softfloat: add _set_sign(), _infinity and _half for 32 and 64 bits floats.

These constants and utility function are needed to implement some
helpers. Defining constants avoids the need to re-compute them at
runtime.

Signed-off-by: Christophe Lyon <christophe.lyon@st.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

fpu/softfloat.h

diff --git a/fpu/softfloat.h b/fpu/softfloat.h
index f34a938..fd61dc4 100644
--- a/fpu/softfloat.h
+++ b/fpu/softfloat.h
@@ -379,9 +379,16 @@
     return (float32_val(a) & 0x7f800000) == 0;
 }
 
+INLINE float32 float32_set_sign(float32 a, int sign)
+{
+    return make_float32((float32_val(a) & 0x7fffffff) | (sign << 31));
+}
+
 #define float32_zero make_float32(0)
 #define float32_one make_float32(0x3f800000)
 #define float32_ln2 make_float32(0x3f317218)
+#define float32_half make_float32(0x3f000000)
+#define float32_infinity make_float32(0x7f800000)
 
 
 /*----------------------------------------------------------------------------
@@ -479,9 +486,17 @@
     return ((float64_val(a) & ~(1ULL << 63)) > 0x7ff0000000000000ULL);
 }
 
+INLINE float64 float64_set_sign(float64 a, int sign)
+{
+    return make_float64((float64_val(a) & 0x7fffffffffffffffULL)
+                        | ((int64_t)sign << 63));
+}
+
 #define float64_zero make_float64(0)
 #define float64_one make_float64(0x3ff0000000000000LL)
 #define float64_ln2 make_float64(0x3fe62e42fefa39efLL)
+#define float64_half make_float64(0x3fe0000000000000LL)
+#define float64_infinity make_float64(0x7ff0000000000000LL)
 
 /*----------------------------------------------------------------------------
 | The pattern for a default generated double-precision NaN.