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Improved sort function in the percentile extension.

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FossilOrigin-Name: 9f84e8d59bcda642e732565e840f6a880a01b2fc65af2651248f6a8a6e1cb65a
This commit is contained in:
drh
2024-09-01 18:54:31 +00:00
parent 41155d8885
commit c97ad9b4e1
3 changed files with 41 additions and 39 deletions
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66
ext/misc/percentile.c
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@ -271,6 +271,11 @@ static void percentStep(sqlite3_context *pCtx, int argc, sqlite3_value **argv){
}
}
/*
** Interchange two doubles.
*/
#define SWAP_DOUBLE(X,Y) {double ttt=(X);(X)=(Y);(Y)=ttt;}
/*
** Sort an array of doubles.
**
@ -283,49 +288,44 @@ static void percentStep(sqlite3_context *pCtx, int argc, sqlite3_value **argv){
** (2) To avoid the function call to the comparison routine for each
** comparison.
*/
static void sortDoubles(double *a, int n){
int iLt; /* Entries with index less than iLt are less than rPivot */
int iGt; /* Entries with index iGt or more are greater than rPivot */
static void percentSort(double *a, unsigned int n){
int iLt; /* Entries before a[iLt] are less than rPivot */
int iGt; /* Entries at or after a[iGt] are greater than rPivot */
int i; /* Loop counter */
double rPivot; /* The pivot value */
double rTmp; /* Temporary used to swap two values */
if( n<2 ) return;
if( n>5 ){
double x[3];
x[0]= a[0];
x[1] = a[n/2];
x[2] = a[n-1];
sortDoubles(x,3);
rPivot = x[1];
}else{
rPivot = a[n/2];
assert( n>=2 );
if( a[0]>a[n-1] ){
SWAP_DOUBLE(a[0],a[n-1])
}
iLt = i = 0;
iGt = n;
while( i<iGt ){
if( n==2 ) return;
iGt = n-1;
i = n/2;
if( a[0]>a[i] ){
SWAP_DOUBLE(a[0],a[i])
}else if( a[i]>a[iGt] ){
SWAP_DOUBLE(a[i],a[iGt])
}
if( n==3 ) return;
rPivot = a[i];
iLt = i = 1;
do{
if( a[i]<rPivot ){
if( i>iLt ){
rTmp = a[i];
a[i] = a[iLt];
a[iLt] = rTmp;
}
if( i>iLt ) SWAP_DOUBLE(a[i],a[iLt])
iLt++;
i++;
}else if( a[i]>rPivot ){
do{
iGt--;
}while( iGt>i && a[iGt]>rPivot );
rTmp = a[i];
a[i] = a[iGt];
a[iGt] = rTmp;
SWAP_DOUBLE(a[i],a[iGt])
}else{
i++;
}
}
if( iLt>=2 ) sortDoubles(a, iLt);
if( n-iGt>=2 ) sortDoubles(a+iGt, n-iGt);
}while( i<iGt );
if( iLt>=2 ) percentSort(a, iLt);
if( n-iGt>=2 ) percentSort(a+iGt, n-iGt);
/* Uncomment for testing */
#if 0
for(i=0; i<n-1; i++){
@ -366,7 +366,8 @@ static void percentInverse(sqlite3_context *pCtx,int argc,sqlite3_value **argv){
return;
}
if( p->bSorted==0 ){
sortDoubles(p->a, p->nUsed);
assert( p->nUsed>1 );
percentSort(p->a, p->nUsed);
p->bSorted = 1;
}else{
percentAssertSorted(p);
@ -398,7 +399,8 @@ static void percentCompute(sqlite3_context *pCtx, int bIsFinal){
if( p->a==0 ) return;
if( p->nUsed ){
if( p->bSorted==0 ){
sortDoubles(p->a, p->nUsed);
assert( p->nUsed>1 );
percentSort(p->a, p->nUsed);
p->bSorted = 1;
}else{
percentAssertSorted(p);