whoops

now produces correct fractal but iterations outside are
sometimes wrong
probably range errrs in intermediate calc

mandel.s

@@ -397,7 +397,7 @@ neg2:
 
 positive:
     inc arg + 2  ; 5 cyc
-    beq next     ; 2 cyc
+    bne next     ; 2 cyc
     inc arg + 3  ; 5 cyc
 
 zero:
@@ -436,11 +436,16 @@ keep_going:
 
     .macro quick_exit arg
         .local keep_going
+        .local keep_going2
         lda arg + 1
         cmp #(4 << 4)
         bmi keep_going
         rts
     keep_going:
+        cmp #(256 - (4 << 4))
+        bpl keep_going2
+        rts
+    keep_going2:
     .endmacro
 
     ; 4.12: (-8 .. +7.9)
@@ -452,18 +457,19 @@ keep_going:
     ; zy = zx_zy + zx_zy + cy
     add16 zy, zx_zy, zx_zy
     add16 zy, zy, cy
+    quick_exit zy
 
     ; zx_2 = zx * zx
     imul16_round zx_2, zx, zx, 4
-    quick_exit dist
+    quick_exit zx_2
 
     ; zy_2 = zy * zy
     imul16_round zy_2, zy, zy, 4
-    quick_exit dist
+    quick_exit zy_2
 
     ; zx_zy = zx * zy
     imul16_round zx_zy, zx, zy, 4
-    quick_exit dist
+    quick_exit zx_zy
 
     ; dist = zx_2 + zy_2
     add16 dist, zx_2, zy_2