fixed saving calc command history

Fixed a bug where the calc command history was not being properly
saved in the history file.  Thanks go to the GitHub user @Vekhir
for both reporting this problem and helping come up with a solution.

Per request, we expanded number of entries to save from 1024 to 4096.

Author: lcn2

CHANGES

@@ -1,3 +1,12 @@
+The following are the changes from calc version 2.16.1.1 to date:
+
+    Fixed a bug where the calc command history was not being properly
+    saved in the history file.  Thanks go to the GitHub user @Vekhir
+    for both reporting this problem and helping come up with a solution.
+
+    Per request, we expanded number of entries to save from 1024 to 4096.
+
+
 The following are the changes from calc version 2.16.1.0 to 2.16.1.1:
 
     Fix compiler warning for `custom/u_pfe.c`.

hist.c

@@ -1,7 +1,7 @@
 /*
  * hist - interactive readline module
  *
- * Copyright (C) 1999-2007,2021-2023  David I. Bell
+ * Copyright (C) 1999-2007,2021-2023,2026  David I. Bell
  *
  * Calc is open software; you can redistribute it and/or modify it under
  * the terms of the version 2.1 of the GNU Lesser General Public License
@@ -1485,7 +1485,7 @@ quit_calc(int UNUSED(ch))
 
 #if defined(USE_READLINE)
 
-#  define HISTORY_LEN (1024) /* number of entries to save */
+#  define HISTORY_LEN (4096) /* number of entries to save */
 
 #  include <readline/readline.h>
 #  include <readline/history.h>
@@ -1574,6 +1574,20 @@ my_stifle_history(void)
     }
 }
 
+/*
+ * close down and complete history and free the calc_history value allocated by initenv().
+ */
+S_FUNC void
+hist_finish(void)
+{
+    /* only save last number of entries */
+    my_stifle_history();
+    if (calc_history != NULL) {
+        free(calc_history);
+        calc_history = NULL;
+    }
+}
+
 int
 hist_init(char *UNUSED(filename))
 {
@@ -1605,7 +1619,8 @@ hist_init(char *UNUSED(filename))
     /* read previous history */
     read_history(calc_history);
 
-    atexit(my_stifle_history);
+    /* setup how history is closed down and synced when exiting */
+    atexit(hist_finish);
 
     return HIST_SUCCESS;
 }

lib_calc.c

@@ -1,7 +1,7 @@
 /*
  * lib_calc - calc link library initialization and shutdown routines
  *
- * Copyright (C) 1999-2007,2018,2021-2023  Landon Curt Noll
+ * Copyright (C) 1999-2007,2018,2021-2023,2026  Landon Curt Noll
  *
  * Calc is open software; you can redistribute it and/or modify it under
  * the terms of the version 2.1 of the GNU Lesser General Public License
@@ -722,10 +722,17 @@ libcalc_call_me_last(void)
         free(shell);
         shell = NULL;
     }
-    if (calc_history != NULL) {
-        free(calc_history);
-        calc_history = NULL;
-    }
+    /*
+     * IMPORT NOTE: Do NOT free calc_history here !!!
+     *
+     * If you do, this will cause the history you have made to be lost!
+     *
+     * FYI In hist.c:
+     *
+     * The hist_finish() function, which is invoked due to a call to
+     * atexit(hist_finish) in hist_init() will take care of freeing
+     * the calc_history storage, if it was allocated in initenv().
+     */
     if (calc_helpdir != NULL) {
         free(calc_helpdir);
         calc_helpdir = NULL;