Add a new API seek for the Cursor class in the DataExtractor.cpp

Summary:

add a new API seek for the Cursor class in the DataExtractor.cpp

Reviewers: James Henderson, Fangrui Song

Differential Revision: https://reviews.llvm.org/D109603

Author: diggerlin

llvm/include/llvm/Support/DataExtractor.h

@@ -70,6 +70,9 @@ class DataExtractor {
     /// the position of the Cursor before the first error was encountered.
     uint64_t tell() const { return Offset; }
 
+    /// Set the cursor to the new offset. This does not impact the error state.
+    void seek(uint64_t NewOffSet) { Offset = NewOffSet; }
+
     /// Return error contained inside this Cursor, if any. Clears the internal
     /// Cursor state.
     Error takeError() { return std::move(Err); }

llvm/unittests/Support/DataExtractorTest.cpp

@@ -177,6 +177,18 @@ TEST(DataExtractorTest, Cursor_tell) {
   consumeError(C.takeError());
 }
 
+TEST(DataExtractorTest, Cursor_seek) {
+  DataExtractor::Cursor C(5);
+
+  C.seek(3);
+  EXPECT_EQ(3u, C.tell());
+
+  C.seek(8);
+  EXPECT_EQ(8u, C.tell());
+
+  EXPECT_THAT_ERROR(C.takeError(), Succeeded());
+}
+
 TEST(DataExtractorTest, Cursor_takeError) {
   DataExtractor DE(StringRef("AB"), false, 8);
   DataExtractor::Cursor C(0);