better rad-to-theta angle conversion impl

engine/include/libgba-sprite-engine/math.h

@@ -21,6 +21,7 @@ extern FIXED HALF;
 extern FIXED ONE;
 extern FIXED TWO;
 
+#define SIN_LUT_MAX ((512 << 6) * 2)            // 65536, FFFFh range
 #define FIX12_SHIFT 12
 #define FIX12_SCALE ( 1<<FIX12_SHIFT		)
 
@@ -53,7 +54,7 @@ INLINE float gr2rad(uint grad) {
 }
 
 INLINE FIXED gr2lut(uint grad) {
-    return 65535 / (360 / (grad % 360));
+    return SIN_LUT_MAX / (360 / (grad % 360));
 }
 
 INLINE FIXED rad2lut(float rad) {
@@ -61,8 +62,9 @@ INLINE FIXED rad2lut(float rad) {
 }
 
 INLINE FIXED fxrad2lut(FIXED rad) {
-    // TODO NOT good; too much divisions, but hey, fuck it
-    return rad2lut(fx2float(rad));
+    // TODO could be better without fx2float() ?
+    int scale = fx2float(rad) / (2*M_PI / 512);
+    return (scale << 6) * 2;
 }
 
 INLINE float fx12ToFloat(FIXED fx) {

test/fixedpoinmathtest.cpp

@@ -40,6 +40,23 @@ TEST_F(FpSuite, LUTValueTests) {
     ASSERT_EQ(rnd(sinLutConv8), 0.995f);
 }
 
+TEST_F(FpSuite, SinLookupTests) {
+    int degrees = 360;
+    float radians = gr2rad(degrees);
+    std::cout << degrees << " in rad " << radians << std::endl;
+
+    float sinhalf = sin(radians);
+    ASSERT_FLOAT_EQ(rnd(sinhalf), 0.0049999999);
+
+    float sinlumax = fx2float(fx12Tofx8(lu_sin(SIN_LUT_MAX)));
+    ASSERT_FLOAT_EQ(rnd(sinlumax), 0.0049999999);
+
+    int scale = radians / (2*M_PI / 512);
+    FIXED theta = (scale << 6) * 2;
+    float sinlu = fx2float(fx12Tofx8(lu_sin(theta)));
+    ASSERT_FLOAT_EQ(rnd(sinlu), 0.0049999999);
+}
+
 TEST_F(FpSuite, TanFromFixedPointRadian) {
     // 20 degrees is 0.34906577777777775 rad
     // will be stored as .8f as input val