cmp2.c: Integer overflows checked.

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1479 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 39 insertions, 17 deletions

diff --git a/cmp2.c b/cmp2.c
index 736194431..e7451bdeb 100644
--- a/cmp2.c
+++ b/cmp2.c
@@ -19,7 +19,6 @@ along with the MPFR Library; see the file COPYING.LIB.  If not, write to
 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 MA 02111-1307, USA. */
 
-#include <stdio.h>
 #include "gmp.h"
 #include "gmp-impl.h"
 #include "longlong.h"
@@ -27,8 +26,8 @@ MA 02111-1307, USA. */
 #include "mpfr-impl.h"
 
 /* returns the number of cancelled bits when one subtracts abs(c) from abs(b). 
-   Assumes b>=c, which implies MPFR_EXP(b)>=MPFR_EXP(c).
-   if b=c, returns prec(b).
+   Assumes |b| >= |c|, which implies MPFR_EXP(b)>=MPFR_EXP(c).
+   if |b| = |c|, returns prec(b).
 
    Assumes neither of b or c is NaN or +/- infinity.
 
@@ -38,10 +37,17 @@ mp_prec_t
 mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 {
   mp_limb_t *bp, *cp, bb, cc = 0, lastc = 0, dif, high_dif = 0;
-  long bn, cn, z;
-  unsigned long diff_exp, res = 0;
+  mp_size_t bn, cn;
+  mp_exp_unsigned_t diff_exp;
+  mp_prec_t res = 0;
 
-  if (MPFR_IS_ZERO(c)) return 0;
+  MPFR_ASSERTN(MPFR_IS_FP(b));
+  MPFR_ASSERTN(MPFR_IS_FP(c));
+
+  if (MPFR_IS_ZERO(c))
+    return 0;
+
+  MPFR_ASSERTN(MPFR_NOTZERO(b));
 
   bp = MPFR_MANT(b);
   cp = MPFR_MANT(c);
@@ -49,7 +55,8 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
   bn = (MPFR_PREC(b) - 1) / BITS_PER_MP_LIMB;
   cn = (MPFR_PREC(c) - 1) / BITS_PER_MP_LIMB;
 
-  diff_exp = MPFR_EXP(b) - MPFR_EXP(c);
+  MPFR_ASSERTN(MPFR_EXP(b) >= MPFR_EXP(c));
+  diff_exp = (mp_exp_unsigned_t) MPFR_EXP(b) - MPFR_EXP(c);
   
   if (diff_exp == 0) /* otherwise the shifted most significant limb of c
 			cannot match bp[bn] */
@@ -66,6 +73,8 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 
       if (cn < 0) /* c discards exactly the upper part of b */
 	{
+          unsigned int z;
+
 	  while (bn>=0 && bp[bn]==0)
 	    {
 	      bn--;
@@ -82,11 +91,13 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 
   /* now we have removed the identical upper limbs of b and c
      (can happen only when diff_exp = 0): bp[bn] > cc, bn>=0, cn>=0 */
+
   if (diff_exp < BITS_PER_MP_LIMB)
     {
       cc = cp[cn] >> diff_exp;
       /* warning: a shift by BITS_PER_MP_LIMB may give wrong results */
-      if (diff_exp) lastc = cp[cn] << (BITS_PER_MP_LIMB - diff_exp);
+      if (diff_exp)
+        lastc = cp[cn] << (BITS_PER_MP_LIMB - diff_exp);
       cn--;
     }
   else
@@ -94,14 +105,21 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 
   dif = bp[bn--] - cc; /* necessarily dif >= 1 */
 
-  while ((cn>=0 || lastc) && (high_dif==0) && (dif==1))
+  while ((cn >= 0 || lastc != 0) && (high_dif == 0) && (dif == 1))
     { /* dif=1 implies diff_exp = 0 or 1 */
       bb = (bn >= 0) ? bp[bn] : 0;
       cc = lastc;
       if (cn >= 0)
 	{
-	  cc += cp[cn] >> diff_exp;
-	  if (diff_exp) lastc = cp[cn] << (BITS_PER_MP_LIMB - diff_exp);
+          if (diff_exp == 0)
+            {
+              cc += cp[cn];
+            }
+          else /* diff_exp = 1 */
+            {
+              cc += cp[cn] >> 1;
+              lastc = cp[cn] << (BITS_PER_MP_LIMB - 1);
+            }
 	}
       else
 	lastc = 0;
@@ -113,14 +131,16 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 
   /* (cn<0 and lastc=0) or (high_dif,dif)<>(0,1) */
 
-  if (high_dif) /* necessarily high_dif = 1 */
+  if (high_dif != 0) /* necessarily high_dif = 1 */
     {
       res--;
-      if (dif)
+      if (dif != 0)
 	return res;
     }
   else /* high_dif = 0 */
     {
+      unsigned int z;
+
       count_leading_zeros(z, dif); /* dif > 1 here */
       res += z;
       if (dif != ((mp_limb_t) 1 << (BITS_PER_MP_LIMB - z - 1)))
@@ -128,7 +148,7 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
     }
 
   /* now result is res + (low(b) < low(c)) */
-  while (bn>=0 && (cn>=0 || lastc))
+  while (bn >= 0 && (cn >= 0 || lastc != 0))
     {
       if (diff_exp >= BITS_PER_MP_LIMB)
 	diff_exp -= BITS_PER_MP_LIMB;
@@ -138,7 +158,8 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 	  if (cn >= 0)
 	    {
 	      cc += cp[cn] >> diff_exp;
-	      if (diff_exp) lastc = cp[cn] << (BITS_PER_MP_LIMB - diff_exp);
+	      if (diff_exp != 0)
+                lastc = cp[cn] << (BITS_PER_MP_LIMB - diff_exp);
 	    }
 	  else
 	    lastc = 0;
@@ -151,9 +172,10 @@ mpfr_cmp2 (mpfr_srcptr b, mpfr_srcptr c)
 
   if (bn < 0)
     {
-      if (lastc)
+      if (lastc != 0)
 	return res + 1;
-      while (cn>=0 && cp[cn]==0) cn--;
+      while (cn >= 0 && cp[cn] == 0)
+        cn--;
       return res + (cn >= 0);
     }