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Re: [wide-int] Various division fixes


On 10/31/2013 05:01 AM, Richard Sandiford wrote:
There are several Ada failures on the branch, all related to division
and modulus:

- div_floor adjusted truncated negative quotients in the wrong direction
   (up instead of down).  E.g. -5 /[fl] 2 gave -1 rather than -3.

- {div,mod}_round used the wrong condition to check when rounding was needed.

- The routines checked for negative results by testing the sign of the
   (truncated) quotient directly.  That doesn't work when the true
   quotient is in the range (-1, 0) and gets truncated to zero.

Tested on x86_64-linux-gnu and powerpc64-linux-gnu.  OK to install?

Thanks,
Richard
yes, these look fine.   kenny

Index: gcc/wide-int.h
===================================================================
--- gcc/wide-int.h	2013-10-31 08:46:18.081178550 +0000
+++ gcc/wide-int.h	2013-10-31 08:53:50.741900740 +0000
@@ -2250,8 +2250,8 @@ wi::div_floor (const T1 &x, const T2 &y,
  				     yi.val, yi.len, yi.precision, sgn,
  				     overflow));
    remainder.set_len (remainder_len);
-  if (wi::neg_p (quotient, sgn) && remainder != 0)
-    return quotient + 1;
+  if (wi::neg_p (x, sgn) != wi::neg_p (y, sgn) && remainder != 0)
+    return quotient - 1;
    return quotient;
  }
@@ -2292,7 +2292,7 @@ wi::div_ceil (const T1 &x, const T2 &y,
  				     yi.val, yi.len, yi.precision, sgn,
  				     overflow));
    remainder.set_len (remainder_len);
-  if (!wi::neg_p (quotient, sgn) && remainder != 0)
+  if (wi::neg_p (x, sgn) == wi::neg_p (y, sgn) && remainder != 0)
      return quotient + 1;
    return quotient;
  }
@@ -2322,10 +2322,10 @@ wi::div_round (const T1 &x, const T2 &y,
      {
        if (sgn == SIGNED)
  	{
-	  if (wi::gts_p (wi::lrshift (wi::abs (y), 1),
-			 wi::abs (remainder)))
+	  if (wi::ges_p (wi::abs (remainder),
+			 wi::lrshift (wi::abs (y), 1)))
  	    {
-	      if (wi::neg_p (quotient))
+	      if (wi::neg_p (x, sgn) != wi::neg_p (y, sgn))
  		return quotient - 1;
  	      else
  		return quotient + 1;
@@ -2333,16 +2333,15 @@ wi::div_round (const T1 &x, const T2 &y,
  	}
        else
  	{
-	  if (wi::gtu_p (wi::lrshift (y, 1), remainder))
+	  if (wi::geu_p (remainder, wi::lrshift (y, 1)))
  	    return quotient + 1;
  	}
      }
    return quotient;
  }
-/* Return X / Y, rouding towards nearest with ties away from zero.
-   Treat X and Y as having the signedness given by SGN.  Store the
-   remainder in *REMAINDER_PTR.  */
+/* Return X / Y, rouding towards 0.  Treat X and Y as having the
+   signedness given by SGN.  Store the remainder in *REMAINDER_PTR.  */
  template <typename T1, typename T2>
  inline WI_BINARY_RESULT (T1, T2)
  wi::divmod_trunc (const T1 &x, const T2 &y, signop sgn,
@@ -2425,7 +2424,7 @@ wi::mod_floor (const T1 &x, const T2 &y,
  				     overflow));
    remainder.set_len (remainder_len);
- if (wi::neg_p (quotient, sgn) && remainder != 0)
+  if (wi::neg_p (x, sgn) != wi::neg_p (y, sgn) && remainder != 0)
      return remainder + y;
    return remainder;
  }
@@ -2461,7 +2460,7 @@ wi::mod_ceil (const T1 &x, const T2 &y,
  				     overflow));
    remainder.set_len (remainder_len);
- if (!wi::neg_p (quotient, sgn) && remainder != 0)
+  if (wi::neg_p (x, sgn) == wi::neg_p (y, sgn) && remainder != 0)
      return remainder - y;
    return remainder;
  }
@@ -2491,10 +2490,10 @@ wi::mod_round (const T1 &x, const T2 &y,
      {
        if (sgn == SIGNED)
  	{
-	  if (wi::gts_p (wi::lrshift (wi::abs (y), 1),
-			 wi::abs (remainder)))
+	  if (wi::ges_p (wi::abs (remainder),
+			 wi::lrshift (wi::abs (y), 1)))
  	    {
-	      if (wi::neg_p (quotient))
+	      if (wi::neg_p (x, sgn) != wi::neg_p (y, sgn))
  		return remainder + y;
  	      else
  		return remainder - y;
@@ -2502,7 +2501,7 @@ wi::mod_round (const T1 &x, const T2 &y,
  	}
        else
  	{
-	  if (wi::gtu_p (wi::lrshift (y, 1), remainder))
+	  if (wi::geu_p (remainder, wi::lrshift (y, 1)))
  	    return remainder - y;
  	}
      }


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