[gnumeric] FPU: Add sanity check for floating-point environment.

[Morten Welinder <mortenw src gnome org>]

commit 76168c69c491c77c83c1e3a923225077fb2a027b
Author: Morten Welinder <terra gnome org>
Date:   Fri Mar 23 11:12:38 2018 -0400

    FPU: Add sanity check for floating-point environment.
    
    Windows run Linux binaries in "double", not "extended", mode.

 ChangeLog              |    4 ++++
 NEWS                   |    3 +++
 configure.ac           |    3 +++
 src/main-application.c |   27 +++++++++++++++++++++++++++
 4 files changed, 37 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 593984d..069e8b2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2018-03-23  Morten Welinder  <terra gnome org>
+
+       * src/main-application.c (cpu_sanity_check): New function.
+
 2018-03-13  Morten Welinder <terra gnome org>
 
        * configure.ac: Post-release bump.
diff --git a/NEWS b/NEWS
index 97207ba..b63cb6b 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,8 @@
 Gnumeric 1.12.40
 
+Morten:
+       * Add floating-point environment sanity check.  [#794515]
+
 --------------------------------------------------------------------------
 Gnumeric 1.12.39
 
diff --git a/configure.ac b/configure.ac
index 007580d..4e3b9b8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -543,6 +543,9 @@ AC_CHECK_HEADERS(langinfo.h)
 dnl check for rlimit
 AC_CHECK_HEADERS(sys/resource.h)
 
+dnl we need to check fpu mode
+AC_CHECK_HEADERS(fpu_control.h)
+
 SAVE_CFLAGS=$CFLAGS
 SAVE_LIBS=$LIBS
 CFLAGS="$CFLAGS $GNUMERIC_CFLAGS"
diff --git a/src/main-application.c b/src/main-application.c
index 60eb357..a42b6e7 100644
--- a/src/main-application.c
+++ b/src/main-application.c
@@ -46,6 +46,10 @@
 #include <string.h>
 #include <locale.h>
 
+#ifdef HAVE_FPU_CONTROL_H
+#include <fpu_control.h>
+#endif
+
 static gboolean immediate_exit_flag = FALSE;
 static gboolean gnumeric_no_splash = FALSE;
 static gboolean gnumeric_no_warnings = FALSE;
@@ -161,6 +165,27 @@ cb_workbook_removed (void)
        }
 }
 
+static void
+cpu_sanity_check (void)
+{
+#if (defined(i386) || defined(__i386__) || defined(__i386) || defined(__x86_64__) || defined(__x86_64)) && 
HAVE_FPU_CONTROL_H
+       fpu_control_t state;
+       const fpu_control_t mask = _FPU_EXTENDED | _FPU_DOUBLE | _FPU_SINGLE;
+
+       _FPU_GETCW (state);
+       if ((state & mask) != _FPU_EXTENDED) {
+               // Evidently currentlly happinging when Windows runs Linux
+               // binaries.  See bug 794515.
+               g_warning ("Sanity check failed!  The cpu is not in \"extended\" mode as it should be.  
Attempting to fix, but expect trouble.");
+               state = (state & ~mask) | _FPU_EXTENDED;
+               _FPU_SETCW (state);
+       }
+#else
+       // Hope for the best
+#endif
+}
+
+
 int
 main (int argc, char const **argv)
 {
@@ -177,6 +202,8 @@ main (int argc, char const **argv)
        /* No code before here, we need to init threads */
        argv = gnm_pre_parse_init (argc, argv);
 
+       cpu_sanity_check ();
+
        /*
         * Attempt to disable Ubuntu's funky, non-working scroll
         * bars.  This needs to be done before gtk starts loading