MIPS: math-emu: <MAXA|MINA>.<D|S>: Fix cases of input values with opposite signs

Fix the value returned by <MAXA|MINA>.<D|S>, if the inputs are normal
fp numbers of the same absolute value, but opposite signs.

A relevant example:

MAXA.S fd,fs,ft:
  If fs contains -3.0, and ft contains +3.0, fd is going to contain
  +3.0 (without this patch, it used to contain -3.0).

Fixes: a79f5f9ba5 ("MIPS: math-emu: Add support for the MIPS R6 MAX{, A} FPU instruction")
Fixes: 4e9561b20e ("MIPS: math-emu: Add support for the MIPS R6 MIN{, A} FPU instruction")

Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com>
Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: Bo Hu <bohu@google.com>
Cc: Douglas Leung <douglas.leung@imgtec.com>
Cc: Jin Qian <jinqian@google.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Petar Jovanovic <petar.jovanovic@imgtec.com>
Cc: Raghu Gandham <raghu.gandham@imgtec.com>
Cc: <stable@vger.kernel.org> # 4.3+
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16883/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/dp_fmax.c

@@ -243,7 +243,11 @@ union ieee754dp ieee754dp_fmaxa(union ieee754dp x, union ieee754dp y)
 		return y;
 
 	/* Compare mantissa */
-	if (xm <= ym)
+	if (xm < ym)
 		return y;
-	return x;
+	else if (xm > ym)
+		return x;
+	else if (xs == 0)
+		return x;
+	return y;
 }

arch/mips/math-emu/dp_fmin.c

@@ -243,7 +243,11 @@ union ieee754dp ieee754dp_fmina(union ieee754dp x, union ieee754dp y)
 		return x;
 
 	/* Compare mantissa */
-	if (xm <= ym)
+	if (xm < ym)
+		return x;
+	else if (xm > ym)
+		return y;
+	else if (xs == 1)
 		return x;
 	return y;
 }

arch/mips/math-emu/sp_fmax.c

@@ -243,7 +243,11 @@ union ieee754sp ieee754sp_fmaxa(union ieee754sp x, union ieee754sp y)
 		return y;
 
 	/* Compare mantissa */
-	if (xm <= ym)
+	if (xm < ym)
 		return y;
-	return x;
+	else if (xm > ym)
+		return x;
+	else if (xs == 0)
+		return x;
+	return y;
 }

arch/mips/math-emu/sp_fmin.c

@@ -243,7 +243,11 @@ union ieee754sp ieee754sp_fmina(union ieee754sp x, union ieee754sp y)
 		return x;
 
 	/* Compare mantissa */
-	if (xm <= ym)
+	if (xm < ym)
+		return x;
+	else if (xm > ym)
+		return y;
+	else if (xs == 1)
 		return x;
 	return y;
 }