separate function for inverse interpolation of X given desired Y

1 files changed, 27 insertions, 11 deletions

diff --git a/device-functions.c b/device-functions.c
index 2bfd784..82d38e6 100644
--- a/device-functions.c
+++ b/device-functions.c
@@ -581,6 +581,8 @@ int Set_Pw(int check_possible_only,int word_override,int range_override,int chan
 	globals.ChannelState[channel].pw=set_pw;
 	Set_Update_Chans();
 
+	g_print_debug("pw range %d, word %d\n",relay_range,word_out);
+
 	if (!called_from_set_ampl) {
 		Set_Amplitude(0,0,0,0,0,0,channel,globals.ChannelState[channel].amplitude,1);
 	}
@@ -2483,14 +2485,36 @@ int Set_VI_Del_Cal(int parameter,int channel,int calibration_point_number)
 
 static int linear_interpolation (int x1, int x2, float y1, float y2, float y_need)
 {
+	if ((y2 == y1) || (x2 = x1)) {
+		return -1;
+	}
+
 	return (int) ( (y_need - y1) / (y2 - y1) * (float) (x2 - x1) ) + x1;
 }
 
 
+static int inverse_interpolation (int x1, int x2, float y1, float y2, float y_need)
+{
+	// assuming y = B / (x - A)
+	// A, B = constants
+	// x = word
+	// y = output
+
+	if ((y1 == y2) || (y_need == 0.0)) {
+		return -1;
+	}
+
+	float A = ((y1 * x1) - (y2 * x2)) / (y1 - y2);
+	float B = y1 * (x1 - A);
+
+	return (int) (A + (B / y_need));
+}
+
+
 int Set_VI_Control(int parameter,int channel,float new_ampl,int *point_found,int *relay_range,int *atten_range,
                    int *UseNegData,int *entry,int *word_out,int *actual_pol)
 {
-	float use_ampl,tweaked_use_ampl,fraction;
+	float use_ampl,tweaked_use_ampl;
 	int i;
 	float min_os_in_range,max_os_in_range;
 	float min_ampl_in_range,max_ampl_in_range;
@@ -2500,7 +2524,6 @@ int Set_VI_Control(int parameter,int channel,float new_ampl,int *point_found,int
 	short *pwl_vc;
 	int index,use_range;
 	int range_i,entry_i;
-	float inverse_word_out;
 	int pw_polarity;
 
 	float pw_distort_val;
@@ -2841,7 +2864,6 @@ int Set_VI_Control(int parameter,int channel,float new_ampl,int *point_found,int
 						}
 					}
 
-					fraction = (tweaked_use_ampl-pwlamp1) / (pwlamp1 - pwlamp2);
 					*relay_range=range_i;
 					*entry=entry_i;
 
@@ -2863,9 +2885,7 @@ int Set_VI_Control(int parameter,int channel,float new_ampl,int *point_found,int
 					// Normally just the first range is voltage-controlled.
 
 					if (reciprocal_relationship) {
-						inverse_word_out = fraction * (1.0/((float) pwl_vc[index]) - 1.0/((float) pwl_vc[index+1]));
-						inverse_word_out+=1/((float) pwl_vc[index]);
-						*word_out=(int) (1.0/inverse_word_out);
+						*word_out = inverse_interpolation (pwl_vc[index], pwl_vc[index+1], pwlamp1, pwlamp2, tweaked_use_ampl);
 					} else {
 						*word_out = linear_interpolation (pwl_vc[index], pwl_vc[index+1], pwlamp1, pwlamp2, tweaked_use_ampl);
 					}
@@ -2914,14 +2934,10 @@ int Set_VI_Control(int parameter,int channel,float new_ampl,int *point_found,int
 			                && (fabs(pwl_amp[index+1])>smallest_allowed_number)
 			                && (fabs(pwl_amp[index]-pwl_amp[index+1])>smallest_allowed_number)	) {
 				*point_found=1;
-
-				fraction = (tweaked_use_ampl-pwl_amp[index]) / (pwl_amp[index] - pwl_amp[index+1]);
 				*relay_range=use_range;
 				*entry=entry_i;
 
-				inverse_word_out = fraction * (1.0/((float) pwl_vc[index]) - 1.0/((float) pwl_vc[index+1]));
-				inverse_word_out+=1/((float) pwl_vc[index]);
-				*word_out=(int) (1.0/inverse_word_out);
+				*word_out = inverse_interpolation (pwl_vc[index], pwl_vc[index+1], pwl_amp[index], pwl_amp[index+1], tweaked_use_ampl);
 			}
 		}
 	}