Size and performance optimization in btreeInitPage() in the freeblock

validation step.

FossilOrigin-Name: 57deb1b412e0c328528f2b4d697e326bfd028dca

manifest

@@ -1,5 +1,5 @@
-C Change\sthe\sorder\sof\scomparison\sfor\sdivider\scell\soverflow\sin\sbalance\snon-root\nto\savoid\sa\s(harmless)\sreference\sto\san\suninitialized\svariable.
+C Size\sand\sperformance\soptimization\sin\sbtreeInitPage()\sin\sthe\sfreeblock\nvalidation\sstep.
-D 2016-12-12T00:58:40.524
+D 2016-12-12T01:30:01.538
 F Makefile.in 7639c6a09da11a9c7c6f2630fc981ee588d1072d
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc b8ca53350ae545e3562403d5da2a69cec79308da
@@ -331,7 +331,7 @@ F src/auth.c 930b376a9c56998557367e6f7f8aaeac82a2a792
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c bc87dd3b062cc26edfe79918de2200ccb8d41e73
-F src/btree.c 5299b39ca2ae3a177aa4f10c32adecb6ae3dfb2e
+F src/btree.c 383ce69bd36b0f409bfb8bd028786b2f0a4cbb24
 F src/btree.h 2349a588abcd7e0c04f984e15c5c777b61637583
 F src/btreeInt.h 10c4b77c2fb399580babbcc7cf652ac10dba796e
 F src/build.c 178f16698cbcb43402c343a9413fe22c99ffee21
@@ -1536,7 +1536,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 35ecd4ebc55579175f7c934e4eb1edb969008428
+P f9f2e23bbd68a8994621623446868d666df52eff
-R 4eec70a8d01ab30e743f435be503a7d5
+R d6e7ff9713db8a1c5bca23b53d1ed305
 U drh
-Z 5a1985fcb882d74ad54a7fce35ec702f
+Z a7e99aa30e3b05522d980cd982791774

manifest.uuid

@@ -1 +1 @@
-f9f2e23bbd68a8994621623446868d666df52eff
+57deb1b412e0c328528f2b4d697e326bfd028dca

src/btree.c

@@ -1743,7 +1743,7 @@ static int btreeInitPage(MemPage *pPage){
   assert( pPage->aData == sqlite3PagerGetData(pPage->pDbPage) );
 
   if( !pPage->isInit ){
-    u16 pc;            /* Address of a freeblock within pPage->aData[] */
+    u32 pc;            /* Address of a freeblock within pPage->aData[] */
     u8 hdr;            /* Offset to beginning of page header */
     u8 *data;          /* Equal to pPage->aData */
     BtShared *pBt;        /* The main btree structure */
@@ -1823,26 +1823,31 @@ static int btreeInitPage(MemPage *pPage){
     ** freeblocks. */
     pc = get2byte(&data[hdr+1]);
     nFree = data[hdr+7] + top;  /* Init nFree to non-freeblock free space */
-    while( pc>0 ){
+    if( pc>0 ){
-      u16 next, size;
+      u32 next, size;
-      if( pc<iCellFirst || pc>iCellLast ){
+      if( pc<iCellFirst ){
         /* EVIDENCE-OF: R-55530-52930 In a well-formed b-tree page, there will
         ** always be at least one cell before the first freeblock.
-        **
-        ** Or, the freeblock is off the end of the page
         */
         return SQLITE_CORRUPT_BKPT; 
       }
+      while( 1 ){
+        if( pc>iCellLast ){
+          return SQLITE_CORRUPT_BKPT; /* Freeblock off the end of the page */
+        }
         next = get2byte(&data[pc]);
         size = get2byte(&data[pc+2]);
-      if( (next>0 && next<=pc+size+3) || pc+size>usableSize ){
-        /* Free blocks must be in ascending order. And the last byte of
-        ** the free-block must lie on the database page.  */
-        return SQLITE_CORRUPT_BKPT; 
-      }
         nFree = nFree + size;
+        if( next<=pc+size+3 ) break;
         pc = next;
       }
+      if( next>0 ){
+        return SQLITE_CORRUPT_BKPT;  /* Freeblock not in ascending order */
+      }
+      if( pc+size>usableSize ){
+        return SQLITE_CORRUPT_BKPT;  /* Last freeblock extends past page end */
+      }
+    }
 
     /* At this point, nFree contains the sum of the offset to the start
     ** of the cell-content area plus the number of free bytes within