Improved sort function in the percentile extension.

FossilOrigin-Name: 9f84e8d59bcda642e732565e840f6a880a01b2fc65af2651248f6a8a6e1cb65a

ext/misc/percentile.c

@@ -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.
 **
@@ -283,48 +288,43 @@ 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
@@ -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);

manifest

@@ -1,5 +1,5 @@
-C Fix\sto\sthe\squicksort\salgorithm\sin\sthe\spercentile\sextension.
-D 2024-09-01T10:52:20.432
+C Improved\ssort\sfunction\sin\sthe\spercentile\sextension.
+D 2024-09-01T18:54:31.153
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -410,7 +410,7 @@ F ext/misc/nextchar.c 7877914c2a80c2f181dd04c3dbef550dfb54c93495dc03da2403b5dd58
 F ext/misc/noop.c f1a21cc9b7a4e667e5c8458d80ba680b8bd4315a003f256006046879f679c5a0
 F ext/misc/normalize.c bd84355c118e297522aba74de34a4fd286fc775524e0499b14473918d09ea61f
 F ext/misc/pcachetrace.c f4227ce03fb16aa8d6f321b72dd051097419d7a028a9853af048bee7645cb405
-F ext/misc/percentile.c c5ddb86314a0648c510de54a7290b939225b128925d98b02859c47d98f9ec282
+F ext/misc/percentile.c 4560a3a42bab3d867060bb7e80a15fd82f917a58c87739591f0a3d99f18754a8
 F ext/misc/prefixes.c 82645f79229877afab08c8b08ca1e7fa31921280906b90a61c294e4f540cd2a6
 F ext/misc/qpvtab.c fc189e127f68f791af90a487f4460ec91539a716daf45a0c357e963fd47cc06c
 F ext/misc/randomjson.c ef835fc64289e76ac4873b85fe12f9463a036168d7683cf2b773e36e6262c4ed
@@ -2211,8 +2211,8 @@ F vsixtest/vsixtest.tcl 6195aba1f12a5e10efc2b8c0009532167be5e301abe5b31385638080
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 U drh
-Z 1fbd72dda73eb1323c7b4878ebf0259d
+Z 1672856efafeb853be5cf9a4114de044
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-54313f74b24c46f1afa1ff082ef569fa46938527095be358015e7047e17702ac
+9f84e8d59bcda642e732565e840f6a880a01b2fc65af2651248f6a8a6e1cb65a