From: drh <>
Date: Sat, 6 Jun 2026 17:20:35 +0000 (+0000)
Subject: Minor performance enhancement and improved comments on the quicksort
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=6bf7825ac5afd870fbe69c0eb82cddbb031de171;p=thirdparty%2Fsqlite.git

Minor performance enhancement and improved comments on the quicksort
algorithm used by the median() implementation in func.c.

FossilOrigin-Name: 2800f6a75bbb6ddc86f2e029a7d36ff08febe03812302fb7931eb68da316f74d
---

diff --git a/manifest b/manifest
index 836a7ba8c7..95c14414c3 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Disable\sthe\svector-IN-SELECT\soptimization\sif\sthe\snumber\sof\scolumns\sis\sso\nlarge\sthat\sit\swould\scause\sthe\sWhereTerm.nChild\scolumn\sto\swrap.\n[bugs:/info/2026-06-04T10:00:49Z|Bug\s2026-06-04T10:00:49Z].
-D 2026-06-04T16:56:11.519
+C Minor\sperformance\senhancement\sand\simproved\scomments\son\sthe\squicksort\nalgorithm\sused\sby\sthe\smedian()\simplementation\sin\sfunc.c.
+D 2026-06-06T17:20:35.028
 F .fossil-settings/binary-glob 61195414528fb3ea9693577e1980230d78a1f8b0a54c78cf1b9b24d0a409ed6a x
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
@@ -691,7 +691,7 @@ F src/delete.c 59eeca3fb88c29329afc41bb803ee568b120d9dd7470b5f38ab55cc38390b451
 F src/expr.c e97dd9f6ada4c448764e225d8963091bf630b3efb2c92e4d0762571cca2a14e5
 F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
 F src/fkey.c 931f74cec1dc8038a0217ef340c91ce147dd1bbed08dc40c47ee0ec6edfffb08
-F src/func.c 2837560c6232b7a3c9c163137a210d820ca82af2c33a5d446599fcb16c09192e
+F src/func.c 2fc6a53626184593eacb78a2bbf22b779da126f5ee17fb31c93245a95b89fa3d
 F src/global.c a19e4b1ca1335f560e9560e590fc13081e21f670643367f99cb9e8f9dc7d615b
 F src/hash.c 03c8c0f4be9e8bcb6de65aa26d34a61d48a9430747084a69f9469fbb00ea52ca
 F src/hash.h 46b92795a95bfefb210f52f0c316e9d7cdbcdd7e7fcfb0d8be796d3a5767cddf
@@ -2208,8 +2208,8 @@ F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee
 F tool/warnings.sh a554d13f6e5cf3760f041b87939e3d616ec6961859c3245e8ef701d1eafc2ca2
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
 F tool/winmain.c 00c8fb88e365c9017db14c73d3c78af62194d9644feaf60e220ab0f411f3604c
-P b4b9dc632b06f932759bc2fceeb6fa1dd6e0de329106ae1d34be874ea1695859
-R 67f36e9dbaba8a59d341f8d5b8046ceb
+P bb49dfc948048779a30deff9a3d1bb39846f6f72c26a2bdcdd0e386251720fe6
+R 25eea2f89977a68603b411d8091b0f1b
 U drh
-Z 5b04f3e9d03d2969d7a4a1df2153634f
+Z ec2984844ba1e4eca06b386926ff2a98
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index b896730f1b..d25bbcae54 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-bb49dfc948048779a30deff9a3d1bb39846f6f72c26a2bdcdd0e386251720fe6
+2800f6a75bbb6ddc86f2e029a7d36ff08febe03812302fb7931eb68da316f74d
diff --git a/src/func.c b/src/func.c
index dd33af13a4..f14b64173b 100644
--- a/src/func.c
+++ b/src/func.c
@@ -2974,7 +2974,8 @@ static void percentSort(double *a, unsigned int n){
   int i;         /* Loop counter */
   double rPivot; /* The pivot value */
 
-  while( n>=2 ){
+  assert( n>=2 );
+  do{
     if( a[0]>a[n-1] ){
       SWAP_DOUBLE(a[0],a[n-1])
     }
@@ -3003,6 +3004,11 @@ static void percentSort(double *a, unsigned int n){
         i++;
       }
     }while( i<iGt );
+
+    /* Recurse on the smaller partition only.  The smaller partition
+    ** will hold n/2 or fewer entries, which assures that the stack
+    ** depth will not exceed O(log(n)), even for pathological cases.
+    ** Loop without recursion for the larger partition. */
     if( iLt>n/2 ){
       if( n-iGt>=2 ) percentSort(a+iGt, n-iGt);
       n = iLt;
@@ -3011,7 +3017,7 @@ static void percentSort(double *a, unsigned int n){
       a += iGt;
       n -= iGt;
     }
-  }
+  }while( n>=2 );
 }
 
 /*