Use the OvflOffset() macro to try to remove some magic numbers from btree.c.

FossilOrigin-Name: 1541607d458069f5db890b4ebe1c7e14ddf4e360

manifest

@@ -1,5 +1,5 @@
-C Reduce\sthe\ssize\sof\sthe\sCellInfo\sobject\sfrom\s32\sto\s24\sbytes\son\s64-bit\smachines,\nfor\sa\ssmall\sperformance\sincrease\sand\slibrary\ssize\sreduction.
-D 2015-12-30T18:18:46.481
+C Use\sthe\sOvflOffset()\smacro\sto\stry\sto\sremove\ssome\smagic\snumbers\sfrom\sbtree.c.
+D 2015-12-30T20:50:11.553
 F Makefile.in 28bcd6149e050dff35d4dcfd97e890cd387a499d
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 5fff077fcc46de7714ed6eebb6159a4c00eab751
@@ -276,9 +276,9 @@ F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
 F src/backup.c 2869a76c03eb393ee795416e2387005553df72bc
 F src/bitvec.c 1a78d450a17c5016710eec900bedfc5729bf9bdf
 F src/btmutex.c 45a968cc85afed9b5e6cf55bf1f42f8d18107f79
-F src/btree.c 5ac3f868d4f20a67f0f00a1014940f902b511558
+F src/btree.c ec6627fbb483526e0f6e095c0a438191fe6386b3
 F src/btree.h 2d76dee44704c47eed323356a758662724b674a0
-F src/btreeInt.h b5f2651b41808f038dee9282c5dc0232ce6532d3
+F src/btreeInt.h dc698b04ae266bcce5f2eebba007133bf2339ef5
 F src/build.c 5a8611a01cbf67c736d81304e054ec361ef8963d
 F src/callback.c 7b44ce59674338ad48b0e84e7b72f935ea4f68b0
 F src/complete.c addcd8160b081131005d5bc2d34adf20c1c5c92f
@@ -1406,8 +1406,10 @@ F tool/vdbe_profile.tcl 246d0da094856d72d2c12efec03250d71639d19f
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 3d81dfe3bc5ca9588b7796769d9be7a182f38b1c 7850715406458a61cff9eba5ad915f61f6d99482
-R 53c67154b7bbcd33ca0c18e39c81df1f
-T +closed 7850715406458a61cff9eba5ad915f61f6d99482
+P 6a4cfc7ab62046eb718ce59eff6b632f239312ac
+R c06b170488f3c7c74619bb001be96ae6
+T *branch * ovfloffset-macro
+T *sym-ovfloffset-macro *
+T -sym-trunk *
 U drh
-Z f674907b91bbe0647e025dbc39f72b55
+Z bc33053752556a2a7906fec188dea6ee

manifest.uuid

@@ -1 +1 @@
-6a4cfc7ab62046eb718ce59eff6b632f239312ac
+1541607d458069f5db890b4ebe1c7e14ddf4e360

src/btree.c

@@ -1306,7 +1306,7 @@ static void ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell, int *pRC){
   assert( pCell!=0 );
   pPage->xParseCell(pPage, pCell, &info);
   if( info.nLocal<info.nPayload ){
-    Pgno ovfl = get4byte(&pCell[info.nSize-4]);
+    Pgno ovfl = get4byte(&pCell[OvflOffset(&info)]);
     ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno, pRC);
   }
 }
@@ -3346,9 +3346,9 @@ static int modifyPagePointer(MemPage *pPage, Pgno iFrom, Pgno iTo, u8 eType){
         pPage->xParseCell(pPage, pCell, &info);
         if( info.nLocal<info.nPayload
          && pCell+info.nSize-1<=pPage->aData+pPage->maskPage
-         && iFrom==get4byte(pCell+info.nSize-4)
+         && iFrom==get4byte(pCell+OvflOffset(&info))
         ){
-          put4byte(pCell+info.nSize-4, iTo);
+          put4byte(pCell+OvflOffset(&info), iTo);
           break;
         }
       }else{
@@ -6855,7 +6855,7 @@ static int ptrmapCheckPages(MemPage **apPage, int nPage){
       z = findCell(pPage, j);
       pPage->xParseCell(pPage, z, &info);
       if( info.nLocal<info.nPayload ){
-        Pgno ovfl = get4byte(&z[info.nSize-4]);
+        Pgno ovfl = get4byte(&z[OvflOffset(&info)]);
         ptrmapGet(pBt, ovfl, &e, &n);
         assert( n==pPage->pgno && e==PTRMAP_OVERFLOW1 );
       }

src/btreeInt.h

@@ -473,6 +473,13 @@ struct CellInfo {
   u16 nSize;     /* Size of the cell content on the main b-tree page */
 };
 
+/* If X is a pointer to a CellInfo object for a cell, then OvflOffset(X) is 
+** the offset from the start of that cell to the first overflow page number 
+** for for that cell.
+*/
+#define OvflOffset(X)  ((X)->nSize-4)
+
+
 /*
 ** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than
 ** this will be declared corrupt. This value is calculated based on a