add case insensitive string compare

ostd/string.hh

@@ -8,6 +8,7 @@
 
 #include <stdio.h>
 #include <stddef.h>
+#include <ctype.h>
 
 #include "ostd/utility.hh"
 #include "ostd/range.hh"
@@ -184,6 +185,21 @@ diffsize:
         return (s1 < s2) ? -1 : ((s1 > s2) ? 1 : 0);
     }
 
+    int case_compare(CharRangeBase<T const> s) const {
+        ostd::Size s1 = size(), s2 = s.size();
+        if (!s1 || !s2) {
+            goto diffsize;
+        }
+        for (ostd::Size i = 0, ms = ostd::min(s1, s2); i < ms; ++i) {
+            int d = toupper(p_beg[i]) - toupper(s[i]);
+            if (d) {
+                return d;
+            }
+        }
+diffsize:
+        return (s1 < s2) ? -1 : ((s1 > s2) ? 1 : 0);
+    }
+
     template<typename R>
     EnableIf<IsOutputRange<R>, Size> copy(R &&orange, Size n = -1) {
         return orange.put_n(data(), ostd::min(n, size()));
@@ -613,6 +629,10 @@ public:
         return iter().compare(r);
     }
 
+    int case_compare(ConstRange r) const {
+        return iter().case_compare(r);
+    }
+
     Range iter() {
         return Range(p_buf.first(), size());
     }