Fix for bug #15936: "round" differs on Windows to Unix

Both of our own implementations of rint(3) were inconsistent with the
most common behavior of rint() on those platforms that have it: round
to nearest, break ties by rounding to nearest even.

Fixed by leaving just one implementation of rint() in our source tree,
and changing its behavior to match the most common native
implementations on other platforms.

configure.in:
  Added checks for fenv.h and fesetround().
include/config-win.h:
  Removed the incorrect implementation of rint() for Windows.
include/my_global.h:
  Added an rint() implementation for platforms that do not have it.
mysql-test/r/func_math.result:
  Added a test case for bug #15936.
mysql-test/t/func_math.test:
  Added a test case for bug #15936.
sql/mysqld.cc:
  Explicitly set the FPU rounding mode with fesetround().

1 files changed, 28 insertions, 23 deletions

diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index ca68976d939..7856309b095 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -186,39 +186,44 @@ int initgroups(const char *,unsigned int);
 #ifdef HAVE_FP_EXCEPT				// Fix type conflict
 typedef fp_except fp_except_t;
 #endif
+#endif /* __FreeBSD__ && HAVE_IEEEFP_H */
+#ifdef HAVE_FENV_H
+#include <fenv.h>
+#endif
+#ifdef HAVE_SYS_FPU_H
+/* for IRIX to use set_fpc_csr() */
+#include <sys/fpu.h>
+#endif
 
+inline void setup_fpu()
+{
+#if defined(__FreeBSD__) && defined(HAVE_IEEEFP_H)
   /* We can't handle floating point exceptions with threads, so disable
      this on freebsd
+     Don't fall for overflow, underflow,divide-by-zero or loss of precision
   */
-
-inline void set_proper_floating_point_mode()
-{
-  /* Don't fall for overflow, underflow,divide-by-zero or loss of precision */
 #if defined(__i386__)
   fpsetmask(~(FP_X_INV | FP_X_DNML | FP_X_OFL | FP_X_UFL | FP_X_DZ |
 	      FP_X_IMP));
 #else
- fpsetmask(~(FP_X_INV |             FP_X_OFL | FP_X_UFL | FP_X_DZ |
-	     FP_X_IMP));
-#endif
-}
-#elif defined(__sgi)
-/* for IRIX to use set_fpc_csr() */
-#include <sys/fpu.h>
+  fpsetmask(~(FP_X_INV |             FP_X_OFL | FP_X_UFL | FP_X_DZ |
+              FP_X_IMP));
+#endif /* __i386__ */
+#endif /* __FreeBSD__ && HAVE_IEEEFP_H */
 
-inline void set_proper_floating_point_mode()
-{
+#ifdef HAVE_FESETROUND
+    /* Set FPU rounding mode to "round-to-nearest" */
+  fesetround(FE_TONEAREST);
+#endif /* HAVE_FESETROUND */
+    
+#if defined(__sgi) && defined(HAVE_SYS_FPU_H)
   /* Enable denormalized DOUBLE values support for IRIX */
-  {
-    union fpc_csr n;
-    n.fc_word = get_fpc_csr();
-    n.fc_struct.flush = 0;
-    set_fpc_csr(n.fc_word);
-  }
+  union fpc_csr n;
+  n.fc_word = get_fpc_csr();
+  n.fc_struct.flush = 0;
+  set_fpc_csr(n.fc_word);
+#endif
 }
-#else
-#define set_proper_floating_point_mode()
-#endif /* __FreeBSD__ && HAVE_IEEEFP_H */
 
 } /* cplusplus */
 
@@ -3279,7 +3284,7 @@ static int init_server_components()
   query_cache_init();
   query_cache_resize(query_cache_size);
   randominit(&sql_rand,(ulong) server_start_time,(ulong) server_start_time/2);
-  set_proper_floating_point_mode();
+  setup_fpu();
   init_thr_lock();
 #ifdef HAVE_REPLICATION
   init_slave_list();