diff -Naurd mpfr-3.1.2-a/PATCHES mpfr-3.1.2-b/PATCHES
--- mpfr-3.1.2-a/PATCHES	2013-10-09 13:34:21.000000000 +0000
+++ mpfr-3.1.2-b/PATCHES	2013-10-09 13:34:21.000000000 +0000
@@ -0,0 +1 @@
+clang-divby0
diff -Naurd mpfr-3.1.2-a/VERSION mpfr-3.1.2-b/VERSION
--- mpfr-3.1.2-a/VERSION	2013-09-26 10:52:52.000000000 +0000
+++ mpfr-3.1.2-b/VERSION	2013-10-09 13:34:21.000000000 +0000
@@ -1 +1 @@
-3.1.2-p2
+3.1.2-p3
diff -Naurd mpfr-3.1.2-a/src/mpfr-impl.h mpfr-3.1.2-b/src/mpfr-impl.h
--- mpfr-3.1.2-a/src/mpfr-impl.h	2013-03-13 15:37:36.000000000 +0000
+++ mpfr-3.1.2-b/src/mpfr-impl.h	2013-10-09 13:34:21.000000000 +0000
@@ -468,8 +468,16 @@
 #define MPFR_LIMBS_PER_FLT ((IEEE_FLT_MANT_DIG-1)/GMP_NUMB_BITS+1)
 
 /* Visual C++ doesn't support +1.0/0.0, -1.0/0.0 and 0.0/0.0
-   at compile time. */
-#if defined(_MSC_VER) && defined(_WIN32) && (_MSC_VER >= 1200)
+   at compile time.
+   Clang with -fsanitize=undefined is a bit similar due to a bug:
+     http://llvm.org/bugs/show_bug.cgi?id=17381
+   but even without its sanitizer, it may be better to use the
+   double_zero version until IEEE 754 division by zero is properly
+   supported:
+     http://llvm.org/bugs/show_bug.cgi?id=17000
+*/
+#if (defined(_MSC_VER) && defined(_WIN32) && (_MSC_VER >= 1200)) || \
+    defined(__clang__)
 static double double_zero = 0.0;
 # define DBL_NAN (double_zero/double_zero)
 # define DBL_POS_INF ((double) 1.0/double_zero)
@@ -501,6 +509,8 @@
    (with Xcode 2.4.1, i.e. the latest one). */
 #define LVALUE(x) (&(x) == &(x) || &(x) != &(x))
 #define DOUBLE_ISINF(x) (LVALUE(x) && ((x) > DBL_MAX || (x) < -DBL_MAX))
+/* The DOUBLE_ISNAN(x) macro is also valid on long double x
+   (assuming that the compiler isn't too broken). */
 #ifdef MPFR_NANISNAN
 /* Avoid MIPSpro / IRIX64 / gcc -ffast-math (incorrect) optimizations.
    The + must not be replaced by a ||. With gcc -ffast-math, NaN is
diff -Naurd mpfr-3.1.2-a/src/mpfr.h mpfr-3.1.2-b/src/mpfr.h
--- mpfr-3.1.2-a/src/mpfr.h	2013-09-26 10:52:52.000000000 +0000
+++ mpfr-3.1.2-b/src/mpfr.h	2013-10-09 13:34:21.000000000 +0000
@@ -27,7 +27,7 @@
 #define MPFR_VERSION_MAJOR 3
 #define MPFR_VERSION_MINOR 1
 #define MPFR_VERSION_PATCHLEVEL 2
-#define MPFR_VERSION_STRING "3.1.2-p2"
+#define MPFR_VERSION_STRING "3.1.2-p3"
 
 /* Macros dealing with MPFR VERSION */
 #define MPFR_VERSION_NUM(a,b,c) (((a) << 16L) | ((b) << 8) | (c))
diff -Naurd mpfr-3.1.2-a/src/version.c mpfr-3.1.2-b/src/version.c
--- mpfr-3.1.2-a/src/version.c	2013-09-26 10:52:52.000000000 +0000
+++ mpfr-3.1.2-b/src/version.c	2013-10-09 13:34:21.000000000 +0000
@@ -25,5 +25,5 @@
 const char *
 mpfr_get_version (void)
 {
-  return "3.1.2-p2";
+  return "3.1.2-p3";
 }
diff -Naurd mpfr-3.1.2-a/tests/tget_flt.c mpfr-3.1.2-b/tests/tget_flt.c
--- mpfr-3.1.2-a/tests/tget_flt.c	2013-03-13 15:37:44.000000000 +0000
+++ mpfr-3.1.2-b/tests/tget_flt.c	2013-10-09 13:34:21.000000000 +0000
@@ -28,9 +28,17 @@
 main (void)
 {
   mpfr_t x, y;
-  float f, g, infp;
+  float f, g;
   int i;
+#if !defined(MPFR_ERRDIVZERO)
+  float infp;
+#endif
+
+  tests_start_mpfr ();
 
+#if !defined(MPFR_ERRDIVZERO)
+  /* The definition of DBL_POS_INF involves a division by 0. This makes
+     "clang -O2 -fsanitize=undefined -fno-sanitize-recover" fail. */
   infp = (float) DBL_POS_INF;
   if (infp * 0.5 != infp)
     {
@@ -38,8 +46,7 @@
       fprintf (stderr, "(this is probably a compiler bug, please report)\n");
       exit (1);
     }
-
-  tests_start_mpfr ();
+#endif
 
   mpfr_init2 (x, 24);
   mpfr_init2 (y, 24);
@@ -353,6 +360,7 @@
       printf ("expected %.8e, got %.8e\n", g, f);
       exit (1);
     }
+#if !defined(MPFR_ERRDIVZERO)
   f = mpfr_get_flt (x, MPFR_RNDN); /* first round to 2^128 (even rule),
                                       thus we should get +Inf */
   g = infp;
@@ -376,6 +384,7 @@
       printf ("expected %.8e, got %.8e\n", g, f);
       exit (1);
     }
+#endif
 
   mpfr_clear (x);
   mpfr_clear (y);
diff -Naurd mpfr-3.1.2-a/tests/tset_ld.c mpfr-3.1.2-b/tests/tset_ld.c
--- mpfr-3.1.2-a/tests/tset_ld.c	2013-03-13 15:37:44.000000000 +0000
+++ mpfr-3.1.2-b/tests/tset_ld.c	2013-10-09 13:34:21.000000000 +0000
@@ -47,8 +47,11 @@
 static int
 Isnan_ld (long double d)
 {
-  double e = (double) d;
-  if (DOUBLE_ISNAN (e))
+  /* Do not convert d to double as this can give an overflow, which
+     may confuse compilers without IEEE 754 support (such as clang
+     -fsanitize=undefined), or trigger a trap if enabled.
+     The DOUBLE_ISNAN macro should work fine on long double. */
+  if (DOUBLE_ISNAN (d))
     return 1;
   LONGDOUBLE_NAN_ACTION (d, goto yes);
   return 0;