Add comments to sqlite3ExprCompare() to clarify its operation. Ticket #2216. (CVS 3663)

FossilOrigin-Name: fba0a1e50820677081bc7cf01f97bf953065f7c4

manifest

@@ -1,5 +1,5 @@
-C Additional\stest\scases\sadded.\s\sImprovements\sto\sthe\sINSERT\stransfer\noptimization.\s(CVS\s3662)
-D 2007-02-24T15:18:50
+C Add\scomments\sto\ssqlite3ExprCompare()\sto\sclarify\sits\soperation.\sTicket\s#2216.\s(CVS\s3663)
+D 2007-02-24T15:29:04
 F Makefile.in 1fe3d0b46e40fd684e1e61f8e8056cefed16de9f
 F Makefile.linux-gcc 2d8574d1ba75f129aba2019f0b959db380a90935
 F README 9c4e2d6706bdcc3efdd773ce752a8cdab4f90028
@@ -65,7 +65,7 @@ F src/complete.c 7d1a44be8f37de125fcafd3d3a018690b3799675
 F src/date.c 393c73fc027597e008dcd81454544659e978b05c
 F src/delete.c 151d08386bf9c9e7f92f6b9106c71efec2def184
 F src/experimental.c 1b2d1a6cd62ecc39610e97670332ca073c50792b
-F src/expr.c 3fc187bc438f5637332b2a01b1bf6f728cf2830c
+F src/expr.c 824f026e74d1287212bad75c8a2858c349229e03
 F src/func.c b7e1e220a6795ecae7649815145ea5f8644dfa5f
 F src/hash.c 449f3d6620193aa557f5d86cbc5cc6b87702b185
 F src/hash.h 1b3f7e2609141fd571f62199fc38687d262e9564
@@ -434,7 +434,7 @@ F www/tclsqlite.tcl bb0d1357328a42b1993d78573e587c6dcbc964b9
 F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
 F www/version3.tcl 890248cf7b70e60c383b0e84d77d5132b3ead42b
 F www/whentouse.tcl 97e2b5cd296f7d8057e11f44427dea8a4c2db513
-P 830985814345f71ba2def3c206e36aabe9e1ee7c
-R 05e26f17eb8b96bb85b027f957e8b674
+P 2bf5475bde763f73f7f4dd9cac7d13a631a7d2aa
+R bf7e89dd91722385f525c6269433be59
 U drh
-Z 43981f64256c87de6c82c0452ce773e2
+Z 359d2bb09f0008f8bf6cf7c87fededb5

manifest.uuid

@@ -1 +1 @@
-2bf5475bde763f73f7f4dd9cac7d13a631a7d2aa
+fba0a1e50820677081bc7cf01f97bf953065f7c4

src/expr.c

@@ -12,7 +12,7 @@
 ** This file contains routines used for analyzing expressions and
 ** for generating VDBE code that evaluates expressions in SQLite.
 **
-** $Id: expr.c,v 1.279 2007/02/24 13:53:05 drh Exp $
+** $Id: expr.c,v 1.280 2007/02/24 15:29:04 drh Exp $
 */
 #include "sqliteInt.h"
 #include <ctype.h>
@@ -2187,6 +2187,16 @@ void sqlite3ExprIfFalse(Parse *pParse, Expr *pExpr, int dest, int jumpIfNull){
 /*
 ** Do a deep comparison of two expression trees.  Return TRUE (non-zero)
 ** if they are identical and return FALSE if they differ in any way.
+**
+** Sometimes this routine will return FALSE even if the two expressions
+** really are equivalent.  If we cannot prove that the expressions are
+** identical, we return FALSE just to be safe.  So if this routine
+** returns false, then you do not really know for certain if the two
+** expressions are the same.  But if you get a TRUE return, then you
+** can be sure the expressions are the same.  In the places where
+** this routine is used, it does not hurt to get an extra FALSE - that
+** just might result in some slightly slower code.  But returning
+** an incorrect TRUE could lead to a malfunction.
 */
 int sqlite3ExprCompare(Expr *pA, Expr *pB){
   int i;