Add the sqlite3_snapshot_cmp() interface (available only with

SQLITE_ENABLE_SNAPSHOT).

FossilOrigin-Name: 7e7289655185e7643ead6d685922528bc4d9e0ae

1 files changed, 17 insertions, 0 deletions

diff --git a/src/wal.c b/src/wal.c
index bbac1bd6d..98b46be80 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -3399,6 +3399,23 @@ int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){
 void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){
   pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
 }
+
+/* 
+** Return a +ve value if snapshot p1 is newer than p2. A -ve value if
+** p1 is older than p2 and zero if p1 and p2 are the same snapshot.
+*/
+int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){
+  WalIndexHdr *pHdr1 = (WalIndexHdr*)p1;
+  WalIndexHdr *pHdr2 = (WalIndexHdr*)p2;
+
+  /* aSalt[0] is a copy of the value stored in the wal file header. It
+  ** is incremented each time the wal file is restarted.  */
+  if( pHdr1->aSalt[0]<pHdr2->aSalt[0] ) return -1;
+  if( pHdr1->aSalt[0]>pHdr2->aSalt[0] ) return +1;
+  if( pHdr1->mxFrame<pHdr2->mxFrame ) return -1;
+  if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1;
+  return 0;
+}
 #endif /* SQLITE_ENABLE_SNAPSHOT */
 
 #ifdef SQLITE_ENABLE_ZIPVFS