[MIPS] ieee754[sd]p_neg workaround

    
It looks glibc's pow() assumes an unary '-' operation for any number
(including NaNs) always inverts its sign bit (though IEEE754 does not
specify the sign bit for NaNs).  This patch make the kernel math-emu
emulates real MIPS neg.[ds] instruction.
    
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 20 insertions, 8 deletions

diff --git a/arch/mips/math-emu/dp_simple.c b/arch/mips/math-emu/dp_simple.c
index 495c1ac94298..1c555e6c6a9f 100644
--- a/arch/mips/math-emu/dp_simple.c
+++ b/arch/mips/math-emu/dp_simple.c
@@ -48,16 +48,22 @@ ieee754dp ieee754dp_neg(ieee754dp x)
 	CLEARCX;
 	FLUSHXDP;
 
+	/*
+	 * Invert the sign ALWAYS to prevent an endless recursion on
+	 * pow() in libc.
+	 */
+	/* quick fix up */
+	DPSIGN(x) ^= 1;
+
 	if (xc == IEEE754_CLASS_SNAN) {
+		ieee754dp y = ieee754dp_indef();
 		SETCX(IEEE754_INVALID_OPERATION);
-		return ieee754dp_nanxcpt(ieee754dp_indef(), "neg");
+		DPSIGN(y) = DPSIGN(x);
+		return ieee754dp_nanxcpt(y, "neg");
 	}
 
 	if (ieee754dp_isnan(x))	/* but not infinity */
 		return ieee754dp_nanxcpt(x, "neg", x);
-
-	/* quick fix up */
-	DPSIGN(x) ^= 1;
 	return x;
 }
 
diff --git a/arch/mips/math-emu/sp_simple.c b/arch/mips/math-emu/sp_simple.c
index c809830dffb4..770f0f4677cd 100644
--- a/arch/mips/math-emu/sp_simple.c
+++ b/arch/mips/math-emu/sp_simple.c
@@ -48,16 +48,22 @@ ieee754sp ieee754sp_neg(ieee754sp x)
 	CLEARCX;
 	FLUSHXSP;
 
+	/*
+	 * Invert the sign ALWAYS to prevent an endless recursion on
+	 * pow() in libc.
+	 */
+	/* quick fix up */
+	SPSIGN(x) ^= 1;
+
 	if (xc == IEEE754_CLASS_SNAN) {
+		ieee754sp y = ieee754sp_indef();
 		SETCX(IEEE754_INVALID_OPERATION);
-		return ieee754sp_nanxcpt(ieee754sp_indef(), "neg");
+		SPSIGN(y) = SPSIGN(x);
+		return ieee754sp_nanxcpt(y, "neg");
 	}
 
 	if (ieee754sp_isnan(x))	/* but not infinity */
 		return ieee754sp_nanxcpt(x, "neg", x);
-
-	/* quick fix up */
-	SPSIGN(x) ^= 1;
 	return x;
 }