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-rw-r--r--src/lib/libc/stdlib/rand48.345
1 files changed, 25 insertions, 20 deletions
diff --git a/src/lib/libc/stdlib/rand48.3 b/src/lib/libc/stdlib/rand48.3
index 5a772c9a8c..78cd0a7cd5 100644
--- a/src/lib/libc/stdlib/rand48.3
+++ b/src/lib/libc/stdlib/rand48.3
@@ -1,4 +1,4 @@
1\" Copyright (c) 1993 Martin Birgmeier 1.\" Copyright (c) 1993 Martin Birgmeier
2.\" All rights reserved. 2.\" All rights reserved.
3.\" 3.\"
4.\" You may redistribute unmodified or modified versions of this source 4.\" You may redistribute unmodified or modified versions of this source
@@ -9,7 +9,7 @@
9.\" of any kind. I shall in no event be liable for anything that happens 9.\" of any kind. I shall in no event be liable for anything that happens
10.\" to anyone/anything when using this software. 10.\" to anyone/anything when using this software.
11.\" 11.\"
12.\" $Id: rand48.3,v 1.1.1.1 1995/10/18 08:42:19 deraadt Exp $ 12.\" $OpenBSD: rand48.3,v 1.10 2003/06/01 19:27:27 jmc Exp $
13.\" 13.\"
14.Dd October 8, 1993 14.Dd October 8, 1993
15.Dt RAND48 3 15.Dt RAND48 3
@@ -24,10 +24,10 @@
24.Nm srand48 , 24.Nm srand48 ,
25.Nm seed48 , 25.Nm seed48 ,
26.Nm lcong48 26.Nm lcong48
27.Nd pseudo random number generators and initialization routines 27.Nd pseudo-random number generators and initialization routines
28.Sh SYNOPSIS 28.Sh SYNOPSIS
29.Fd #include <stdlib.h> 29.Fd #include <stdlib.h>
30.Ft double 30.Ft double
31.Fn drand48 void 31.Fn drand48 void
32.Ft double 32.Ft double
33.Fn erand48 "unsigned short xseed[3]" 33.Fn erand48 "unsigned short xseed[3]"
@@ -49,12 +49,13 @@
49The 49The
50.Fn rand48 50.Fn rand48
51family of functions generates pseudo-random numbers using a linear 51family of functions generates pseudo-random numbers using a linear
52congruential algorithm working on integers 48 bits in size. The 52congruential algorithm working on integers 48 bits in size.
53particular formula employed is 53The particular formula employed is
54r(n+1) = (a * r(n) + c) mod m 54r(n+1) = (a * r(n) + c) mod m
55where the default values are 55where the default values are
56for the multiplicand a = 0xfdeece66d = 25214903917 and 56for the multiplicand a = 0xfdeece66d = 25214903917 and
57the addend c = 0xb = 11. The modulus is always fixed at m = 2 ** 48. 57the addend c = 0xb = 11.
58The modulus is always fixed at m = 2 ** 48.
58r(n) is called the seed of the random number generator. 59r(n) is called the seed of the random number generator.
59.Pp 60.Pp
60For all the six generator routines described next, the first 61For all the six generator routines described next, the first
@@ -63,15 +64,17 @@ computational step is to perform a single iteration of the algorithm.
63.Fn drand48 64.Fn drand48
64and 65and
65.Fn erand48 66.Fn erand48
66return values of type double. The full 48 bits of r(n+1) are 67return values of type double.
68The full 48 bits of r(n+1) are
67loaded into the mantissa of the returned value, with the exponent set 69loaded into the mantissa of the returned value, with the exponent set
68such that the values produced lie in the interval [0.0, 1.0). 70such that the values produced lie in the interval [0.0, 1.0].
69.Pp 71.Pp
70.Fn lrand48 72.Fn lrand48
71and 73and
72.Fn nrand48 74.Fn nrand48
73return values of type long in the range 75return values of type long in the range
74[0, 2**31-1]. The high-order (31) bits of 76[0, 2**31-1].
77The high-order (31) bits of
75r(n+1) are loaded into the lower bits of the returned value, with 78r(n+1) are loaded into the lower bits of the returned value, with
76the topmost (sign) bit set to zero. 79the topmost (sign) bit set to zero.
77.Pp 80.Pp
@@ -79,14 +82,15 @@ the topmost (sign) bit set to zero.
79and 82and
80.Fn jrand48 83.Fn jrand48
81return values of type long in the range 84return values of type long in the range
82[-2**31, 2**31-1]. The high-order (32) bits of 85[-2**31, 2**31-1].
83r(n+1) are loaded into the returned value. 86The high-order (32) bits of r(n+1) are loaded into the returned value.
84.Pp 87.Pp
85.Fn drand48 , 88.Fn drand48 ,
86.Fn lrand48 , 89.Fn lrand48 ,
87and 90and
88.Fn mrand48 91.Fn mrand48
89use an internal buffer to store r(n). For these functions 92use an internal buffer to store r(n).
93For these functions
90the initial value of r(0) = 0x1234abcd330e = 20017429951246. 94the initial value of r(0) = 0x1234abcd330e = 20017429951246.
91.Pp 95.Pp
92On the other hand, 96On the other hand,
@@ -118,12 +122,12 @@ also initializes the internal buffer r(n) of
118and 122and
119.Fn mrand48 , 123.Fn mrand48 ,
120but here all 48 bits of the seed can be specified in an array of 3 shorts, 124but here all 48 bits of the seed can be specified in an array of 3 shorts,
121where the zeroth member specifies the lowest bits. Again, 125where the zeroth member specifies the lowest bits.
122the constant multiplicand and addend of the algorithm are 126Again, the constant multiplicand and addend of the algorithm are
123reset to the default values given above. 127reset to the default values given above.
124.Fn seed48 128.Fn seed48
125returns a pointer to an array of 3 shorts which contains the old seed. 129returns a pointer to an array of 3 shorts which contains the old seed.
126This array is statically allocated, thus its contents are lost after 130This array is statically allocated, so its contents are lost after
127each new call to 131each new call to
128.Fn seed48 . 132.Fn seed48 .
129.Pp 133.Pp
@@ -152,9 +156,10 @@ always also set the multiplicand and addend for any of the six
152generator calls. 156generator calls.
153.Pp 157.Pp
154For a more powerful random number generator, see 158For a more powerful random number generator, see
155.Xr random 3 159.Xr random 3 .
156.Sh AUTHOR
157Martin Birgmeier
158.Sh SEE ALSO 160.Sh SEE ALSO
161.Xr arc4random 3 ,
159.Xr rand 3 , 162.Xr rand 3 ,
160.Xr random 3 . 163.Xr random 3
164.Sh AUTHORS
165Martin Birgmeier