[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;
 }