smalltalk: mandelbrot + literal-array mutability fix

lib/smalltalk/tests/programs/mandelbrot.st

@@ -0,0 +1,36 @@
+"Mandelbrot — escape-time iteration of z := z² + c starting at z₀ = 0.
+ Returns the number of iterations before |z|² exceeds 4, capped at
+ maxIter. Classic-corpus program for the Smalltalk-on-SX runtime."
+
+Object subclass: #Mandelbrot
+  instanceVariableNames: ''!
+
+!Mandelbrot methodsFor: 'iteration'!
+escapeAt: cx and: cy maxIter: maxIter
+  | zx zy zx2 zy2 i |
+  zx := 0. zy := 0.
+  zx2 := 0. zy2 := 0.
+  i := 0.
+  [(zx2 + zy2 < 4) and: [i < maxIter]] whileTrue: [
+    zy := (zx * zy * 2) + cy.
+    zx := zx2 - zy2 + cx.
+    zx2 := zx * zx.
+    zy2 := zy * zy.
+    i := i + 1].
+  ^ i!
+
+inside: cx and: cy maxIter: maxIter
+  ^ (self escapeAt: cx and: cy maxIter: maxIter) >= maxIter! !
+
+!Mandelbrot methodsFor: 'grid'!
+countInsideRangeX: x0 to: x1 stepX: dx rangeY: y0 to: y1 stepY: dy maxIter: maxIter
+  | x y count |
+  count := 0.
+  y := y0.
+  [y <= y1] whileTrue: [
+    x := x0.
+    [x <= x1] whileTrue: [
+      (self inside: x and: y maxIter: maxIter) ifTrue: [count := count + 1].
+      x := x + dx].
+    y := y + dy].
+  ^ count! !