[PATCH] fix branch emulation for floating-point exceptions

[Win Treese <treese@acm.org>]

In the branch emulation for floating-point exceptions,  
__compute_return_epc
must determine for bc1f et al which condition code bit to test. This  
is based on bits <4:2>
of the rt field. The switch statement to distinguish bc1f et al needs  
to use only the
two low bits of rt, but the old code tests on the whole rt field.  
This patch masks off
the proper bits.

Signed-off-by: Win Treese <treese@acm.org>

Index: a/arch/mips/kernel/branch.c
===================================================================
--- a/arch/mips/kernel/branch.c (revision 18809)
+++ a/arch/mips/kernel/branch.c (working copy)
@@ -184,7 +184,7 @@
                bit = (insn.i_format.rt >> 2);
                bit += (bit != 0);
                bit += 23;
-               switch (insn.i_format.rt) {
+               switch (insn.i_format.rt & 3) {
                case 0: /* bc1f */
                case 2: /* bc1fl */
                        if (~fcr31 & (1 << bit))