Tom Lane writes:
> Oh, that's interesting. What platform do you use? If RAND_MAX applies
> to random() on some machines that'd probably explain why the code is
> written like it is. But on my box (HPUX) the rand() function is old
> and crufty and considerably different from random().
rand() and RAND_MAX are defined by ANSI C, random() is a BSD-ism. I
suggest you use the former. Also, while you're at it, this is a snippet
from the C FAQ:
13.16: How can I get random integers in a certain range?
A: The obvious way, rand() % N /* POOR */ (which tries to return numbers from 0
toN-1) is poor, because the low-order bits of many random number generators are distressingly *non*-random.
(See question 13.18.) A better method is something like (int)((double)rand() / ((double)RAND_MAX +
1)* N) If you're worried about using floating point, you could use rand() / (RAND_MAX / N + 1)
Both methods obviously require knowing RAND_MAX (which ANSI #defines in <stdlib.h>), and assume that N is much
lessthan RAND_MAX. (Note, by the way, that RAND_MAX is a *constant* telling you what the fixed range
ofthe C library rand() function is. You cannot set RAND_MAX to some other value, and there is no way of
requestingthat rand() return numbers in some other range.) If you're starting with a random number generator
whichreturns floating-point values between 0 and 1, all you have to do to get integers from 0 to N-1 is
multiplythe output of that generator by N. References: K&R2 Sec. 7.8.7 p. 168; PCS Sec. 11 p. 172.
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Peter Eisentraut Sernanders väg 10:115
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