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//=================================================================

//

//        rand3.c

//

//        Testcase for C library rand()

//

//=================================================================

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//=================================================================

//#####DESCRIPTIONBEGIN####

//

// Author(s):     jlarmour

// Contributors:  

// Date:          2000-04-30

// Description:   Contains testcode for C library rand() function. This tests

//                that random numbers are distributed well between 0 and

//                RAND_MAX

//

//

//####DESCRIPTIONEND####

// INCLUDES

#include <stdlib.h>

#include <cyg/infra/testcase.h>

// CONSTANTS

#define NUM_BUCKETS 1000     // how many categories to define

#define TEST_LENGTH 200000   // how many samples to take - careful

                             // when reducing this since it also reduces

                             // BUCKET_DIFF_TOLERANCE below. If you reduce

                             // it too low, BUCKET_DIFF_TOLERANCE will need

                             // a fudge factor

#define BUCKET_SIZE    (RAND_MAX / NUM_BUCKETS)  // number space allocated

                                                 // to bucket from 0..RAND_MAX

#define NUM_PER_BUCKET (TEST_LENGTH/NUM_BUCKETS) // Expected number that went

                                                 // into each bucket at end

// how much the buckets can vary at the end.

#define BUCKET_DIFF_TOLERANCE (NUM_PER_BUCKET/4) // allowed to vary 25%

// FUNCTIONS

static __inline__ int

my_abs(int i)

{

    return (i < 0) ? -i : i;

} // my_abs()

int

main(int argc, char *argv[])

{

    // divide the space from 0..RAND_MAX into NUM_BUCKETS categories *BUT*

    // RAND_MAX / NUM_BUCKETS may not divide exactly so we leave space for

    // the bits left over, in case there are any! So we add 1.

    static cyg_uint8 rand_bucket[NUM_BUCKETS+1];

    cyg_ucount32 count;                        // loop variable

    int r;                                     // temp for rand() variable

    CYG_TEST_INIT();

    CYG_TEST_INFO("Starting tests from testcase " __FILE__ " for C library "

                  "rand() function");

    CYG_TEST_INFO("This test tests the distribution of random numbers and");

    CYG_TEST_INFO("may take some time");

    for ( count=0; count < TEST_LENGTH; ++count ) {

        r = rand();

        ++rand_bucket[ r / BUCKET_SIZE ];

        if ((count%10000)==0)

            CYG_TEST_STILL_ALIVE(count, "Still testing...");

    } // for

    for ( count=0; count < NUM_BUCKETS; ++count ) {

        cyg_ucount32 diff;

        diff = my_abs( rand_bucket[count] - NUM_PER_BUCKET );

        if ( diff > BUCKET_DIFF_TOLERANCE )

            break;

    } // for

    // if the previous loop completed, we may want to check the "extra"

    // bucket (see the comment at the top) that may have some bits in if

    // RAND_MAX doesn't split into NUM_BUCKETS evenly. The number of random

    // digits that fell into that bucket would be expected to be proportional

    // to the ratio of the remainder of (RAND_MAX % NUM_BUCKETS) to

    // NUM_BUCKETS. 

    if (count == NUM_BUCKETS) {

        cyg_ucount32 rem;

        cyg_ucount32 last_bucket_expected;

        cyg_ucount32 diff;

        rem = RAND_MAX % NUM_BUCKETS;

        last_bucket_expected = (rem * NUM_PER_BUCKET) / BUCKET_SIZE;

        diff = my_abs(last_bucket_expected - rand_bucket[count]);

        CYG_TEST_PASS_FAIL(diff <= BUCKET_DIFF_TOLERANCE,

                           "Upper bound fencepost test");

    }

    CYG_TEST_PASS_FAIL( (count >= NUM_BUCKETS),

                        "even distribution of rand()");

    CYG_TEST_FINISH("Finished tests from testcase " __FILE__ " for "

                    "C library rand() function");

} // main()

// EOF rand3.c