Subject: Re: bug#67536: 29.1; Calc mode's math-read-preprocess-string conses unnecessarily

From: Raffael Stocker <[email-masked]>
Date: Fri, 01 Dec 2023 18:34:10 +0100

Eli Zaretskii <[email-masked]> writes:

> Thanks, sounds like a good optimization to me.

Splendid!

I cleaned it up a bit and ran a few tests against the original function
using an empty string, a string without anything to replace and a string
requiring many replacements.  It seems to behave just as the original.

I use cl-flet and (eval-when-compile (require 'cl-lib)).  I hope that is
ok.

Regards,
Raffael

>From b3c055cfb42f45ffe662f4fa24ce7b0104949eb2 Mon Sep 17 00:00:00 2001
From: Raffael Stocker <[email-masked]>
Date: Fri, 1 Dec 2023 18:24:59 +0100
Subject: [PATCH] * lisp/calc/calc-aent.el (math-read-preprocess-string): cons
 less (bug#67536)

Use a temp buffer instead of working on a string.  This function is
called by calc-eval, which in turn is called repeatedly when
re-calculating org-mode tables.  This function is one of the main
bottlenecks there.
---
 lisp/calc/calc-aent.el | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/lisp/calc/calc-aent.el b/lisp/calc/calc-aent.el
index 66ede3295ae..84b580a7033 100644
--- a/lisp/calc/calc-aent.el
+++ b/lisp/calc/calc-aent.el
@@ -27,6 +27,7 @@
 
 (require 'calc)
 (require 'calc-macs)
+(eval-when-compile (require 'cl-lib))
 
 ;; Declare functions which are defined elsewhere.
 (declare-function calc-digit-start-entry "calc" ())
@@ -550,19 +551,17 @@ math-read-subscripts
 ;;;###autoload
 (defun math-read-preprocess-string (str)
   "Replace some substrings of STR by Calc equivalents."
-  (setq str
-        (replace-regexp-in-string (concat "[" math-read-superscripts "]+")
-                                  "^(\\&)" str))
-  (setq str
-        (replace-regexp-in-string (concat "[" math-read-subscripts "]+")
-                                  "_(\\&)" str))
-  (let ((rep-list math-read-replacement-list))
-    (while rep-list
-      (setq str
-            (replace-regexp-in-string (nth 0 (car rep-list))
-                                      (nth 1 (car rep-list)) str))
-      (setq rep-list (cdr rep-list))))
-  str)
+  (with-temp-buffer
+    (cl-flet ((replace-all (regexp replacement)
+                (goto-char 0)
+                (while (re-search-forward regexp nil t)
+                  (replace-match replacement))))
+      (insert str)
+      (replace-all (concat "[" math-read-superscripts "]+") "^(\\&)")
+      (replace-all (concat "[" math-read-subscripts "]+") "_(\\&)")
+      (dolist (rep-elem math-read-replacement-list)
+        (replace-all (car rep-elem) (cadr rep-elem)))
+      (buffer-string))))
 
 ;; The next few variables are local to math-read-exprs (and math-read-expr
 ;; in calc-ext.el), but are set in functions they call.
-- 
2.43.0