Hopefully this will fix the build errors

src/sound/filter.c

@@ -132,3 +132,103 @@ filter* filter_lp_fir_alloc(double freq, int order) {
 
 	return f;
 }
+
+
+void filter2_setup(int type, double fc, double d, double gain,
+					struct filter2_context *filter)
+{
+	double w;	/* cutoff freq, in radians/sec */
+	double w_squared;
+	double den;	/* temp variable */
+	double two_over_T = 2*Machine->sample_rate;
+	double two_over_T_squared = two_over_T * two_over_T;
+
+	/* calculate digital filter coefficents */
+	/*w = 2.0*M_PI*fc; no pre-warping */
+	w = Machine->sample_rate*2.0*tan(M_PI*fc/Machine->sample_rate); /* pre-warping */
+	w_squared = w*w;
+
+	den = two_over_T_squared + d*w*two_over_T + w_squared;
+
+	filter->a1 = 2.0*(-two_over_T_squared + w_squared)/den;
+	filter->a2 = (two_over_T_squared - d*w*two_over_T + w_squared)/den;
+
+	switch (type)
+	{
+		case FILTER_LOWPASS:
+			filter->b0 = filter->b2 = w_squared/den;
+			filter->b1 = 2.0*(filter->b0);
+			break;
+		case FILTER_BANDPASS:
+			filter->b0 = d*w*two_over_T/den;
+			filter->b1 = 0.0;
+			filter->b2 = -(filter->b0);
+			break;
+		case FILTER_HIGHPASS:
+			filter->b0 = filter->b2 = two_over_T_squared/den;
+			filter->b1 = -2.0*(filter->b0);
+			break;
+		default:
+			logerror("filter2_setup() - Invalid filter type for 2nd order filter.");
+			break;
+	}
+
+    filter->b0 *= gain;
+    filter->b1 *= gain;
+    filter->b2 *= gain;
+}
+
+
+/* Reset the input/output voltages to 0. */
+void filter2_reset(struct filter2_context *filter)
+{
+	filter->x0 = 0;
+	filter->x1 = 0;
+	filter->x2 = 0;
+	filter->y0 = 0;
+	filter->y1 = 0;
+	filter->y2 = 0;
+}
+
+
+/* Step the filter. */
+void filter2_step(struct filter2_context *filter)
+{
+	filter->y0 = -filter->a1 * filter->y1 - filter->a2 * filter->y2 +
+	                filter->b0 * filter->x0 + filter->b1 * filter->x1 + filter->b2 * filter->x2;
+	filter->x2 = filter->x1;
+	filter->x1 = filter->x0;
+	filter->y2 = filter->y1;
+	filter->y1 = filter->y0;
+}
+
+
+/* Setup a filter2 structure based on an op-amp multipole bandpass circuit. */
+void filter_opamp_m_bandpass_setup(double r1, double r2, double r3, double c1, double c2,
+					struct filter2_context *filter)
+{
+	double	r_in, fc, d, gain;
+
+	if (r1 == 0)
+	{
+		logerror("filter_opamp_m_bandpass_setup() - r1 can not be 0");
+		return;	/* Filter can not be setup.  Undefined results. */
+	}
+
+	if (r2 == 0)
+	{
+		gain = 1;
+		r_in = r1;
+	}
+	else
+	{
+		gain = r2 / (r1 + r2);
+		r_in = 1.0 / (1.0/r1 + 1.0/r2);
+	}
+
+	fc = 1.0 / (2 * M_PI * sqrt(r_in * r3 * c1 * c2));
+	d = (c1 + c2) / sqrt(r3 / r_in * c1 * c2);
+	gain *= -r3 / r_in * c2 / (c1 + c2);
+
+	filter2_setup(FILTER_BANDPASS, fc, d, gain, filter);
+}