fpu/softfloat: implement float16_squash_input_denormal

This will be required when expanding the MINMAX() macro for 16
bit/half-precision operations.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>

fpu/softfloat.c

@@ -3488,6 +3488,21 @@ static float16 roundAndPackFloat16(flag zSign, int zExp,
     return packFloat16(zSign, zExp, zSig >> 13);
 }
 
+/*----------------------------------------------------------------------------
+| If `a' is denormal and we are in flush-to-zero mode then set the
+| input-denormal exception and return zero. Otherwise just return the value.
+*----------------------------------------------------------------------------*/
+float16 float16_squash_input_denormal(float16 a, float_status *status)
+{
+    if (status->flush_inputs_to_zero) {
+        if (extractFloat16Exp(a) == 0 && extractFloat16Frac(a) != 0) {
+            float_raise(float_flag_input_denormal, status);
+            return make_float16(float16_val(a) & 0x8000);
+        }
+    }
+    return a;
+}
+
 static void normalizeFloat16Subnormal(uint32_t aSig, int *zExpPtr,
                                       uint32_t *zSigPtr)
 {

include/fpu/softfloat.h

@@ -277,6 +277,7 @@ void float_raise(uint8_t flags, float_status *status);
 | If `a' is denormal and we are in flush-to-zero mode then set the
 | input-denormal exception and return zero. Otherwise just return the value.
 *----------------------------------------------------------------------------*/
+float16 float16_squash_input_denormal(float16 a, float_status *status);
 float32 float32_squash_input_denormal(float32 a, float_status *status);
 float64 float64_squash_input_denormal(float64 a, float_status *status);