[PATCH] Add {start,end}with_lower methods to StringRef.

[Rui Ueyama]

startswith_lower is ocassionally useful and I think worth adding.
endwith_lower is added for completeness.

http://llvm-reviews.chandlerc.com/D2041

Files:
  include/llvm/ADT/StringRef.h
  lib/Support/StringRef.cpp
  unittests/ADT/StringRefTest.cpp

Index: include/llvm/ADT/StringRef.h
===================================================================
--- include/llvm/ADT/StringRef.h
+++ include/llvm/ADT/StringRef.h
@@ -210,12 +210,18 @@
              compareMemory(Data, Prefix.Data, Prefix.Length) == 0;
     }
 
+    /// Check if this string starts with the given \p Prefix, ignoring case.
+    bool startswith_lower(StringRef Prefix) const;
+
     /// Check if this string ends with the given \p Suffix.
     bool endswith(StringRef Suffix) const {
       return Length >= Suffix.Length &&
         compareMemory(end() - Suffix.Length, Suffix.Data, Suffix.Length) == 0;
     }
 
+    /// Check if this string ends with the given \p Suffix, ignoring case.
+    bool endswith_lower(StringRef Suffix) const;
+
     /// @}
     /// @name String Searching
     /// @{
Index: lib/Support/StringRef.cpp
===================================================================
--- lib/Support/StringRef.cpp
+++ lib/Support/StringRef.cpp
@@ -37,20 +37,37 @@
   return x >= '0' && x <= '9';
 }
 
-/// compare_lower - Compare strings, ignoring case.
-int StringRef::compare_lower(StringRef RHS) const {
-  for (size_t I = 0, E = min(Length, RHS.Length); I != E; ++I) {
-    unsigned char LHC = ascii_tolower(Data[I]);
-    unsigned char RHC = ascii_tolower(RHS.Data[I]);
+// strncasecmp() is not available on non-POSIX systems, so define an
+// alternative function here.
+static int ascii_strncasecmp(const char *LHS, const char *RHS, size_t Length) {
+  for (size_t I = 0; I < Length; ++I) {
+    unsigned char LHC = ascii_tolower(LHS[I]);
+    unsigned char RHC = ascii_tolower(RHS[I]);
     if (LHC != RHC)
       return LHC < RHC ? -1 : 1;
   }
+  return 0;
+}
 
+/// compare_lower - Compare strings, ignoring case.
+int StringRef::compare_lower(StringRef RHS) const {
   if (Length == RHS.Length)
-    return 0;
+    return ascii_strncasecmp(Data, RHS.Data, Length);
   return Length < RHS.Length ? -1 : 1;
 }
 
+/// Check if this string starts with the given \p Prefix, ignoring case.
+bool StringRef::startswith_lower(StringRef Prefix) const {
+  return Length >= Prefix.Length &&
+      ascii_strncasecmp(Data, Prefix.Data, Prefix.Length) == 0;
+}
+
+/// Check if this string ends with the given \p Suffix, ignoring case.
+bool StringRef::endswith_lower(StringRef Suffix) const {
+  return Length >= Suffix.Length &&
+      ascii_strncasecmp(end() - Suffix.Length, Suffix.Data, Suffix.Length) == 0;
+}
+
 /// compare_numeric - Compare strings, handle embedded numbers.
 int StringRef::compare_numeric(StringRef RHS) const {
   for (size_t I = 0, E = min(Length, RHS.Length); I != E; ++I) {
Index: unittests/ADT/StringRefTest.cpp
===================================================================
--- unittests/ADT/StringRefTest.cpp
+++ unittests/ADT/StringRefTest.cpp
@@ -253,14 +253,34 @@
   EXPECT_FALSE(Str.startswith("hi"));
 }
 
+TEST(StringRefTest, StartsWithLower) {
+  StringRef Str("heLLo");
+  EXPECT_TRUE(Str.startswith_lower(""));
+  EXPECT_TRUE(Str.startswith_lower("he"));
+  EXPECT_TRUE(Str.startswith_lower("hell"));
+  EXPECT_TRUE(Str.startswith_lower("HELlo"));
+  EXPECT_FALSE(Str.startswith_lower("helloworld"));
+  EXPECT_FALSE(Str.startswith_lower("hi"));
+}
+
 TEST(StringRefTest, EndsWith) {
   StringRef Str("hello");
   EXPECT_TRUE(Str.endswith("lo"));
   EXPECT_FALSE(Str.endswith("helloworld"));
   EXPECT_FALSE(Str.endswith("worldhello"));
   EXPECT_FALSE(Str.endswith("so"));
 }
 
+TEST(StringRefTest, EndsWithLower) {
+  StringRef Str("heLLo");
+  EXPECT_TRUE(Str.endswith_lower(""));
+  EXPECT_TRUE(Str.endswith_lower("lo"));
+  EXPECT_TRUE(Str.endswith_lower("LO"));
+  EXPECT_TRUE(Str.endswith_lower("ELlo"));
+  EXPECT_FALSE(Str.endswith_lower("helloworld"));
+  EXPECT_FALSE(Str.endswith_lower("hi"));
+}
+
 TEST(StringRefTest, Find) {
   StringRef Str("hello");
   EXPECT_EQ(2U, Str.find('l'));
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