Tweaks to the SUBSTR() function to make it dramatically faster in the common

case where the input string is large but the 2nd and 3rd arguments are small
positive integers.

FossilOrigin-Name: 5a474a867c5988ad5ec03719516fdd38f0da5c2c

diff --git a/manifest b/manifest
index 9c937841a07a3aa3b527fb0a7cacb8615a27a33c..f7b1f32f51c5d8702f3d4b3f2fa3901727aca421 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Allow\smedia\ssector\ssizes\sas\ssmall\sas\s32.\s\sThe\sformer\sminimum\ssize\swas\s512.
-D 2009-11-11T13:17:08
+C Tweaks\sto\sthe\sSUBSTR()\sfunction\sto\smake\sit\sdramatically\sfaster\sin\sthe\scommon\ncase\swhere\sthe\sinput\sstring\sis\slarge\sbut\sthe\s2nd\sand\s3rd\sarguments\sare\ssmall\npositive\sintegers.
+D 2009-11-11T20:53:31
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in 53f3dfa49f28ab5b80cb083fb7c9051e596bcfa1
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -120,7 +120,7 @@ F src/delete.c ec04635d152debdab70d4b30c5516b59282075ea
 F src/expr.c be605c60ff84699f3087209f2f86a140a6a5e96c
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 41219cba186bcf0a053e42327dfa23aaba4f834a
-F src/func.c 5949e2633bb8ff57cc70c1904db171ba23f13537
+F src/func.c 97cb15ef7a7c32293a938589c9eb6933f6688a21
 F src/global.c 271952d199a8cc59d4ce840b3bbbfd2f30c8ba32
 F src/hash.c 458488dcc159c301b8e7686280ab209f1fb915af
 F src/hash.h 2894c932d84d9f892d4b4023a75e501f83050970
@@ -770,14 +770,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 09b4f19f100fe82a8321b9ded99e679b7eedc1fa
-R 4660953738e09e48658e726d4ab4929b
+P 5a32bfc17ed022c85d2615c34b41a3dcae2594bd
+R 40ba71f59fe4e9d89ef2ec58e5f61b4f
 U drh
-Z eb38c72c7392595b8c9af9da37273b2d
+Z 900447894e5e2bfd8a391e7b7ee91c4f
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFK+rlYoxKgR168RlERAkd5AJ0ZWUnPqChJybXaCT0e1e2vLdOf+ACePwEx
-ifVUs5BZPo6twb6xD420UW4=
-=eW+2
+iD8DBQFK+yROoxKgR168RlERAgxxAKCHj71qH3RTTKkacqnNolY2rfQh3ACfYfTz
+I5+1whsNXmr3GYydKvNnoeA=
+=f867
 -----END PGP SIGNATURE-----

diff --git a/manifest.uuid b/manifest.uuid
index 00cbd8348986da6b18b94c8adcafe00ab537d01c..b8542ab8145abd98596a10f31b05043858ba65ab 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-5a32bfc17ed022c85d2615c34b41a3dcae2594bd
\ No newline at end of file
+5a474a867c5988ad5ec03719516fdd38f0da5c2c
\ No newline at end of file

diff --git a/src/func.c b/src/func.c
index 980d04edb6fd0c0d942a4b26f4eb66e39c85717f..e1ad9a36cc0598e8fb425f8ab7d1602dfcb4fbd0 100644 (file)
--- a/src/func.c
+++ b/src/func.c
@@ -177,6 +177,7 @@ static void substrFunc(
     return;
   }
   p0type = sqlite3_value_type(argv[0]);
+  p1 = sqlite3_value_int(argv[1]);
   if( p0type==SQLITE_BLOB ){
     len = sqlite3_value_bytes(argv[0]);
     z = sqlite3_value_blob(argv[0]);
@@ -186,11 +187,12 @@ static void substrFunc(
     z = sqlite3_value_text(argv[0]);
     if( z==0 ) return;
     len = 0;
-    for(z2=z; *z2; len++){
-      SQLITE_SKIP_UTF8(z2);
+    if( p1<0 ){
+      for(z2=z; *z2; len++){
+        SQLITE_SKIP_UTF8(z2);
+      }
     }
   }
-  p1 = sqlite3_value_int(argv[1]);
   if( argc==3 ){
     p2 = sqlite3_value_int(argv[2]);
     if( p2<0 ){
@@ -220,10 +222,6 @@ static void substrFunc(
     }
   }
   assert( p1>=0 && p2>=0 );
-  if( p1+p2>len ){
-    p2 = len-p1;
-    if( p2<0 ) p2 = 0;
-  }
   if( p0type!=SQLITE_BLOB ){
     while( *z && p1 ){
       SQLITE_SKIP_UTF8(z);
@@ -234,6 +232,10 @@ static void substrFunc(
     }
     sqlite3_result_text(context, (char*)z, (int)(z2-z), SQLITE_TRANSIENT);
   }else{
+    if( p1+p2>len ){
+      p2 = len-p1;
+      if( p2<0 ) p2 = 0;
+    }
     sqlite3_result_blob(context, (char*)&z[p1], (int)p2, SQLITE_TRANSIENT);
   }
 }