(external) bl00mbox/radspa: integer lowpass

tiny pull this time to investigate float core pinning.

components/bl00mbox/plugins/lowpass.c

 #include "lowpass.h"
 
+//#define LOWPASS_DEBUG_PRINT
+
+#ifdef LOWPASS_DEBUG_PRINT
+#include <stdio.h>
+#endif
+
 radspa_t * lowpass_create(uint32_t init_var);
 radspa_descriptor_t lowpass_desc = {
     .name = "lowpass",
@@ -16,79 +22,67 @@ radspa_descriptor_t lowpass_desc = {
 #define LOWPASS_Q 3
 #define LOWPASS_GAIN 4
 
-static float apply_lowpass(lowpass_data_t * data, int32_t input){
-    data->pos++;
-    if(data->pos >= 3) data->pos = 0;
-
-	float out = 0;
-    float in_acc = input;
-
-	for(int8_t i = 0; i<2; i++){
-        int8_t pos = data->pos - i - 1;
-        if(pos < 0) pos += 3;
-        in_acc += (2-i)*data->in_history[pos];
-
-        out -= (data->out_history[pos] * data->out_coeff[i]);
-    }
-    out += in_acc * data->in_coeff;
-
-    data->in_history[data->pos] = input;
-    data->out_history[data->pos] = out;
+#define LOWPASS_INTERNAL_SHIFT 14
+#define LOWPASS_OUT_COEFF_SHIFT 11
 
-	return out;
-}
-
-static uint8_t coeff_shift(float coeff) {
-    int32_t ret = 16;
+static void coeff_shift(uint64_t coeff, int32_t *shift, int32_t * shifted_coeff) {
+    int32_t ret = 22;
+    uint64_t ret_coeff = coeff >> (32-ret);
     while(1){
-        int32_t test_val = (1<<ret) * coeff;
-        if(test_val < 0) test_val = -test_val;
-        if(test_val > (1<<12)){
+        if(ret > 31){
+            ret = 31;
+            ret_coeff = coeff >> (32-ret);
+            break;
+        }
+        if(ret < (LOWPASS_INTERNAL_SHIFT)){
+            ret = (LOWPASS_INTERNAL_SHIFT);
+            ret_coeff = coeff >> (32-ret);
+            break;
+        }
+        if(ret_coeff > (1UL<<14)){
             ret -= 3;
-        } else if (test_val < (1<<8)){
+            ret_coeff = coeff >> (32-ret);
+        } else if (ret_coeff < (1UL<<11)){
             ret += 3;
+            ret_coeff = coeff >> (32-ret);
         } else {
             break;
         }
-        if(ret > 28) break;
-        if(ret < 4) break;
     }
-    return ret;
+    
+    * shift = ret;
+    * shifted_coeff = (int32_t) ret_coeff;
 }
 
-static void set_lowpass_coeffs(lowpass_data_t * data, float freq, float q){
-    //molasses, sorry
-    if(freq == 0) return;
-    if(q == 0) return;
-    float K = 2*48000;
-    float omega = freq * 6.28;
-    float A[3];
-    A[0] = K*K;
-    A[1] = K*omega/q;
+static void set_lowpass_coeffs(lowpass_data_t * data, int32_t freq, int32_t mq){
+    if(freq < 15.) freq = 15.;
+    if(freq > 15000.) freq = 15000.;
+    if(mq < 130) mq = 130;
+    int32_t K = 15287; // 2*48000/6.28
+    int32_t omega = freq;
+    int32_t A[3];
+    A[0] = K * K;
+    A[1] = K * 1000;
+    A[1] = (int64_t) A[1] * omega / (mq+1);
     A[2] = omega*omega;
-    float B = omega*omega;
-
-    float sum_a = A[0] + A[1] + A[2];
-
-    float round;
-    //int16_t shift;
+    int32_t sum_a = A[0] + A[1] + A[2];
+    int64_t round = A[2];
 
