Add {start,end}with_lower methods to StringRef.

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

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193706 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 53 insertions, 5 deletions

diff --git a/include/llvm/ADT/StringRef.h b/include/llvm/ADT/StringRef.h
index fd5b28e..ec0c284 100644
--- a/include/llvm/ADT/StringRef.h
+++ b/include/llvm/ADT/StringRef.h
@@ -210,12 +210,18 @@ namespace llvm {
              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
     /// @{
diff --git a/lib/Support/StringRef.cpp b/lib/Support/StringRef.cpp
index ee49ca8..bfae754 100644
--- a/lib/Support/StringRef.cpp
+++ b/lib/Support/StringRef.cpp
@@ -37,20 +37,39 @@ static bool ascii_isdigit(char x) {
   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 (int Res = ascii_strncasecmp(Data, RHS.Data, min(Length, RHS.Length)))
+    return Res;
   if (Length == RHS.Length)
     return 0;
   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) {
diff --git a/unittests/ADT/StringRefTest.cpp b/unittests/ADT/StringRefTest.cpp
index 07fba49..88691ae 100644
--- a/unittests/ADT/StringRefTest.cpp
+++ b/unittests/ADT/StringRefTest.cpp
@@ -61,6 +61,9 @@ TEST(StringRefTest, StringOps) {
   EXPECT_EQ( 0, StringRef("AaB").compare_lower("aab"));
   EXPECT_EQ( 1, StringRef("AaB").compare_lower("AAA"));
   EXPECT_EQ(-1, StringRef("AaB").compare_lower("aaBb"));
+  EXPECT_EQ(-1, StringRef("AaB").compare_lower("bb"));
+  EXPECT_EQ( 1, StringRef("aaBb").compare_lower("AaB"));
+  EXPECT_EQ( 1, StringRef("bb").compare_lower("AaB"));
   EXPECT_EQ( 1, StringRef("AaB").compare_lower("aA"));
   EXPECT_EQ( 1, StringRef("\xFF").compare_lower("\1"));
 
@@ -254,6 +257,16 @@ TEST(StringRefTest, StartsWith) {
   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(""));
@@ -263,6 +276,16 @@ TEST(StringRefTest, EndsWith) {
   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'));