drm/amd/display: add fixed point fractional bit truncation function

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/include/fixed31_32.h

@@ -496,4 +496,21 @@ unsigned int dc_fixpt_clamp_u0d10(struct fixed31_32 arg);
 
 int dc_fixpt_s4d19(struct fixed31_32 arg);
 
+static inline struct fixed31_32 dc_fixpt_truncate(struct fixed31_32 arg, unsigned int frac_bits)
+{
+	bool negative = arg.value < 0;
+
+	if (frac_bits >= FIXED31_32_BITS_PER_FRACTIONAL_PART) {
+		ASSERT(frac_bits == FIXED31_32_BITS_PER_FRACTIONAL_PART);
+		return arg;
+	}
+
+	if (negative)
+		arg.value = -arg.value;
+	arg.value &= (~0LL) << (FIXED31_32_BITS_PER_FRACTIONAL_PART - frac_bits);
+	if (negative)
+		arg.value = -arg.value;
+	return arg;
+}
+
 #endif