https://github.com/NixOS/nixpkgs/commit/92d99c521b2c02fa645b3b993ac4bbaf49e43ddd

diff -ur a/pic2plot/gram.cc b/pic2plot/gram.cc
--- a/pic2plot/gram.cc	2000-06-28 00:23:21.000000000 -0400
+++ b/pic2plot/gram.cc	2023-09-07 22:59:47.004460065 -0400
@@ -1229,9 +1229,9 @@
      char *from;
      unsigned int count;
 {
-  register char *f = from;
-  register char *t = to;
-  register int i = count;
+  char *f = from;
+  char *t = to;
+  int i = count;

   while (i-- > 0)
     *t++ = *f++;
@@ -1244,9 +1244,9 @@
 static void
 __yy_memcpy (char *to, char *from, unsigned int count)
 {
-  register char *t = to;
-  register char *f = from;
-  register int i = count;
+  char *t = to;
+  char *f = from;
+  int i = count;

   while (i-- > 0)
     *t++ = *f++;
@@ -1289,10 +1289,10 @@
 yyparse(YYPARSE_PARAM_ARG)
      YYPARSE_PARAM_DECL
 {
-  register int yystate;
-  register int yyn;
-  register short *yyssp;
-  register YYSTYPE *yyvsp;
+  int yystate;
+  int yyn;
+  short *yyssp;
+  YYSTYPE *yyvsp;
   int yyerrstatus;	/*  number of tokens to shift before error messages enabled */
   int yychar1 = 0;		/*  lookahead token as an internal (translated) token number */