[gnumeric] C: Avoid some undefined behaviour problems.

[Morten Welinder <mortenw src gnome org>]

commit a32f4c9bcc55cb07aa4e273fc91a1d73d584fbab
Author: Morten Welinder <terra gnome org>
Date:   Wed May 5 00:01:21 2021 -0400

    C: Avoid some undefined behaviour problems.
    
    memcpy(dst, NULL, 0)   is no good
    integer overflow also isn't good

 ChangeLog       |  8 ++++++++
 NEWS            |  1 +
 src/rangefunc.c |  2 +-
 src/workbook.c  | 11 ++++++-----
 4 files changed, 16 insertions(+), 6 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 0ecf92bed..08c27ad00 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2021-05-05  Morten Welinder  <terra gnome org>
+
+       * src/workbook.c (workbook_cells): Avoid undefined behaviour.
+
+2021-05-04  Morten Welinder  <terra gnome org>
+
+       * src/rangefunc.c (gnm_range_adtest): Avoid integer overflow.
+
 2021-03-29  Morten Welinder  <terra gnome org>
 
        * src/hlink.h (GNM_HLINK_EXTERNAL_TYPE): Add checker macro.
diff --git a/NEWS b/NEWS
index 04c2127ba..faad6163d 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,7 @@ Morten:
        * Introspection fixes.
        * Improve CELL("format",...)  [#576]
        * wk4 import improvements.  (For no good reason.)
+       * Fix some -fsanitize=undefined problems.
 
 --------------------------------------------------------------------------
 Gnumeric 1.12.49
diff --git a/src/rangefunc.c b/src/rangefunc.c
index 97a699fa8..04db922a9 100644
--- a/src/rangefunc.c
+++ b/src/rangefunc.c
@@ -490,7 +490,7 @@ gnm_range_adtest    (gnm_float const *xs, int n, gnm_float *pvalue,
                total = - n - total/n;
                g_free (ys);
 
-               total *= (1 + 0.75 / n + 2.25 / (n * n));
+               total *= (1 + 0.75 / n + 2.25 / ((gnm_float)n * n));
                if (total < 0.2)
                        p = 1. - gnm_exp (-13.436 + 101.14 * total - 223.73 * total * total);
                else if (total < 0.34)
diff --git a/src/workbook.c b/src/workbook.c
index 25e7a8c83..f90b50536 100644
--- a/src/workbook.c
+++ b/src/workbook.c
@@ -670,11 +670,12 @@ workbook_cells (Workbook *wb, gboolean comments, GnmSheetVisibility vis)
                        continue;
 
                scells = sheet_cell_positions (sheet, comments);
-               g_ptr_array_set_size (cells, oldlen + scells->len);
-               memcpy (&g_ptr_array_index (cells, oldlen),
-                       &g_ptr_array_index (scells, 0),
-                       scells->len * sizeof (GnmEvalPos *));
-
+               if (scells->len) {
+                       g_ptr_array_set_size (cells, oldlen + scells->len);
+                       memcpy (&g_ptr_array_index (cells, oldlen),
+                               &g_ptr_array_index (scells, 0),
+                               scells->len * sizeof (GnmEvalPos *));
+               }
                g_ptr_array_free (scells, TRUE);
        });