Ensure randomly generated rowids never go negative.

FossilOrigin-Name: 631423677bd7043e99987edc633005443125181c

manifest

@@ -1,5 +1,5 @@
-C Do\snot\sclear\sthe\sinternal\s"schema\shas\schanged"\sflag\swhen\sperforming\sa\ssavepoint\srollback.\sThe\sschema\schanges\smay\snot\shave\staken\splace\swithin\sthe\ssavepoint\sbeing\srolled\sback.
-D 2010-08-31T16:25:20
+C Ensure\srandomly\sgenerated\srowids\snever\sgo\snegative.
+D 2010-09-01T02:37:56
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in c599a15d268b1db2aeadea19df2adc3bf2eb6bee
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -222,7 +222,7 @@ F src/update.c 227e6cd512108b84f69421fc6c7aa1b83d60d6e0
 F src/utf.c 1baeeac91707a4df97ccc6141ec0f808278af685
 F src/util.c 5f5f4db4e799224713582bb49124827b16aa8e54
 F src/vacuum.c 241a8386727c1497eba4955933356dfba6ff8c9f
-F src/vdbe.c 41a186c0f29ee2e9fcd8754d7e792540f3c0db40
+F src/vdbe.c 20ef377f7915a7076af6f4c9ffe2f920e34484fa
 F src/vdbe.h 4de0efb4b0fdaaa900cf419b35c458933ef1c6d2
 F src/vdbeInt.h a247bd5448039e83394bf4179975b2ae0092874c
 F src/vdbeapi.c bec07756e1b3ec5cd054ce8d32a80787763fd07e
@@ -851,7 +851,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 7c4f80ad272138cd4ab30455fae6a36498362933
-R 9842f8753de011b5314161323062b619
-U dan
-Z 858a8b145c877bef8fc144001bc5b64b
+P c2a84430d3b6bb53b19af9294973575178290f93
+R dfa25dc2885cfefe1659176091b19b37
+U shaneh
+Z 79cc05c849b02833caa229e781acac58

manifest.uuid

@@ -1 +1 @@
-c2a84430d3b6bb53b19af9294973575178290f93
+631423677bd7043e99987edc633005443125181c

src/vdbe.c

@@ -3719,18 +3719,24 @@ case OP_NewRowid: {           /* out2-prerelease */
       */
       assert( pOp->p3==0 );  /* We cannot be in random rowid mode if this is
                              ** an AUTOINCREMENT table. */
+      /* on the first attempt, simply do one more than previous */
       v = db->lastRowid;
+      v &= (MAX_ROWID>>1); /* ensure doesn't go negative */
+      v++; /* ensure non-zero */
       cnt = 0;
-      do{
-        if( cnt==0 && (v&0xffffff)==v ){
-          v++;
+      while(   ((rc = sqlite3BtreeMovetoUnpacked(pC->pCursor, 0, (u64)v, 0, &res))==SQLITE_OK)
+            && (res==0)
+            && (++cnt<100)){
+        /* collision - try another random rowid */
+        sqlite3_randomness(sizeof(v), &v);
+        if( cnt<5 ){
+          /* try "small" random rowids for the initial attempts */
+          v &= 0xffffff;
         }else{
-          sqlite3_randomness(sizeof(v), &v);
-          if( cnt<5 ) v &= 0xffffff;
+          v &= (MAX_ROWID>>1); /* ensure doesn't go negative */
         }
-        rc = sqlite3BtreeMovetoUnpacked(pC->pCursor, 0, (u64)v, 0, &res);
-        cnt++;
-      }while( cnt<100 && rc==SQLITE_OK && res==0 );
+        v++; /* ensure non-zero */
+      }
       if( rc==SQLITE_OK && res==0 ){
         rc = SQLITE_FULL;   /* IMP: R-38219-53002 */
         goto abort_due_to_error;