added flex program that allows selection of fractional precision

integer.c

@@ -17,6 +17,9 @@ void prt(short c, short s) {
    printf("c=%d dec/%02d trunc dec / %02x\n", c, 0xff & c, 0xff & c);
 }
 
+short s(short i) {
+  return i;
+}
 
 int main(int argc, char* argv[])
 {
@@ -34,20 +37,20 @@ int main(int argc, char* argv[])
     short px=0;
     while (px < width*zoom) {
       // $380 = 3.5      $240=2.25    $180=1.5     $300=3
-      short x0 = (((px*0x380)/zoom) >> 5) - 0x240;
-      short y0 = (((py*0x300)/zoom) / 22) - 0x180;
+      short x0 = s(s(s(px*0x380)/zoom) >> 5) - 0x240;
+      short y0 = s(s(s(py*0x300)/zoom) / 22) - 0x180;
 
       short x=0;
       short y=0;
 
       short i=0;
 
-
       short xSqr;
       short ySqr;
       while (i < iters) {
-        xSqr = (x * x) >> 8;
-        ySqr = (y * y) >> 8;
+        xSqr = s(x * x) >> 8;
+        ySqr = s(y * y) >> 8;
+
 
         if (i == 1 && px == 1 && py == 0) 
             prt(x, xSqr);
@@ -57,7 +60,7 @@ int main(int argc, char* argv[])
         }
 
         short xt = xSqr - ySqr + x0;
-        y = (((x * y)>>8) * 2 ) + y0;
+        y = (s(s(x * y)>>8) * 2 ) + y0;
         x=xt;
 
         i = i + 1;

integerFlex.c

@@ -35,21 +35,27 @@ short toPrec(double f, int bitsPrecision) {
   printf(" %3f -> %3d 0x%04x  %c%c %c%c%c%c%c%c%c%c\n",f, ret, ret, BYTE_TO_BINARY(ret));
   return ret;
 }
+short s(short i) {
+  return i;
+}
+
 
 int main(int argc, char* argv[])
 {
+  short log=0;
+  short logFrom=27;
+
   // chosen to match https://www.youtube.com/watch?v=DC5wi6iv9io
-  short width = 32; // basic width of a zx81
-  short height = 22; // basic width of a zx81
-  short zoom=1;  // bigger with finer detail ie a smaller step size - leave at 1 for 32x22
+  int width = 32; // basic width of a zx81
+  int height = 22; // basic width of a zx81
+  int zoom=1;  // bigger with finer detail ie a smaller step size - leave at 1 for 32x22
 
   // params 
   short bitsPrecision = 6;
   printf("DECS=%d\n", bitsPrecision);
 
   short X1 = toPrec(3.5,bitsPrecision) / zoom;
   short X2 = toPrec(2.25,bitsPrecision) ;
-
   short Y1 = toPrec(3,bitsPrecision)/zoom ;   // horiz pos
   short Y2 = toPrec(1.5,bitsPrecision) ; // vert pos
   short LIMIT = toPrec(4,bitsPrecision);
@@ -64,41 +70,80 @@ int main(int argc, char* argv[])
     short px=0;
     while (px < width*zoom) {
 
-      short x0 = (short)(((short)(px*X1)) / width) - X2;
-      short y0 = (short)(((short)(py*Y1)) / height) - Y2;
+      short x0 = s(s(px*X1) / width) - X2;
+      short y0 = s(s(py*Y1) / height) - Y2;
+
+      if (x0 +y0 != 0) {
+  //      printf("px=%4x ", px); printf("py=%4x ", py); printf("x0=%4x ", x0); printf("y0=%4x\n", y0);
+      }
 
       short x=0;
       short y=0;
 
       short i=0;
 
+if (0 && log >= logFrom) {
+  printf("\n-------\n");
+  printf("x0=%4x\n", x0&0xffff);
+  printf("y0=%4x\n", y0&0xffff);
+}
 
       short xSqr;
       short ySqr;
       while (i < iters) {
-        xSqr = ((short)(x * x)) >> bitsPrecision;
-        ySqr = ((short)(y * y)) >> bitsPrecision;
+        xSqr = s(x * x) >> bitsPrecision;
+        ySqr = s(y * y) >> bitsPrecision;
+
+if (0 && log >= logFrom) {
+  printf("x =%4x\n", x&0xffff);
+  printf("x2=%4x\n", (xSqr)&0xffff);
+  printf("y =%4x\n", y&0xffff);
+  printf("y2=%4x\n", (ySqr)&0xffff);
+  printf("xsq+ysq=%4x\n", (xSqr+ySqr)&0xffff);
+  printf("\n");
+}
+
 
         // breakout also if negative as this indicates overflow of the addition which is a fault
         if ((xSqr + ySqr) > LIMIT || (xSqr+ySqr) < 0) {
           break;
         }
 
         short xt = xSqr - ySqr + x0;
-        y = ((((short)(x * y)) >> bitsPrecision) * 2 ) + y0;
-        x=xt;
 
+if (0 && log >= logFrom) {
+  printf("i    =%4x\n", i);
+  printf("diff =%4x\n", (xSqr-ySqr)&0xffff);
+  printf("xt   =%4x\n", (xt)&0xffff);
+
+  short xy = x*y;
+  printf("x*y         =%4x * %4x\n", (x)&0xffff, (y)&0xffff);
+  printf("x*y         =%4x\n", (xy)&0xffff);
+  printf("x*y>6       =%4x\n", (xy >> 6)&0xffff);
+  printf("x*y>6 << 1  =%4x\n", ((short)(xy >> 6) * 2)&0xffff);
+  printf("x*y>6<<1+y0 =%4x\n", (((short)((short)(xy >> 6)) << 2)+ y0)&0xffff);
+}
+
+        y = s(s(s(x * y) >> bitsPrecision) * 2) + y0;
+        x=xt;
         i = i + 1;
 
       }
+if (0 && log >= logFrom) {
+  printf("x=%4x  ", x&0xffff);
+  printf("xsqr=%4x\n", xSqr&0xffff);
+  exit(1);
+}
 
 
       i = i - 1;
 
+
       printf("%c", chr[i]);
 
       px = px + 1;
 
+      log ++;
     }
 
     printf("\n");