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- NAME
- rand, srand - random number generator.
- SYNOPSIS
- #include <stdlib.h>
int rand(void);
vector int vrand(void);
void srand(unsigned int seed);
void svrand(vector unsigned seed);
- DESCRIPTION
- The rand() function returns a pseudo-random integer
between 0 and RAND_MAX. The vrand() function returns a
vector integer.
The srand() function sets its argument as the seed for a
new sequence of pseudo-random integers to be returned by
rand(). These sequences are repeatable by calling srand()
with the same seed value. svrand() works in a similar way
but initialises high and low bank differently.
If no seed value is provided, the rand() function is auto
matically seeded with a value of 1 (low bank) and 2 (high
bank.
- RETURN VALUE
- The rand() function returns a value between 0 and
RAND_MAX. The srand() returns no value.
- NOTES
- In Numerical Recipes in C: The Art of Scientific Computing
(William H. Press, Brian P. Flannery, Saul A. Teukolsky,
William T. Vetterling; New York: Cambridge University
Press, 1992 (2nd ed., p. 277)), the following comments are
made:
"If you want to generate a random integer between 1
and 10, you should always do it by using high-order
bits, as in
j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
and never by anything resembling
j=1+(rand() % 10);
(which uses lower-order bits)."
Random-number generation is a complex topic. The Numeri
cal Recipes in C book (see reference above) provides an
excellent discussion of practical random-number generation
issues in Chapter 7 (Random Numbers).
For a more theoretical discussion which also covers many
practical issues in depth, please see Chapter 3 (Random
Numbers) in Donald E. Knuth's The Art of Computer Program
ming, volume 2 (Seminumerical Algorithms), 2nd ed.; Read
ing, Massachusetts: Addison-Wesley Publishing Company,
1981.
- IMPLEMENTATION for apeNEXT:
- These function should NOT be considered to be a good RNG.
Definition at line 98 of file rand.h.
References rand_r(). |
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