Prefer to use gmtime_s instead

MinGW-w64 defines _gmtime64_s on both i686 and x86_64 targets.
Prefer to use the gmtime_s macro to avoid that _gmtime64_s is
being called on Windows 32-bit, which will not work.

This commit also generally ensures that a threadsafe alternative
is provided for toolchains targeting Windows i686.

1 files changed, 15 insertions, 2 deletions

diff --git a/configure.ac b/configure.ac
index e3aae27..32b3979 100644
--- a/configure.ac
+++ b/configure.ac
@@ -81,8 +81,21 @@ AX_APPEND_COMPILE_FLAGS(["-fvisibility=hidden"])
 # Motorola and SPARC CPUs), define `WORDS_BIGENDIAN'.
 AC_C_BIGENDIAN
 
-# Check for functions that some compilers lack (or name differently)
-AC_CHECK_FUNCS([gmtime_r _gmtime64_s])
+# Check for threadsafe variants of gmtime
+# Note: check for gmtime_s is a bit more complex as it is implemented as a macro
+AC_CHECK_FUNCS(gmtime_r, [], [
+               AC_MSG_CHECKING([for gmtime_s])
+               AC_LINK_IFELSE([
+                 AC_LANG_PROGRAM([[#include <time.h>]], [[
+                   time_t t;
+                   struct tm m;
+                   gmtime_s(&m, &t);
+                   return 0;
+                 ]])],
+                 [AC_MSG_RESULT([yes])
+                  AC_DEFINE([HAVE_GMTIME_S], [1], [gmtime_s can be used])], 
+                 [AC_MSG_RESULT([no])]
+               )])
 
 # Point to JPEG installed in DIR or disable JPEG with --without-jpeg.
 AC_ARG_WITH(jpeg,