remove manual math

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/convert.cpp

@@ -1145,7 +1145,7 @@ void Converter::cnvXmpGPSCoord(const char* from, const char* to) {
   char sep1 = '\0';
   char sep2 = '\0';
 
-  value.erase(value.length() - 1);
+  value.pop_back();
 
   std::istringstream in(value);
 

src/futils.cpp

@@ -264,7 +264,7 @@ void Uri::Decode(Uri& uri) {
 Uri Uri::Parse(const std::string& uri) {
   Uri result;
 
-  if (!uri.length())
+  if (uri.empty())
     return result;
 
   auto uriEnd = uri.end();
@@ -320,7 +320,7 @@ Uri Uri::Parse(const std::string& uri) {
     auto portEnd = (pathStart != uriEnd) ? pathStart : queryStart;
     result.Port = std::string(hostEnd, portEnd);
   }
-  if (!result.Port.length() && result.Protocol == "http")
+  if (result.Port.empty() && result.Protocol == "http")
     result.Port = "80";
 
   // path

src/jpgimage.cpp

@@ -200,8 +200,8 @@ void JpegBase::readMetadata() {
       // the first one (most jpegs only have one anyway). Comments
       // are simple single byte ISO-8859-1 strings.
       comment_.assign(buf.c_str(2), size - 2);
-      while (comment_.length() && comment_.at(comment_.length() - 1) == '\0') {
+      while (!comment_.empty() && comment_.back() == '\0') {
-        comment_.erase(comment_.length() - 1);
+        comment_.pop_back();
       }
       --search;
     } else if (marker == app2_ && size >= 13  // prevent out-of-bounds read in memcmp on next line