move StringPiece to separate file

common/string_piece.h

@@ -0,0 +1,49 @@
+#ifndef COMMON_STRING_PIECE_H
+#define COMMON_STRING_PIECE_H
+
+class Print;
+struct StringPiece {
+  StringPiece(const char* s) : str(s), len(strlen(s)) {}
+  StringPiece(const char* s, size_t l) : str(s), len(l) {}
+  StringPiece(const char* begin, const char* end) : str(begin), len(end >= begin ? end - begin : 0) {}
+  StringPiece() : str(0), len(0) {}
+  int cmp(const StringPiece& other) const {
+    const char* a = str;
+    const char* b = other.str;
+    size_t l = 0;
+    while (true) {
+      if (l == len && l == other.len) return 0;
+      if (l == len) return -1;
+      if (l == other.len) return 1;
+      char A = toLower(*a);
+      char B = toLower(*b);
+      if (A != B) return A < B ? -1 : 1;
+      a++;
+      b++;
+      l++;
+    }
+  }
+  bool operator<(const StringPiece& other) const { return cmp(other) < 0; }
+  bool operator>(const StringPiece& other) const { return cmp(other) > 0; }
+  bool operator<=(const StringPiece& other) const { return cmp(other) <= 0; }
+  bool operator>=(const StringPiece& other) const { return cmp(other) <= 0; }
+  bool operator==(const StringPiece& other) const { return cmp(other) == 0; }
+  bool operator!=(const StringPiece& other) const { return cmp(other) != 0; }
+  char operator[](size_t x) const { return str[x]; }
+  explicit operator bool() const { return str != nullptr && len != 0; }
+
+  void printTo(Print& p);
+  void paste(char* to) const { memcpy(to, str, len); }
+
+  bool contains(char c) const {
+    for (size_t i = 0; i < len; i++) {
+      if (str[i] == c) return true;
+    }
+    return false;
+  }
+
+  const char* str;
+  size_t len;
+};
+
+#endif