ENHANCED: Faster format/3 for binary streams.

This speeds up web servers considerably when sending binary files.

src/prolog/lib/format.pl

@@ -367,8 +367,20 @@ format(Fs, Args) :-
 format(Stream, Fs, Args) :-
         phrase(format_(Fs, Args), Cs),
         (   stream_property(Stream, type(binary)) ->
-            maplist(char_code, Cs, Bytes),
-            maplist(put_byte(Stream), Bytes)
+            % maplist(char_code, Cs, Bytes) is currently a lot slower
+            % than first converting Cs to an atom, and then to codes.
+            % In the future, we can ideally avoid creating an atom here,
+            % since an atom leaves traces in the system.
+            atom_chars(A, Cs),
+            atom_codes(A, Bytes),
+            (   member(NonByte, Bytes), NonByte > 255 ->
+                char_code(Char, NonByte),
+                throw(error(representation_error(Char), format/3))
+            ;   true
+            ),
+            % For binary streams, we use a specialised internal predicate
+            % that uses only a single "write" operation for efficiency.
+            '$put_bytes'(Stream, Bytes)
         ;   maplist(put_char(Stream), Cs)
         ).