diff options
Diffstat (limited to 'absl/strings/internal/cord_rep_btree_reader.h')
-rw-r--r-- | absl/strings/internal/cord_rep_btree_reader.h | 58 |
1 files changed, 25 insertions, 33 deletions
diff --git a/absl/strings/internal/cord_rep_btree_reader.h b/absl/strings/internal/cord_rep_btree_reader.h index c19fa43d..66e97f5d 100644 --- a/absl/strings/internal/cord_rep_btree_reader.h +++ b/absl/strings/internal/cord_rep_btree_reader.h @@ -31,9 +31,7 @@ namespace cord_internal { // References to the underlying data are returned as absl::string_view values. // The most typical use case is a forward only iteration over tree data. // The class also provides `Skip()`, `Seek()` and `Read()` methods similar to -// CordRepBtreeNavigator that allow more advanced navigation. The class provides -// a `consumed` property which contains the end offset of the chunk last -// returned to the user which is useful in cord iteration logic. +// CordRepBtreeNavigator that allow more advanced navigation. // // Example: iterate over all data inside a cord btree: // @@ -61,9 +59,9 @@ namespace cord_internal { // absl::string_view sv = reader.Next(); // } // -// It is important to notice that `consumed` represents the end position of the -// last data edge returned to the caller, not the cumulative data returned to -// the caller which can be less in cases of skipping or seeking over data. +// It is important to notice that `remaining` is based on the end position of +// the last data edge returned to the caller, not the cumulative data returned +// to the caller which can be less in cases of skipping or seeking over data. // // For example, consider a cord btree with five data edges: "abc", "def", "ghi", // "jkl" and "mno": @@ -71,14 +69,12 @@ namespace cord_internal { // absl::string_view sv; // CordRepBtreeReader reader; // -// sv = reader.Init(tree); // sv = "abc", reader.consumed() = 3 -// sv = reader.Skip(4); // sv = "hi", reader.consumed() = 9 -// sv = reader.Skip(2); // sv = "l", reader.consumed() = 12 -// sv = reader.Next(); // sv = "mno", reader.consumed() = 15 +// sv = reader.Init(tree); // sv = "abc", remaining = 12 +// sv = reader.Skip(4); // sv = "hi", remaining = 6 +// sv = reader.Skip(2); // sv = "l", remaining = 3 +// sv = reader.Next(); // sv = "mno", remaining = 0 +// sv = reader.Seek(1); // sv = "bc", remaining = 12 // -// In the above example, `reader.consumed()` reflects the data edges iterated -// over or skipped by the reader, not the amount of data 'consumed' by the -// caller. class CordRepBtreeReader { public: using ReadResult = CordRepBtreeNavigator::ReadResult; @@ -98,13 +94,14 @@ class CordRepBtreeReader { // Requires that the current instance is not empty. size_t length() const; - // Returns the end offset of the last navigated to chunk, which represents the - // total bytes 'consumed' relative to the start of the tree. The returned - // value is never zero. For example, initializing a reader with a tree with a - // first data edge of 19 bytes will return `consumed() = 19`. See also the - // class comments on the meaning of `consumed`. - // Requires that the current instance is not empty. - size_t consumed() const; + // Returns the number of remaining bytes available for iteration, which is the + // number of bytes directly following the end of the last chunk returned. + // This value will be zero if we iterated over the last edge in the bound + // tree, in which case any call to Next() or Skip() will return an empty + // string_view reflecting the EOF state. + // Note that a call to `Seek()` resets `remaining` to a value based on the + // end position of the chunk returned by that call. + size_t remaining() const { return remaining_; } // Resets this instance to an empty value. void Reset() { navigator_.Reset(); } @@ -157,7 +154,7 @@ class CordRepBtreeReader { absl::string_view Seek(size_t offset); private: - size_t consumed_; + size_t remaining_ = 0; CordRepBtreeNavigator navigator_; }; @@ -166,23 +163,18 @@ inline size_t CordRepBtreeReader::length() const { return btree()->length; } -inline size_t CordRepBtreeReader::consumed() const { - assert(btree() != nullptr); - return consumed_; -} - inline absl::string_view CordRepBtreeReader::Init(CordRepBtree* tree) { assert(tree != nullptr); const CordRep* edge = navigator_.InitFirst(tree); - consumed_ = edge->length; + remaining_ = tree->length - edge->length;; return CordRepBtree::EdgeData(edge); } inline absl::string_view CordRepBtreeReader::Next() { - assert(consumed() < length()); + if (remaining_ == 0) return {}; const CordRep* edge = navigator_.Next(); assert(edge != nullptr); - consumed_ += edge->length; + remaining_ -= edge->length; return CordRepBtree::EdgeData(edge); } @@ -192,23 +184,23 @@ inline absl::string_view CordRepBtreeReader::Skip(size_t skip) { const size_t edge_length = navigator_.Current()->length; CordRepBtreeNavigator::Position pos = navigator_.Skip(skip + edge_length); if (ABSL_PREDICT_FALSE(pos.edge == nullptr)) { - consumed_ = length(); + remaining_ = 0; return {}; } // The combined length of all edges skipped before `pos.edge` is `skip - // pos.offset`, all of which are 'consumed', as well as the current edge. - consumed_ += skip - pos.offset + pos.edge->length; + remaining_ -= skip - pos.offset + pos.edge->length; return CordRepBtree::EdgeData(pos.edge).substr(pos.offset); } inline absl::string_view CordRepBtreeReader::Seek(size_t offset) { const CordRepBtreeNavigator::Position pos = navigator_.Seek(offset); if (ABSL_PREDICT_FALSE(pos.edge == nullptr)) { - consumed_ = length(); + remaining_ = 0; return {}; } absl::string_view chunk = CordRepBtree::EdgeData(pos.edge).substr(pos.offset); - consumed_ = offset + chunk.length(); + remaining_ = length() - offset - chunk.length(); return chunk; } |