From 02e26074dc1bd72a2858a89ba7242bdca06f40db Mon Sep 17 00:00:00 2001
From: Leo Liu <sdl.web@gmail.com>
Date: Mon, 20 Apr 2020 09:50:07 +0800
Subject: [PATCH] Generate ID and SERIAL for pid according to spec

http://erlang.org/doc/apps/erts/erl_ext_dist.html#pid_ext

Fixes #68.
---
 elisp/erl.el | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/elisp/erl.el b/elisp/erl.el
index d29787f..15b66b2 100644
--- a/elisp/erl.el
+++ b/elisp/erl.el
@@ -44,21 +44,31 @@
             :named
             (:initial-offset 1)         ; make room for erl-tag (TYPE)
             (:constructor nil)          ; no default constructor
-            (:constructor %make-erl-local-pid (&optional (id (incf erl-pid-counter))
-                                                         (node erl-node-name)
-                                                         (serial 0)
-                                                         (creation 0))))
+            (:constructor %make-erl-local-pid
+                          (id serial &optional (node erl-node-name) (creation 0))))
   node id serial creation)
 
-(defun make-erl-local-pid (&optional id)
+(defun make-erl-local-pid ()
   "Make a node-local pid."
-  (let ((pid (if id
-                 (%make-erl-local-pid id)
-               (%make-erl-local-pid))))
+  (let ((pid (apply #'%make-erl-local-pid
+                    (erl-get-counter erl-pid-counter))))
     ;; Tag the first element of the pid
     (setf (elt pid 0) erl-tag)
     pid))
 
+(defun erl-get-counter (counter)
+  "Get and then advance counter."
+  (cl-macrolet ((modf (place y) `(cl-callf mod ,place ,y))
+                (roundf (place) `(cl-callf round ,place)))
+    (cl-labels ((increment (cells)
+                  (cl-incf (caar cells))
+                  (modf (caar cells) (cdar cells))
+                  ;; Be defensive; `mod' may return float so round it off.
+                  (roundf (caar cells))
+                  (when (and cells (zerop (caar cells)))
+                    (increment (cdr cells)))))
+      (prog1 (mapcar #'car counter) (increment counter)))))
+
 ;; Global book keeping state
 
 (defun erl-determine-hostname ()
@@ -70,19 +80,20 @@
           (match-string 0 fqdn)
         (error "erl: Can't determine hostname.")))))
 
+;; (NUM SERIAL)
+(defvar erl-pid-counter '((0 . #x8000) (0 . #x2000))
+  "Counters for PIDs.")
+
 (defvar erl-node-name
   (intern (format "distel_%S@%s" (emacs-pid) (erl-determine-hostname)))
   "Node name for Emacs.")
 
-(defconst erl-null-pid (make-erl-local-pid 0)
+(defconst erl-null-pid (make-erl-local-pid)
   "\"Null process\", the /dev/null of erl processes.
 Any messages sent to this process are quietly discarded.  When code
 isn't running in the buffer of a particular process, it's running as
 the null process.")
 
-(defvar erl-pid-counter 0
-  "Counter for PIDs.")
-
 (defvar erl-process-buffer-alist nil
   "Automatically-maintained association list of (PID-ID . BUFFER)
 mappings for local processes.")