-    round = B / sum_a;
-    //shift = coeff_shift(round);
-    data->in_coeff = round;// * (1<<shift);
-    //data->in_coeff_shift = shift;
+    round = (round << 32) / sum_a;
+    int32_t shift;
+    int32_t shifted_coeff;
+    coeff_shift(round, &shift, &shifted_coeff);
+    data->in_coeff_shift = shift - (LOWPASS_INTERNAL_SHIFT);
+    data->in_coeff = shifted_coeff;
 
-    round = 2.*(A[2]-A[0]) / sum_a;
-    //shift = coeff_shift(round);
-    data->out_coeff[0] = round;// * (1<<shift);
-    //data->out_coeff_shift[0] = shift;
+    round = 2.*(A[2]-A[0]);
+    data->out_coeff[0] = round * (1LL<<(LOWPASS_OUT_COEFF_SHIFT)) / sum_a;
 
-    round = (A[0]-A[1]+A[2]) / sum_a;
-    //shift = coeff_shift(round);
-    data->out_coeff[1] = round;// * (1<<shift);
-    //data->out_coeff_shift[1] = shift;
+    round = (A[0]-A[1]+A[2]);
+    data->out_coeff[1] = round * (1LL<<(LOWPASS_OUT_COEFF_SHIFT)) / sum_a;
 }
 
+
 void lowpass_run(radspa_t * lowpass, uint16_t num_samples, uint32_t render_pass_id){
     radspa_signal_t * output_sig = radspa_signal_get_by_index(lowpass, LOWPASS_OUTPUT);
     if(output_sig->buffer == NULL) return;
@@ -102,16 +96,41 @@ void lowpass_run(radspa_t * lowpass, uint16_t num_samples, uint32_t render_pass_
         int16_t input = radspa_signal_get_value(input_sig, i, render_pass_id);
         int32_t freq = radspa_signal_get_value(freq_sig, i, render_pass_id);
         int16_t q = radspa_signal_get_value(q_sig, i, render_pass_id);
-        int16_t gain = radspa_signal_get_value(gain_sig, i, render_pass_id);
+        int32_t gain = radspa_signal_get_value(gain_sig, i, render_pass_id);
 
         if((freq != data->prev_freq) | (q != data->prev_q)){
-            set_lowpass_coeffs(data, freq, ((float) q + 1.)/1000.);
+            set_lowpass_coeffs(data, freq, q);
+#ifdef LOWPASS_DEBUG_PRINT
+            printf("\nfreq: %ld, q: %d\n", freq, q);
+            printf("in_coeff: %ld >> %ld, ", data->in_coeff, data->in_coeff_shift);
+            printf("out_coeffs: %ld, %ld\n", data->out_coeff[0], data->out_coeff[1]);
+#endif
             data->prev_freq = freq;
             data->prev_q = q;
         }
     
-        float out = apply_lowpass(data, input) + 0.5;
-        int16_t ret = radspa_clip(radspa_gain((int32_t) out, gain));
+        data->pos++;
+        if(data->pos >= 3) data->pos = 0;
+
+        data->in_history[data->pos] = input;
+
+        int32_t in_acc = input;
+        int32_t ret = 0;
+
+        for(int8_t i = 0; i<2; i++){
+            int8_t pos = data->pos - i - 1;
+            if(pos < 0) pos += 3;
+            in_acc += (2-i)*data->in_history[pos];
+
+            ret -= (((int64_t) data->out_history[pos]) * data->out_coeff[i]) >> (LOWPASS_OUT_COEFF_SHIFT);
+        }
+
+        ret += (in_acc * data->in_coeff) >> data->in_coeff_shift;
+
+        data->out_history[data->pos] = ret;
+
+        ret = ret >> (LOWPASS_INTERNAL_SHIFT);
+        ret = radspa_clip(radspa_gain(ret, gain));
         radspa_signal_set_value(output_sig, i, ret);
     }
 }