Add a little Rust tool to generate the initial values for the steppin…

…g width

derive_stepping.rs

@@ -1,4 +1,11 @@
 // ***********************************
+// This program can be used to derive the default stepping width
+// for X16_mandelbrot. It calcuates the the stepping width depending
+// on the section of the complex plane that should be visualized and
+// the resolution of the target machine. The output can be used
+// by the fixed point arithmetic as implemented in the assembly
+// part of the software.
+//
 // Change here for new values
 // ***********************************
 
@@ -11,7 +18,7 @@ const Y_LOWER_RIGHT: f64 = -Y_UPPER_LEFT;
 // Resolution in X and Y direction
 const PIXELS_X: f64 = 320.0;
 const PIXELS_Y: f64 = 240.0;
-// Accuracy in bytes after the comma
+// Accuracy in bytes without the sign byte
 const NUM_FIXED_BYTES: u16 = 4;
 
 fn print_mandel_fixed_point(f_in: f64) {
@@ -31,6 +38,7 @@ fn print_mandel_fixed_point(f_in: f64) {
         bit_count += 1;
     }
 
+    // Also adapt this statement if you change NUM_FIXED_BYTES.
     println!("{:06x}", res);
 }
 

makefile

@@ -3,6 +3,8 @@
 
 all: mandelbr.prg
 
+deriver: derive_stepping
+
 ifdef MAC
 ACME=../acme/acme
 WORKDIR=/Users/martin/data/X16_mandelbrot
@@ -14,6 +16,10 @@ endif
 clean:
 	rm $(WORKDIR)/mandelbr.prg
 	rm $(WORKDIR)/mandelbr.txt
+	rm $(WORKDIR)/derive_stepping
 
 mandelbr.prg: main.a arith16.a arith32.a string.a vera.a mandelhelp.a zeropage.a tests.a memory.a disk_io.a rtc.a
 	$(ACME) -l $(WORKDIR)/mandelbr.txt $(WORKDIR)/main.a
+
+derive_stepping: derive_stepping.rs
+	rustc derive_stepping.rs

vera.a

@@ -91,6 +91,7 @@ drawPoint
     lda NUM_ITER
     cmp MAX_ITER
     beq .plotBlack
+    clc
     adc #47
     sta VERA_DATA_0
     rts