Avoid wcwidth(), wcrtomb() and mbrtowc() on ASCII/ISO8859-1 characters.

ASCII <-> UTF has trivial mappings.  Avoid wcrtomb() and mbrtowc().

ISO-8859-1 is all narrow characters, and cheap to test for.  It might
be possible to cheaply test other popular UTF blocks and/or planes as
well.

These two changes get 2-3x faster input processing on Linux and
FreeBSD.  Performance improvement in actual usage is more modest but
still significant.

src/terminal/parser.cc

@@ -80,10 +80,15 @@ void Parser::UTF8Parser::input( char c, Actions &ret )
 {
   assert( buf_len < BUF_SIZE );
 
+  /* 1-byte UTF-8 character, aka ASCII?  Cheat. */
+  if ( buf_len == 0 && static_cast<unsigned char>(c) <= 0x7f ) {
+    parser.input( static_cast<wchar_t>(c), ret );
+    return;
+  }
+
   buf[ buf_len++ ] = c;
 
   /* This function will only work in a UTF-8 locale. */
-
   wchar_t pwc;
   mbstate_t ps = mbstate_t();
 

src/terminal/terminal.cc

@@ -61,7 +61,13 @@ void Emulator::print( const Parser::Print *act )
 {
   assert( act->char_present );
 
-  int chwidth = act->ch == L'\0' ? -1 : wcwidth( act->ch );
+  const wchar_t ch = act->ch;
+
+  /*
+   * Check for printing ISO 8859-1 first, it's a cheap way to detect
+   * some common narrow characters.
+   */
+  const int chwidth = ch == L'\0' ? -1 : ( Cell::isprint_iso8859_1( ch ) ? 1 : wcwidth( ch ));
 
   Cell *this_cell = fb.get_mutable_cell();
 
@@ -100,7 +106,7 @@ void Emulator::print( const Parser::Print *act )
     }
 
     fb.reset_cell( this_cell );
-    this_cell->append( act->ch );
+    this_cell->append( ch );
     this_cell->width = chwidth;
     fb.apply_renditions_to_cell( this_cell );
 
@@ -134,7 +140,7 @@ void Emulator::print( const Parser::Print *act )
       }
       if ( combining_cell->contents.size() < 32 ) {
 	/* seems like a reasonable limit on combining characters */
-	combining_cell->append( act->ch );
+	combining_cell->append( ch );
       }
       act->handled = true;
     }

src/terminal/terminalframebuffer.h

@@ -126,8 +126,19 @@ namespace Terminal {
 
     bool compare( const Cell &other ) const;
 
-    static void append_to_str( std::string &dest, const wchar_t c )
+    // Is this a printing ISO 8859-1 character?
+    static bool isprint_iso8859_1( const wchar_t c )
     {
+      return ( c <= 0xff && c >= 0xa0 ) || ( c <= 0x7e && c >= 0x20 );
+    }
+
+   static void append_to_str( std::string &dest, const wchar_t c )
+    {
+      /* ASCII?  Cheat. */
+      if ( static_cast<uint32_t>(c) <= 0x7f ) {
+	dest.push_back( static_cast<char>(c) );
+	return;
+      }
       static mbstate_t ps = mbstate_t();
       char tmp[MB_LEN_MAX];
       size_t ignore = wcrtomb(NULL, 0, &ps);
@@ -138,6 +149,11 @@ namespace Terminal {
 
     void append( const wchar_t c )
     {
+      /* ASCII?  Cheat. */
+      if ( static_cast<uint32_t>(c) <= 0x7f ) {
+	contents.push_back( static_cast<char>(c) );
+	return;
+      }
       static mbstate_t ps = mbstate_t();
       char tmp[MB_LEN_MAX];
       size_t ignore = wcrtomb(NULL, 0, &ps);