include/fpu/softfloat: implement float16_abs helper

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: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>

include/fpu/softfloat.h

@@ -265,6 +265,13 @@ static inline int float16_is_zero_or_denormal(float16 a)
     return (float16_val(a) & 0x7c00) == 0;
 }
 
+static inline float16 float16_abs(float16 a)
+{
+    /* Note that abs does *not* handle NaN specially, nor does
+     * it flush denormal inputs to zero.
+     */
+    return make_float16(float16_val(a) & 0x7fff);
+}
 /*----------------------------------------------------------------------------
 | The pattern for a default generated half-precision NaN.
 *----------------------------------------------------------------------------*/