MIPS: math-emu: Update sNaN quieting handlers

Commit fdffbafb [Lots of FPU bug fixes from Kjeld Borch Egevang.]
replaced the two single `ieee754sp_nanxcpt' and `ieee754dp_nanxcpt'
places, where sNaN quieting used to happen for single and double
floating-point operations respectively, with individual qNaN
instantiations across all the call sites instead.  It also made most of
these two functions dead code as where called on a qNaN they return
right away.

To revert the damage and make sNaN quieting uniform again first rewrite
`ieee754sp_nanxcpt' and `ieee754dp_nanxcpt' to do the same quieting all
the call sites do, that is return the default qNaN encoding for all
input sNaN values; never propagate any sNaN payload bits from its
trailing significand field.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9685/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/ieee754dp.c

@@ -49,14 +49,9 @@ union ieee754dp __cold ieee754dp_nanxcpt(union ieee754dp r)
 	if (!ieee754dp_issnan(r))	/* QNAN does not cause invalid op !! */
 		return r;
 
-	if (!ieee754_setandtestcx(IEEE754_INVALID_OPERATION)) {
-		/* not enabled convert to a quiet NaN */
-		DPMANT(r) &= (~DP_MBIT(DP_FBITS-1));
-		if (ieee754dp_isnan(r))
-			return r;
-		else
-			return ieee754dp_indef();
-	}
+	/* If not enabled convert to a quiet NaN.  */
+	if (!ieee754_setandtestcx(IEEE754_INVALID_OPERATION))
+		return ieee754dp_indef();
 
 	return r;
 }

arch/mips/math-emu/ieee754sp.c

@@ -49,14 +49,9 @@ union ieee754sp __cold ieee754sp_nanxcpt(union ieee754sp r)
 	if (!ieee754sp_issnan(r))	/* QNAN does not cause invalid op !! */
 		return r;
 
-	if (!ieee754_setandtestcx(IEEE754_INVALID_OPERATION)) {
-		/* not enabled convert to a quiet NaN */
-		SPMANT(r) &= (~SP_MBIT(SP_FBITS-1));
-		if (ieee754sp_isnan(r))
-			return r;
-		else
-			return ieee754sp_indef();
-	}
+	/* If not enabled convert to a quiet NaN.  */
+	if (!ieee754_setandtestcx(IEEE754_INVALID_OPERATION))
+		return ieee754sp_indef();
 
 	return r;
 }