rand.cpp

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#include <time.h>   // for clock()
 
// expand _TEST_EXPORT macros
#define _RWSTD_TEST_SRC
#include <rw_rand.h>
 
 
enum { TABLE_SIZE = 55 };
 
static _RWSTD_UINT32_T table32 [TABLE_SIZE];
static _RWSTD_SIZE_T   inx32 [2];
 
 
// seeds the 32-bit random number generator
_TEST_EXPORT void
rw_seed32 (_RWSTD_UINT32_T seed)
{
    if (0xffffffffUL == seed)
        seed = unsigned (clock ());
 
    table32 [TABLE_SIZE - 1] = seed;
 
    _RWSTD_UINT32_T k = 1;
 
    for (_RWSTD_SIZE_T i = 0; i != TABLE_SIZE - 1U; ++i) {
 
        const _RWSTD_SIZE_T ii = 21U * i % TABLE_SIZE;
        table32 [ii] =  k;
        k            = seed - k;
        seed         = table32 [ii];
    }
 
    for (_RWSTD_SIZE_T i = 0; i != 4U; ++i) {
        for (_RWSTD_SIZE_T ii = 0; ii != TABLE_SIZE; ++ii)
            table32 [i] = table32 [i] - table32 [(i + 31U) % TABLE_SIZE];
    }
 
    inx32 [0] = 0U;
    inx32 [1] = TABLE_SIZE * 2U / 3U - 1U;
}
 
 
// returns a 32-bit random number in the range [0, limit)
// if limit is non-zero, otherwise in the range [0, UINT32_MAX)
_TEST_EXPORT _RWSTD_UINT32_T
rw_rand32 (_RWSTD_UINT32_T limit /* = 0 */)
{
    if (0 == inx32 [0] && 0 == inx32 [1])
        rw_seed32 (161803398);
 
    table32 [++inx32 [0] %= TABLE_SIZE] -=
        table32 [++inx32 [1] %= TABLE_SIZE];
 
    return limit ? table32 [inx32 [0]] % limit : table32 [inx32 [0]];
}
 
 
#ifdef _RWSTD_UINT64_T
 
static _RWSTD_UINT64_T table64 [TABLE_SIZE];
static _RWSTD_SIZE_T   inx64 [2];
 
 
// seeds the 64-bit random number generator
_TEST_EXPORT void
rw_seed64 (_RWSTD_UINT64_T seed)
{
    if ((_RWSTD_UINT64_T)-1 == seed)
        seed = clock ();
 
    table64 [TABLE_SIZE - 1] = seed;
 
    _RWSTD_UINT64_T k = 1;
 
    for (_RWSTD_SIZE_T i = 0; i != TABLE_SIZE - 1U; ++i) {
 
        const _RWSTD_SIZE_T ii = 21U * i % TABLE_SIZE;
        table64 [ii] =  k;
        k            = seed - k;
        seed         = table64 [ii];
    }
 
    for (_RWSTD_SIZE_T i = 0; i != 4U; ++i) {
        for (_RWSTD_SIZE_T ii = 0; ii != TABLE_SIZE; ++ii)
            table64 [i] = table64 [i] - table64 [(i + 31U) % TABLE_SIZE];
    }
 
    inx64 [0] = 0U;
    inx64 [1] = TABLE_SIZE * 2U / 3U - 1U;
}
 
 
// returns a 64-bit random number in the range [0, limit)
// if limit is non-zero, otherwise in the range [0, UINT64_MAX)
_TEST_EXPORT _RWSTD_UINT64_T
rw_rand64 (_RWSTD_UINT64_T limit)
{
    if (0 == inx64 [0] && 0 == inx64 [1])
        rw_seed64 (161803398);
 
    table64 [++inx64 [0] %= TABLE_SIZE] -=
        table64 [++inx64 [1] %= TABLE_SIZE];
 
    return limit ? table64 [inx64 [0]] % limit : table64 [inx64 [0]];
}
 
#endif   // _RWSTD_UINT64_T