COIN-OR::LEMON - Graph Library

source: lemon-benchmark/generators/netgen/random.c @ 9:7768d68909e8

Last change on this file since 9:7768d68909e8 was 6:a3ef33a8694a, checked in by Alpar Juttner <alpar@…>, 14 years ago

Add netgen generator

File size: 1.0 KB
Line 
1/*** This is a portable random number generator whose origins are
2 *** unknown.  As far as can be told, this is public domain software.
3
4
5/*** portable random number generator */
6
7/*** Note that every variable used here must have at least 31 bits
8 *** of precision, exclusive of sign.  Long integers should be enough.
9 *** The generator is the congruential:  i = 7**5 * i mod (2^31-1).
10 ***/
11
12#define MULTIPLIER 16807
13#define MODULUS    2147483647
14
15static long saved_seed;
16
17
18/*** set_random - initialize constants and seed */
19
20void set_random(seed)
21long seed;
22{
23  saved_seed = seed;
24}
25
26
27/*** ng_random - generate a random integer in the interval [a,b] (b >= a >= 0) */
28
29long ng_random(a, b)
30long a, b;
31{
32  register long hi, lo;
33
34  hi = MULTIPLIER * (saved_seed >> 16);
35  lo = MULTIPLIER * (saved_seed & 0xffff);
36  hi += (lo>>16);
37  lo &= 0xffff;
38  lo += (hi>>15);
39  hi &= 0x7fff;
40  lo -= MODULUS;
41  if ((saved_seed = (hi<<16) + lo) < 0)
42    saved_seed += MODULUS;
43
44  if (b <= a)
45    return b;
46  return a + saved_seed % (b - a + 1);
47}
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