[PATCH] [RFC] Introduce MemoryBuffer::getSlice.

[Peter Collingbourne]

Hi rafael,

http://reviews.llvm.org/D4394

Files:
  include/llvm/Support/MemoryBuffer.h
  lib/Support/MemoryBuffer.cpp

Index: include/llvm/Support/MemoryBuffer.h
===================================================================
--- include/llvm/Support/MemoryBuffer.h
+++ include/llvm/Support/MemoryBuffer.h
@@ -134,6 +134,13 @@
                                         std::unique_ptr<MemoryBuffer> &Result,
                                         int64_t FileSize = -1);
 
+  /// \brief Returns a slice of the given MemoryBuffer, to which ownership is
+  /// transferred. Note that the slice must be null terminated if
+  /// RequiresNullTerminator is true.
+  static MemoryBuffer *getSlice(std::unique_ptr<MemoryBuffer> Underlying,
+                                uint64_t Offset, uint64_t Len,
+                                bool RequiresNullTerminator);
+
   //===--------------------------------------------------------------------===//
   // Provided for performance analysis.
   //===--------------------------------------------------------------------===//
Index: lib/Support/MemoryBuffer.cpp
===================================================================
--- lib/Support/MemoryBuffer.cpp
+++ lib/Support/MemoryBuffer.cpp
@@ -168,6 +168,45 @@
 
 
 //===----------------------------------------------------------------------===//
+// MemoryBufferSlice implementation.
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// MemoryBufferSlice - slice of an owned underlying MemoryBuffer.
+class MemoryBufferSlice : public MemoryBuffer {
+  std::unique_ptr<MemoryBuffer> Underlying;
+
+public:
+  MemoryBufferSlice(std::unique_ptr<MemoryBuffer> U, uint64_t Offset,
+                    uint64_t Len, bool RequiresNullTerminator)
+      : Underlying(std::move(U)) {
+    init(Underlying->getBufferStart() + Offset,
+         Underlying->getBufferStart() + Offset + Len, RequiresNullTerminator);
+  }
+
+  const char *getBufferIdentifier() const override {
+    return Underlying->getBufferIdentifier();
+  }
+
+  BufferKind getBufferKind() const override {
+    return Underlying->getBufferKind();
+  }
+};
+}
+
+/// getSlice - returns a slice of the given MemoryBuffer, to which ownership is
+/// transferred. Note that the slice must be null terminated if
+/// RequiresNullTerminator is true!
+MemoryBuffer *MemoryBuffer::getSlice(std::unique_ptr<MemoryBuffer> Underlying,
+                                     uint64_t Offset, uint64_t Len,
+                                     bool RequiresNullTerminator) {
+  assert(Offset + Len < Underlying->getBufferSize());
+  return new MemoryBufferSlice(std::move(Underlying), Offset, Len,
+                               RequiresNullTerminator);
+}
+
+
+//===----------------------------------------------------------------------===//
 // MemoryBuffer::getFile implementation.
 //===----------------------------------------------------------------------===//
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