more TDB

source/libs/tdb/src/db/tdbBtree.c

@@ -1276,35 +1276,35 @@ static int tdbBtcMoveUpward(SBTC *pBtc) {
 static int tdbBtcMoveTo(SBTC *pBtc, const void *pKey, int kLen, int *pCRst) {
   int          ret;
   SBTree      *pBt;
+  SCell       *pCell;
   SPager      *pPager;
+  SCellDecoder cd = {0};
 
   pBt = pBtc->pBt;
   pPager = pBt->pPager;
 
   if (pBtc->iPage < 0) {
-    ASSERT(pBtc->iPage == -1);
-    ASSERT(pBtc->idx == -1);
-
-    // Move from the root
+    // move from a clear cursor
     ret = tdbPagerFetchPage(pPager, pBt->root, &(pBtc->pPage), tdbBtreeInitPage, pBt);
     if (ret < 0) {
+      // TODO
       ASSERT(0);
-      return -1;
+      return 0;
     }
 
     pBtc->iPage = 0;
-
-    if (TDB_PAGE_TOTAL_CELLS(pBtc->pPage) == 0) {
-      // Current page is empty
-      // ASSERT(TDB_FLAG_IS(TDB_PAGE_FLAGS(pBtc->pPage), TDB_BTREE_ROOT | TDB_BTREE_LEAF));
-      return 0;
+    pBtc->idx = -1;
+    // for empty tree, just return with an invalid position
+    if (TDB_PAGE_TOTAL_CELLS(pBtc->pPage) == 0) return 0;
+  } else {
+    // move upward to a page that the search key is in the range
+    ASSERT(0);
   }
 
+  // search downward to the leaf
   for (;;) {
     int    lidx, ridx, midx, c, nCells;
-      SCell       *pCell;
     SPage *pPage;
-      SCellDecoder cd = {0};
 
     pPage = pBtc->pPage;
     nCells = TDB_PAGE_TOTAL_CELLS(pPage);
@@ -1312,7 +1312,9 @@ static int tdbBtcMoveTo(SBTC *pBtc, const void *pKey, int kLen, int *pCRst) {
     ridx = nCells - 1;
 
     ASSERT(nCells > 0);
+    ASSERT(pBtc->idx == -1);
 
+    // binary search
     for (;;) {
       if (lidx > ridx) break;
 
@@ -1329,20 +1331,19 @@ static int tdbBtcMoveTo(SBTC *pBtc, const void *pKey, int kLen, int *pCRst) {
       // Compare the key values
       c = pBt->kcmpr(pKey, kLen, cd.pKey, cd.kLen);
       if (c < 0) {
-          /* input-key < cell-key */
+        // pKey < cd.pKey
         ridx = midx - 1;
       } else if (c > 0) {
-          /* input-key > cell-key */
+        // pKey > cd.pKey
         lidx = midx + 1;
       } else {
-          /* input-key == cell-key */
+        // pKey == cd.pKey
         break;
       }
     }
 
-      // Move downward or break
-      u8 leaf = TDB_BTREE_PAGE_IS_LEAF(pPage);
-      if (leaf) {
+    // keep search downward or break
+    if (TDB_BTREE_PAGE_IS_LEAF(pPage)) {
       pBtc->idx = midx;
       *pCRst = c;
       break;
@@ -1356,11 +1357,6 @@ static int tdbBtcMoveTo(SBTC *pBtc, const void *pKey, int kLen, int *pCRst) {
     }
   }
 
-  } else {
-    // TODO: Move the cursor from a some position instead of a clear state
-    ASSERT(0);
-  }
-
   return 0;
 }