diff options
Diffstat (limited to 'lib/libc')
| -rw-r--r-- | lib/libc/stdlib/rand.3 | 26 | ||||
| -rw-r--r-- | lib/libc/stdlib/rand.c | 53 |
2 files changed, 74 insertions, 5 deletions
diff --git a/lib/libc/stdlib/rand.3 b/lib/libc/stdlib/rand.3 index f2e37421b6ac..2aadd6cce6b7 100644 --- a/lib/libc/stdlib/rand.3 +++ b/lib/libc/stdlib/rand.3 @@ -35,12 +35,13 @@ .\" .\" @(#)rand.3 8.1 (Berkeley) 6/4/93 .\" -.Dd June 4, 1993 +.Dd May 25, 1999 .Dt RAND 3 .Os .Sh NAME .Nm rand , -.Nm srand +.Nm srand , +.Nm rand_r .Nd bad random number generator .Sh SYNOPSIS .Fd #include <stdlib.h> @@ -48,6 +49,8 @@ .Fn srand "unsigned seed" .Ft int .Fn rand void +.Ft int +.Fn rand_r "unsigned *ctx" .Sh DESCRIPTION .Bf -symbolic These interfaces are obsoleted by random(3). @@ -63,15 +66,26 @@ of 0 to .Pp The .Fn srand -function sets its argument as the seed for a new sequence of +function sets its argument +.Fa seed +as the seed for a new sequence of pseudo-random numbers to be returned by .Fn rand . These sequences are repeatable by calling .Fn srand with the same seed value. .Pp -If no seed value is provided, the functions are automatically +If no +.Fa seed +value is provided, the functions are automatically seeded with a value of 1. +.Pp +.Fn rand_r +provides the same functionality as +.Fn rand . +A pointer to the context value +.Fa ctx +must be supplied by the caller. .Sh SEE ALSO .Xr random 3 .Sh STANDARDS @@ -82,3 +96,7 @@ and functions conform to .St -ansiC . +.Pp +The +.Fn rand_r +function is as proposed in the POSIX.4a Draft #6 document. diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c index 12846c343037..94f6b501ac67 100644 --- a/lib/libc/stdlib/rand.c +++ b/lib/libc/stdlib/rand.c @@ -29,6 +29,8 @@ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. + * + * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. */ #if defined(LIBC_SCCS) && !defined(lint) @@ -38,12 +40,32 @@ static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; #include <sys/types.h> #include <stdlib.h> +#ifdef TEST +#include <stdio.h> +#endif /* TEST */ + +static int +do_rand(unsigned long *ctx) +{ + return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); +} + + +int +rand_r(unsigned int *ctx) +{ + u_long val = (u_long) *ctx; + *ctx = do_rand(&val); + return (int) *ctx; +} + + static u_long next = 1; int rand() { - return ((next = next * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); + return do_rand(&next); } void @@ -52,3 +74,32 @@ u_int seed; { next = seed; } + +#ifdef TEST + +main() +{ + int i; + unsigned myseed; + + printf("seeding rand with 0x19610910: \n"); + srand(0x19610910); + + printf("generating three pseudo-random numbers:\n"); + for (i = 0; i < 3; i++) + { + printf("next random number = %d\n", rand()); + } + + printf("generating the same sequence with rand_r:\n"); + myseed = 0x19610910; + for (i = 0; i < 3; i++) + { + printf("next random number = %d\n", rand_r(&myseed)); + } + + return 0; +} + +#endif /* TEST */ + |