Index: include/clang/AST/ASTContext.h
===================================================================
--- include/clang/AST/ASTContext.h
+++ include/clang/AST/ASTContext.h
@@ -1489,6 +1489,10 @@
   /// <stddef.h>. Pointer - pointer requires this (C99 6.5.6p9).
   QualType getPointerDiffType() const;
 
+  /// \brief Return the unique unsigned counterpart of 
+  /// "ptrdiff_t" integer type.
+  QualType getUnsignedPointerDiffType() const;
+
   /// \brief Return the unique type for "pid_t" defined in
   /// <sys/types.h>. We need this to compute the correct type for vfork().
   QualType getProcessIDType() const;
Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -248,6 +248,9 @@
   IntType getPtrDiffType(unsigned AddrSpace) const {
     return AddrSpace == 0 ? PtrDiffType : getPtrDiffTypeV(AddrSpace);
   }
+  IntType getUnsignedPtrDiffType(unsigned AddrSpace) const {
+    return getCorrespondingUnsignedType(getPtrDiffType(AddrSpace));
+  }
   IntType getIntPtrType() const { return IntPtrType; }
   IntType getUIntPtrType() const {
     return getCorrespondingUnsignedType(IntPtrType);
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -4571,6 +4571,12 @@
   return getFromTargetType(Target->getPtrDiffType(0));
 }
 
+/// getUnsignedPointerDiffType - Return the unique unsigned counterpart of
+// "ptrdiff_t" integer type.
+QualType ASTContext::getUnsignedPointerDiffType() const {
+  return getFromTargetType(Target->getUnsignedPtrDiffType(0));
+}
+
 /// \brief Return the unique type for "pid_t" defined in
 /// <sys/types.h>. We need this to compute the correct type for vfork().
 QualType ASTContext::getProcessIDType() const {