What do the @ (at symbols) in a terminfo manipulation code mean?

Question

I'm trying to convert a terminfo string from xterm to something that will work with iTerm2 in order to get 24bit colors working in emacs . The investigating and research I've done so far leads me to believe that the terminfo manipulation codes I'm using to set stf24/setb24 are being incorrectly interpreted by iTerm2, so I want to understand what these are doing.

Here are the custom values that emacs requires:

xterm-24bit|xterm with 24-bit direct color mode,
   use=xterm-256color,
   setb24=\E[48:2:%p1%@{65536@}%/%d:%p1%@{256@}%/%@{255@}%&%d:%p1%@{255@}%&%dm,
   setf24=\E[38:2:%p1%@{65536@}%/%d:%p1%@{256@}%/%@{255@}%&%d:%p1%@{255@}%&%dm,
# Use semicolon separators.
xterm-24bits|xterm with 24-bit direct color mode,
   use=xterm-256color,
   setb24=\E[48;2;%p1%@{65536@}%/%d;%p1%@{256@}%/%@{255@}%&%d;%p1%@{255@}%&%dm,
   setf24=\E[38;2;%p1%@{65536@}%/%d;%p1%@{256@}%/%@{255@}%&%d;%p1%@{255@}%&%dm,

I know that the first bit eg \\e[48:2: is the escape code specifying the colour location (in this case background) and the colour format (2 means full 24-bit RGB format requiring 3 control segments). Looking at this documentation 'Supported TERMINFO Manipulation Codes' I know that it is taking a parameter '1' from the stack with %p1 , and performing a few other operations on this ( %/ - division, %& - AND ) but I'm not sure what %@ means or what the numbers in brackets mean %@{65536} , and also what the %dm does at the end. Can anyone assist?

Overall, I believe emacs only passes the one parameter (presumably a single number within 256^3 0-16,777,216), so I think this is somehow breaking it apart into the 3 constituent RGB colours that the terminal needs, but I haven't quite worked out how, and then whether there is an incompatibility and where it lies.

Answer 1

The @ marks are not part of the terminfo description; they are used in the original texinfo file to prevent the curly braces from being interpreted. What you're reading is cut/paste from someone who didn't understand either part of the markup...

Without the @ marks, you'll have constants, eg, %{65536} used in arithmetic.

The "%dm on the end" is just the third parameter, ie, the blue value in RGB (note that there are two other "%d" marks), with the final character "m".