diff -Naur mpfr-2.1.0-p16/ui_sub.c mpfr-2.1.0-p17/ui_sub.c
--- mpfr-2.1.0-p16/ui_sub.c	2004-04-07 14:42:32.000000000 +0000
+++ mpfr-2.1.0-p17/ui_sub.c	2005-02-21 13:17:42.639432000 +0000
@@ -1,6 +1,6 @@
 /* mpfr_ui_sub -- subtract a floating-point number from an integer
 
-Copyright 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
+Copyright 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
 
 This file is part of the MPFR Library.
 
@@ -28,7 +28,10 @@
   mpfr_t uu;
   mp_limb_t up[1];
   unsigned long cnt;
-  
+
+  if (MPFR_UNLIKELY (u == 0))
+    return mpfr_neg (y, x, rnd_mode);
+
   if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(x)))
     {
       if (MPFR_IS_NAN(x))
@@ -47,7 +50,7 @@
 	/* u - 0 = u */
 	return mpfr_set_ui(y, u, rnd_mode);
     }
-  else if (MPFR_LIKELY(u))
+  else
     {
       MPFR_TMP_INIT1 (up, uu, BITS_PER_MP_LIMB);
       MPFR_ASSERTN(u == (mp_limb_t) u);
@@ -56,7 +59,4 @@
       MPFR_SET_EXP (uu, BITS_PER_MP_LIMB - cnt);
       return mpfr_sub (y, uu, x, rnd_mode);
     }
-  else
-    /* u == 0 BUT x != 0 */
-    return mpfr_neg (y, x, rnd_mode); /* if u=0, then set y to -x */
 }