[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>

diff --git a/arch/mips/math-emu/dp_simple.c b/arch/mips/math-emu/dp_simple.c
index 495c1ac..1c555e6 100644 (file)
--- 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 c809830..770f0f4 100644 (file)
--- 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;
 }