1 /* 2 * Copyright (c) 1993 Martin Birgmeier 3 * All rights reserved. 4 * 5 * You may redistribute unmodified or modified versions of this source 6 * code provided that the above copyright notice and this and the 7 * following conditions are retained. 8 * 9 * This software is provided ``as is'', and comes with no warranties 10 * of any kind. I shall in no event be liable for anything that happens 11 * to anyone/anything when using this software. 12 */ 13 14 /* 15 FUNCTION 16 <<rand48>>, <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>, <<mrand48>>, <<jrand48>>, <<srand48>>, <<seed48>>, <<lcong48>> ---pseudo random number generators and initialization routines 17 18 INDEX 19 rand48 20 INDEX 21 drand48 22 INDEX 23 erand48 24 INDEX 25 lrand48 26 INDEX 27 nrand48 28 INDEX 29 mrand48 30 INDEX 31 jrand48 32 INDEX 33 srand48 34 INDEX 35 seed48 36 INDEX 37 lcong48 38 39 ANSI_SYNOPSIS 40 #include <stdlib.h> 41 double drand48(void); 42 double erand48(unsigned short <[xseed]>[3]); 43 long lrand48(void); 44 long nrand48(unsigned short <[xseed]>[3]); 45 long mrand48(void); 46 long jrand48(unsigned short <[xseed]>[3]); 47 void srand48(long <[seed]>); 48 unsigned short *seed48(unsigned short <[xseed]>[3]); 49 void lcong48(unsigned short <[p]>[7]); 50 51 TRAD_SYNOPSIS 52 #include <stdlib.h> 53 double drand48(); 54 55 double erand48(<[xseed]>) 56 unsigned short <[xseed]>[3]; 57 58 long lrand48(); 59 60 long nrand48(<[xseed]>) 61 unsigned short <[xseed]>[3]; 62 63 long mrand48(); 64 65 long jrand48(<[xseed]>) 66 unsigned short <[xseed]>[3]; 67 68 void srand48(<[seed]>) 69 long <[seed]>; 70 71 unsigned short *seed48(<[xseed]>) 72 unsigned short <[xseed]>[3]; 73 74 void lcong48(<[p]>) 75 unsigned short <[p]>[7]; 76 77 DESCRIPTION 78 The <<rand48>> family of functions generates pseudo-random numbers 79 using a linear congruential algorithm working on integers 48 bits in size. 80 The particular formula employed is 81 r(n+1) = (a * r(n) + c) mod m 82 where the default values are 83 for the multiplicand a = 0xfdeece66d = 25214903917 and 84 the addend c = 0xb = 11. The modulo is always fixed at m = 2 ** 48. 85 r(n) is called the seed of the random number generator. 86 87 For all the six generator routines described next, the first 88 computational step is to perform a single iteration of the algorithm. 89 90 <<drand48>> and <<erand48>> 91 return values of type double. The full 48 bits of r(n+1) are 92 loaded into the mantissa of the returned value, with the exponent set 93 such that the values produced lie in the interval [0.0, 1.0]. 94 95 <<lrand48>> and <<nrand48>> 96 return values of type long in the range 97 [0, 2**31-1]. The high-order (31) bits of 98 r(n+1) are loaded into the lower bits of the returned value, with 99 the topmost (sign) bit set to zero. 100 101 <<mrand48>> and <<jrand48>> 102 return values of type long in the range 103 [-2**31, 2**31-1]. The high-order (32) bits of 104 r(n+1) are loaded into the returned value. 105 106 <<drand48>>, <<lrand48>>, and <<mrand48>> 107 use an internal buffer to store r(n). For these functions 108 the initial value of r(0) = 0x1234abcd330e = 20017429951246. 109 110 On the other hand, <<erand48>>, <<nrand48>>, and <<jrand48>> 111 use a user-supplied buffer to store the seed r(n), 112 which consists of an array of 3 shorts, where the zeroth member 113 holds the least significant bits. 114 115 All functions share the same multiplicand and addend. 116 117 <<srand48>> is used to initialize the internal buffer r(n) of 118 <<drand48>>, <<lrand48>>, and <<mrand48>> 119 such that the 32 bits of the seed value are copied into the upper 32 bits 120 of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e. 121 Additionally, the constant multiplicand and addend of the algorithm are 122 reset to the default values given above. 123 124 <<seed48>> also initializes the internal buffer r(n) of 125 <<drand48>>, <<lrand48>>, and <<mrand48>>, 126 but here all 48 bits of the seed can be specified in an array of 3 shorts, 127 where the zeroth member specifies the lowest bits. Again, 128 the constant multiplicand and addend of the algorithm are 129 reset to the default values given above. 130 <<seed48>> returns a pointer to an array of 3 shorts which contains 131 the old seed. 132 This array is statically allocated, thus its contents are lost after 133 each new call to <<seed48>>. 134 135 Finally, <<lcong48>> allows full control over the multiplicand and 136 addend used in <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>, 137 <<mrand48>>, and <<jrand48>>, 138 and the seed used in <<drand48>>, <<lrand48>>, and <<mrand48>>. 139 An array of 7 shorts is passed as parameter; the first three shorts are 140 used to initialize the seed; the second three are used to initialize the 141 multiplicand; and the last short is used to initialize the addend. 142 It is thus not possible to use values greater than 0xffff as the addend. 143 144 Note that all three methods of seeding the random number generator 145 always also set the multiplicand and addend for any of the six 146 generator calls. 147 148 For a more powerful random number generator, see <<random>>. 149 150 PORTABILITY 151 SUS requires these functions. 152 153 No supporting OS subroutines are required. 154 */ 155 156 #include "rand48.h" 157 158 void 159 _DEFUN (__dorand48, (r, xseed), 160 struct _reent *r _AND 161 unsigned short xseed[3]) 162 { 163 unsigned long accu; 164 unsigned short temp[2]; 165 166 _REENT_CHECK_RAND48(r); 167 accu = (unsigned long) __rand48_mult[0] * (unsigned long) xseed[0] + 168 (unsigned long) __rand48_add; 169 temp[0] = (unsigned short) accu; /* lower 16 bits */ 170 accu >>= sizeof(unsigned short) * 8; 171 accu += (unsigned long) __rand48_mult[0] * (unsigned long) xseed[1] + 172 (unsigned long) __rand48_mult[1] * (unsigned long) xseed[0]; 173 temp[1] = (unsigned short) accu; /* middle 16 bits */ 174 accu >>= sizeof(unsigned short) * 8; 175 accu += __rand48_mult[0] * xseed[2] + __rand48_mult[1] * xseed[1] + __rand48_mult[2] * xseed[0]; 176 xseed[0] = temp[0]; 177 xseed[1] = temp[1]; 178 xseed[2] = (unsigned short) accu; 179 } 180