prenex/myqsort
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optimization that does not work, but is maybe not totally bad

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This commit is contained in:
Richard Thier 2025-04-08 01:33:11 +02:00
parent bc500c84e8
commit cebc516125
1 changed files with 12 additions and 25 deletions
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37
qsort.h
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@ -102,15 +102,14 @@ static inline pret3 partition3(uint32_t array[], int low, int high, uint32_t piv
/* index until smaller or eq elements lay */ /* index until smaller or eq elements lay */
int i = (low - 1); int i = (low - 1);
uint32_t pc = 0; /* index until smaller or eq elements lay */
int i2 = (high + 1);
/* traverse each element of the array */ /* traverse each element of the array */
/* compare them with the pivot */ /* compare them with the pivot */
int j2 = high; // j2 > i; --j2) {
#pragma GCC unroll 4 #pragma GCC unroll 4
for (int j = low; j <= high; ++j) { for (int j = low; j <= high; ++j) {
/* Branchless pivot-count */
pc += (array[j] == pivot);
if(array[j] < pivot) { if(array[j] < pivot) {
/* if element smaller than pivot is found */ /* if element smaller than pivot is found */
/* swap it with the greater element pointed by i */ /* swap it with the greater element pointed by i */
@ -119,28 +118,16 @@ static inline pret3 partition3(uint32_t array[], int low, int high, uint32_t piv
/* swap element at i with element at j */ /* swap element at i with element at j */
swapit(&array[i], &array[j]); swapit(&array[i], &array[j]);
} }
} if(j2 > i) {
if (array[j2] > pivot) {
/* if element smaller than pivot is found */
/* swap it with the greater element pointed by i */
--i2;
/* Can spare out the second loop in these cases */ /* swap element at i with element at j */
if(pc < 2) { swapit(&array[i2], &array[j2]);
pret3 ret; }
ret.leftend = i; --j2;
ret.rightend = i + 1;
return ret;
}
/* index until smaller or eq elements lay */
int i2 = (high + 1);
#pragma GCC unroll 4
for (int j = high; j > i; --j) {
if (array[j] > pivot) {
/* if element smaller than pivot is found */
/* swap it with the greater element pointed by i */
--i2;
/* swap element at i with element at j */
swapit(&array[i2], &array[j]);
} }
} }