add ""_lcase to hash lowercase-only strings more efficiently.

src/string_case.hh

@@ -1,4 +1,6 @@
 // Defines an operator""_case that allows string literals in case labels:
+// ""_case generates a guaranteed unique hash for all ASCII strings up to 9 characters
+// ""_lcase generates a guaranteed unique hash for all lowercase letter strings up to 12 characters
 //
 //  switch( case_hash(s) )
 //  {
@@ -18,6 +20,13 @@ unsigned long long frobbel(unsigned long long u)
 	return (u*131) ^ (u>>51);
 }
 
+// for lowercase letters only:
+constexpr inline
+unsigned long long lfrobbel(unsigned long long u)
+{
+	return (u*29);
+}
+
 
 constexpr inline
 unsigned long long case_hash(const char* begin, const char* end)
@@ -25,12 +34,24 @@ unsigned long long case_hash(const char* begin, const char* end)
 	return begin==end ? 0 : frobbel( ((unsigned char)(begin[0])+1) + frobbel(case_hash(begin+1, end)) );
 }
 
+constexpr inline
+unsigned long long lcase_hash(const char* begin, const char* end)
+{
+	return begin==end ? 0 : lfrobbel( ((unsigned char)(begin[0])) + lfrobbel(lcase_hash(begin+1, end)) );
+}
+
 constexpr inline
 unsigned long long operator"" _case (const char* s, size_t len)
 {
 	return case_hash(s, s+len);
 }
 
+constexpr inline
+unsigned long long operator"" _lcase (const char* s, size_t len)
+{
+	return lcase_hash(s, s+len);
+}
+
 
 inline
 unsigned long long case_hash( const char* zero_terminated_string )
@@ -38,10 +59,22 @@ unsigned long long case_hash( const char* zero_terminated_string )
 	return case_hash( zero_terminated_string, zero_terminated_string + strlen(zero_terminated_string) );
 }
 
+inline
+unsigned long long lcase_hash( const char* zero_terminated_string )
+{
+	return lcase_hash( zero_terminated_string, zero_terminated_string + strlen(zero_terminated_string) );
+}
+
 inline
 unsigned long long case_hash( const std::string& s)
 {
     return case_hash( s.data(), s.data()+s.size() );
 }
 
+inline
+unsigned long long lcase_hash( const std::string& s)
+{
+    return lcase_hash( s.data(), s.data()+s.size() );
+}
+
 #endif // PEP_MIME_STRING_CASE_HH