added functions Loop::common_prefix() and isame(char, char)

use common_prefix() in error message about wrong number of values in loop

include/gemmi/cif.hpp

@@ -259,7 +259,9 @@ template<> struct Action<rules::loop> {
     assert(last_item.type == ItemType::Loop);
     const Loop& loop = last_item.loop;
     if (loop.values.size() % loop.tags.size() != 0)
-      throw pegtl::parse_error("Wrong number of values in the loop", in);
+      throw pegtl::parse_error(
+          "Wrong number of values in loop " + loop.common_prefix() + "*",
+          in);
   }
 };
 

include/gemmi/cifdoc.hpp

@@ -184,6 +184,19 @@ struct Loop {
   }
 
   void set_all_values(std::vector<std::vector<std::string>> columns);
+
+  std::string common_prefix() const {
+    if (tags.empty())
+      return {};
+    size_t len = tags[0].size();
+    for (auto it = tags.begin() + 1; it != tags.end(); ++it)
+      for (size_t n = 0; n != len; ++n)
+        if (!isame(tags[0][n], (*it)[n])) {
+          len = n;
+          break;
+        }
+    return tags[0].substr(0, len);
+  }
 };
 
 

include/gemmi/util.hpp

@@ -72,20 +72,23 @@ inline std::string to_upper(std::string str) {
   return str;
 }
 
-// Case-insensitive comparisons. The second arg must be lowercase.
-
-inline bool iequal(const std::string& str, const std::string& low) {
-  return str.length() == low.length() &&
-         std::equal(std::begin(low), std::end(low), str.begin(),
-                    [](char c1, char c2) { return c1 == lower(c2); });
+// case-insensitive character comparison
+inline bool isame(char a, char b) {
+  return a == b || ((a^b) == 0x20 && (a|0x20) >= 'a' && (a|0x20) <= 'z');
 }
 
+// Case-insensitive comparisons. The second arg must be lowercase.
+
 inline bool iequal_from(const std::string& str, size_t offset, const std::string& low) {
   return str.length() == low.length() + offset &&
          std::equal(std::begin(low), std::end(low), str.begin() + offset,
                     [](char c1, char c2) { return c1 == lower(c2); });
 }
 
+inline bool iequal(const std::string& str, const std::string& low) {
+  return iequal_from(str, 0, low);
+}
+
 inline bool istarts_with(const std::string& str, const std::string& prefix) {
   return str.length() >= prefix.length() &&
          std::equal(std::begin(prefix), std::end(prefix), str.begin(),