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Importing good random number generator from testlib for use in quicksort and perhaps later in cuckoo hashing.

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This commit is contained in:
Richard Brooksby 2016-03-19 08:57:27 +00:00
parent ed69abbd66
commit 20a34ca17f
2 changed files with 36 additions and 3 deletions
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36
mps/code/mpm.c
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@ -645,6 +645,38 @@ Bool StringEqual(const char *s1, const char *s2)
}
/* Random -- a random number generator
*
* TODO: This is a copy of the generator from testlib.c, which has
* extensive notes and verification tests. The notes need to go to a
* design document, and the tests to a test.
*/
static unsigned RandomSeed = 1;
#define Random_m 2147483647UL
#define Random_a 48271UL
unsigned Random32(void)
{
AVER(UINT_MAX >= 4294967295U);
/* requires m == 2^31-1, a < 2^16 */
unsigned bot = Random_a * (RandomSeed & 0x7FFF);
unsigned top = Random_a * (RandomSeed >> 15);
RandomSeed = bot + ((top & 0xFFFF) << 15) + (top >> 16);
if (RandomSeed > Random_m)
RandomSeed -= Random_m;
return RandomSeed;
}
Word RandomWord(void)
{
Word word;
Index i;
for (i = 0; i < MPS_WORD_WIDTH; i += 31)
word = (word << 31) | Random32();
return word;
}
/* QuickSort -- non-recursive bounded sort
*
* We can't rely on the standard library's qsort, which might have
@ -669,7 +701,6 @@ static Bool quickSorted(void *array[], Count length,
void QuickSort(void *array[], Count length,
QuickSortCompare compare, void *closure)
{
static Index seed = 0x6A9D03;
struct {
Index left, right;
} stack[MPS_WORD_WIDTH];
@ -683,8 +714,7 @@ void QuickSort(void *array[], Count length,
for (;;) {
while (right - left > 1) { /* no need to sort */
/* Pick a random pivot. */
pivot = array[left + seed % (right - left)];
seed = seed * 69069 + 1;
pivot = array[left + RandomWord() % (right - left)];
/* Hoare partition: scan from lo to hi, dividing it into elements
less than the pivot and elements greater or equal. */

3
mps/code/mpm.h
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@ -171,6 +171,9 @@ extern Res WriteF_firstformat_v(mps_lib_FILE *stream, Count depth,
extern size_t StringLength(const char *s);
extern Bool StringEqual(const char *s1, const char *s2);
extern unsigned Random32(void);
extern Word RandomWord(void);
typedef Compare QuickSortCompare(void *left, void *right,
void *closure);
extern void QuickSort(void *array[], Count length,