darwin-ldouble.c: Add big comment explaining exactly what is expected as a 'long double'.

	* config/rs6000/darwin-ldouble.c: Add big comment explaining
	exactly what is expected as a 'long double'.
	(_xlqadd): When a value to be returned is representable as a
	'double', just return it directly, do not construct it using a union.
	Also, correct final fixup.
	(_xlqmul): Likewise.
	(_xlqdiv): Likewise.
	* real.c (encode_ibm_extended): Make consistent with darwin-ldouble.c.

From-SVN: r75629

1 files changed, 15 insertions, 45 deletions

diff --git a/gcc/real.c b/gcc/real.c
index f7af346..ecee90b 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -3235,53 +3235,23 @@ encode_ibm_extended (const struct real_format *fmt, long *buf,
 
   base_fmt = fmt->qnan_msb_set ? &ieee_double_format : &mips_double_format;
 
-  switch (r->class)
-    {
-    case rvc_zero:
-      /* Both doubles have sign bit set.  */
-      buf[0] = FLOAT_WORDS_BIG_ENDIAN ? r->sign << 31 : 0;
-      buf[1] = FLOAT_WORDS_BIG_ENDIAN ? 0 : r->sign << 31;
-      buf[2] = buf[0];
-      buf[3] = buf[1];
-      break;
-
-    case rvc_inf:
-    case rvc_nan:
-      /* Both doubles set to Inf / NaN.  */
-      encode_ieee_double (base_fmt, &buf[0], r);
-      buf[2] = buf[0];
-      buf[3] = buf[1];
-      return;
+  /* u = IEEE double precision portion of significand.  */
+  u = *r;
+  round_for_format (base_fmt, &u);
+  encode_ieee_double (base_fmt, &buf[0], &u);
 
-    case rvc_normal:
-      /* u = IEEE double precision portion of significand.  */
-      u = *r;
-      clear_significand_below (&u, SIGNIFICAND_BITS - 53);
-
-      normalize (&u);
-      /* If the upper double is zero, we have a denormal double, so
-	 move it to the first double and leave the second as zero.  */
-      if (u.class == rvc_zero)
-	{
-	  v = u;
-	  u = *r;
-	  normalize (&u);
-	}
-      else
-	{
-	  /* v = remainder containing additional 53 bits of significand.  */
-	  do_add (&v, r, &u, 1);
-	  round_for_format (base_fmt, &v);
-	}
-
-      round_for_format (base_fmt, &u);
-
-      encode_ieee_double (base_fmt, &buf[0], &u);
+  if (r->class == rvc_normal)
+    {
+      do_add (&v, r, &u, 1);
+      round_for_format (base_fmt, &v);
       encode_ieee_double (base_fmt, &buf[2], &v);
-      break;
-
-    default:
-      abort ();
+    }
+  else
+    {
+      /* Inf, NaN, 0 are all representable as doubles, so the
+	 least-significant part can be 0.0.  */
+      buf[2] = 0;
+      buf[3] = 0;
     }
 }