buffer and a pointer to this buffer is
83 returned by seed48().
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85 The initialization function lcong48() allows the user to specify ini‐
86 tial values for Xi, a, and c. Array argument elements param[0-2] spec‐
87 ify Xi, param[3-5] specify a, and param[6] specifies c. After
88 lcong48() has been called, a subsequent call to either srand48() or
89 seed48() will restore the standard values of a and c.
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92 For an explanation of the terms used in this section, see at‐
93 tributes(7).
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95 ┌───────────────────────────────────────┬───────────────┬──────────────┐
96 │Interface │ Attribute │ Value │
97 ├───────────────────────────────────────┼───────────────┼──────────────┤
98 │drand48(), erand48(), lrand48(), │ Thread safety │ MT-Unsafe │
99 │nrand48(), mrand48(), jrand48(), │ │ race:drand48 │
100 │srand48(), seed48(), lcong48() │ │ │
101 └───────────────────────────────────────┴───────────────┴──────────────┘
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103 The above functions record global state information for the random num‐
104 ber generator, so they are not thread-safe.
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107 POSIX.1-2001, POSIX.1-2008, SVr4.
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110 rand(3), random(3)
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113 This page is part of release 5.13 of the Linux man-pages project. A
114 description of the project, information about reporting bugs, and the
115 latest version of this page, can be found at
116 https://www.kernel.org/doc/man-pages/.
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120 2021-03-22 DRAND48(3)