CSUSM FM Synth 2017 / Mbed 2 deprecated FMSynthCSUSM

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Dependencies:   mbed

Fork of STM32FMSynth by Steven Clark

Diff: main.cpp

Revision:
5:ac5c4bd3ef4b
Parent:
4:1d2a699c95c7
Child:
6:9f8c8c3c111d
--- a/main.cpp	Wed Nov 29 02:34:59 2017 +0000
+++ b/main.cpp	Wed Nov 29 21:47:56 2017 +0000
@@ -77,10 +77,28 @@
 int carR;
 
 int fastSin(const int phase){
-    int i = phase >> 2;
+    int index = (phase & 0x3ffc) >> 2;
+    int subindex = phase & 0x3;
+    int quadrant = (phase & 0xc000) >> 14;
     int sum = 0;
-    sum += (phase & 0x3) * sintable[i+1];
-    sum += (0x4 - (phase & 0x3)) * sintable[i];
+    switch (quadrant) {
+        case 0:
+            sum += (4 - subindex) * sintable[index];
+            sum += subindex * sintable[index+1];
+            break;
+        case 1:
+            sum += (4 - subindex) * sintable[1+4096-index];
+            sum += subindex * sintable[4096-index];
+            break;
+        case 2:
+            sum -= (4 - subindex) * sintable[index];
+            sum -= subindex * sintable[index+1];        
+            break;
+        case 3:
+            sum -= (4 - subindex) * sintable[1+4096-index];
+            sum -= subindex * sintable[4096-index];
+            break;
+    }
     sum = sum >> 2;
     
     return sum;