Fixed ASTC GPU shader

src/video_core/host_shaders/astc_decoder.comp

@@ -731,18 +731,46 @@ uint UnquantizeTexelWeight(EncodingData val) {
     const uint bitlen = NumBits(val);
     const uint bitval = BitValue(val);
 
+    // I probably added this wrong, brain empty atm
     if (encoding == JUST_BITS) {
         uint z = bitval;
+        uint x = bitlen;
         switch (bitlen) {
-            case 1: return z * 64;
-            case 2: return uint(floor(float(z) * 21.5f));
-            case 3: return uint(floor(float(z) * 9.25f));
-            case 4: return uint(floor(float(z) * 4.125f));
-            case 5: return uint(floor(float(z) * 2.0625f));
-            default: return FastReplicateTo6(z, bitlen);
+            case 1:
+                return z * 64;
+            case 2:
+            case 3:
+            case 4:
+            case 5:
+                return uint(floor(0.5f + float(z) * 64.0f / float((1 << x) - 1)));
+            default:
+                return FastReplicateTo6(z, bitlen);
         }
     }
     
+    // Brain screaming at me that division is expensive, probably ultra wrong so have this here incase
+    /*if (encoding == JUST_BITS) {
+        uint z = bitval;
+        switch (bitlen) {
+            case 1: return z * 64;
+
+            case 2: // (z * 64 + 1) / 3
+                return ((z * 64 + 1) * 43691) >> 17;
+
+            case 3: // (z * 64 + 3) / 7
+                return ((z * 64 + 3) * 37449) >> 18;
+
+            case 4: // (z * 64 + 7) / 15
+                return ((z * 64 + 7) * 34953) >> 19;
+
+            case 5: // (z * 64 + 15) / 31
+                return ((z * 64 + 15) * 33826) >> 20;
+
+            default:
+                return FastReplicateTo6(z, bitlen);
+        }
+    }*/
+    
     const uint A = ReplicateBitTo7((bitval & 1));
     uint B = 0, C = 0, D = 0;
     uint result = 0;