Index: src/pager.c
==================================================================
--- src/pager.c
+++ src/pager.c
@@ -16,11 +16,11 @@
 ** is separate from the database file.  The pager also implements file
 ** locking to prevent two processes from writing the same database
 ** file simultaneously, or one process from reading the database while
 ** another is writing.
 **
-** @(#) $Id: pager.c,v 1.188 2005/02/06 02:45:42 drh Exp $
+** @(#) $Id: pager.c,v 1.189 2005/02/15 02:54:15 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 #include "os.h"
 #include "pager.h"
 #include <assert.h>
@@ -166,10 +166,13 @@
   u8 dirty;                      /* TRUE if we need to write back changes */
   u8 needSync;                   /* Sync journal before writing this page */
   u8 alwaysRollback;             /* Disable dont_rollback() for this page */
   short int nRef;                /* Number of users of this page */
   PgHdr *pDirty;                 /* Dirty pages sorted by PgHdr.pgno */
+#ifdef SQLITE_CHECK_PAGES
+  u32 pageHash;
+#endif
   /* pPager->psAligned bytes of page data follow this header */
   /* Pager.nExtra bytes of local data follow the page data */
 };
 
 /*
@@ -448,10 +451,40 @@
   if( pPager->errMask & PAGER_ERR_FULL )    rc = SQLITE_FULL;
   if( pPager->errMask & PAGER_ERR_MEM )     rc = SQLITE_NOMEM;
   if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
   return rc;
 }
+
+#ifdef SQLITE_CHECK_PAGES
+/*
+** Return a 32-bit hash of the page data for pPage.
+*/
+static u32 pager_pagehash(PgHdr *pPage){
+  u32 hash = 0;
+  int i;
+  unsigned char *pData = (unsigned char *)PGHDR_TO_DATA(pPage);
+  for(i=0; i<pPage->pPager->pageSize; i++){
+    hash = (hash+i)^pData[i];
+  }
+  return hash;
+}
+
+/*
+** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
+** is defined, and NDEBUG is not defined, an assert() statement checks
+** that the page is either dirty or still matches the calculated page-hash.
+*/
+#define CHECK_PAGE(x) checkPage(x)
+static void checkPage(PgHdr *pPg){
+  Pager *pPager = pPg->pPager;
+  assert( !pPg->pageHash || pPager->errMask || MEMDB || pPg->dirty || 
+      pPg->pageHash==pager_pagehash(pPg) );
+}
+
+#else
+#define CHECK_PAGE(x)
+#endif
 
 /*
 ** When this is called the journal file for pager pPager must be open.
 ** The master journal file name is read from the end of the file and 
 ** written into memory obtained from sqliteMalloc(). *pzMaster is
@@ -839,10 +872,13 @@
     pPager->aInJournal = 0;
     for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
       pPg->inJournal = 0;
       pPg->dirty = 0;
       pPg->needSync = 0;
+#ifdef SQLITE_CHECK_PAGES
+      pPg->pageHash = pager_pagehash(pPg);
+#endif
     }
     pPager->dirtyCache = 0;
     pPager->nRec = 0;
   }else{
     assert( pPager->dirtyCache==0 || pPager->useJournal==0 );
@@ -956,10 +992,13 @@
       pPager->xDestructor(pData, pPager->pageSize);
     }
     if( pPager->state>=PAGER_EXCLUSIVE ){
       pPg->dirty = 0;
       pPg->needSync = 0;
+#ifdef SQLITE_CHECK_PAGES
+      pPg->pageHash = pager_pagehash(pPg);
+#endif
     }
     CODEC(pPager, pData, pPg->pgno, 3);
   }
   return rc;
 }
@@ -1084,10 +1123,13 @@
         memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
       }
     }
     pPg->needSync = 0;
     pPg->dirty = 0;
+#ifdef SQLITE_CHECK_PAGES
+    pPg->pageHash = pager_pagehash(pPg);
+#endif
   }
   return rc;
 }
 
 /*
@@ -2099,10 +2141,13 @@
       TRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
     }
 #endif
     if( rc ) return rc;
     pList->dirty = 0;
+#ifdef SQLITE_CHECK_PAGES
+    pList->pageHash = pager_pagehash(pList);
+#endif
     pList = pList->pDirty;
   }
   return SQLITE_OK;
 }
 
@@ -2386,10 +2431,13 @@
         }
       }else{
         pPager->nRead++;
       }
     }
+#ifdef SQLITE_CHECK_PAGES
+    pPg->pageHash = pager_pagehash(pPg);
+#endif
   }else{
     /* The requested page is in the page cache. */
     pPager->nHit++;
     page_ref(pPg);
   }
@@ -2437,10 +2485,12 @@
   */
   pPg = DATA_TO_PGHDR(pData);
   assert( pPg->nRef>0 );
   pPg->nRef--;
   REFINFO(pPg);
+
+  CHECK_PAGE(pPg);
 
   /* When the number of references to a page reach 0, call the
   ** destructor and add the page to the freelist.
   */
   if( pPg->nRef==0 ){
@@ -2625,10 +2675,12 @@
   if( pPager->readOnly ){
     return SQLITE_PERM;
   }
 
   assert( !pPager->setMaster );
+
+  CHECK_PAGE(pPg);
 
   /* Mark the page as dirty.  If the page has already been written
   ** to the journal then we can return right away.
   */
   pPg->dirty = 1;
@@ -2829,10 +2881,13 @@
       ** corruption during the next transaction.
       */
     }else{
       TRACE3("DONT_WRITE page %d of %d\n", pgno, PAGERID(pPager));
       pPg->dirty = 0;
+#ifdef SQLITE_CHECK_PAGES
+      pPg->pageHash = pager_pagehash(pPg);
+#endif
     }
   }
 }
 
 /*