FPU: Fix setting of r.x for single-precision operations

The fp_rounding function expects r.x to have been set based on the lower
31 bits of r.r, not 29 as presently done, so change 28 to SP_RBIT-1
(SP_RBIT is 31).  Also add a test to check.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

fpu.vhdl

@@ -3239,7 +3239,7 @@ begin
 
         -- If shifting right, test if bits of R will be shifted out of significance
         if r.longmask = '1' then
-            mshift := to_signed(28, EXP_BITS);
+            mshift := to_signed(SP_RBIT - 1, EXP_BITS);
         else
             mshift := to_signed(-1, EXP_BITS);
         end if;

tests/fpu/fpu.c

@@ -680,6 +680,7 @@ struct roundvals {
 	{ FPS_RN_NEAR,			0x38012345b0000000, 0x38012345c0000000, FPS_FR|FPS_FI },
 	{ FPS_RN_NEAR,			0x37c12345b0000000, 0x37c1234400000000, FPS_FI },
 	{ FPS_RN_NEAR,			0x0000008800000088, 0,			FPS_FI },
+	{ FPS_RN_NEAR,			0xc2000000c2000000, 0xc2000000c0000000,	FPS_FI },
 };
 
 int test8(long arg)