Much investigation of bignum problems

bignum multiply is still not working, but as bignum read and bignum divide depend on it, it's the problem to hit first.

lisp/scratchpad2.lisp

@@ -0,0 +1,84 @@
+"This demonstrates that although the print representation of three cell bignums blows up, the internal representation is sane"
+
+"We start by adding 8 copies of 2^60 - i.e. the first two-cell integer"
+
+(set! a
+  (+
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976
+    1152921504606846976))
+
+"Then repeatedly add eight copies of the previous generation"
+
+(set! b (+ a a a a a a a a))
+
+(set! c (+ b b b b b b b b))
+
+(set! d (+ c c c c c c c c))
+
+(set! e (+ d d d d d d d d))
+
+(set! f (+ e e e e e e e e))
+
+(set! g (+ f f f f f f f f))
+
+(set! h (+ g g g g g g g g))
+
+(set! i (+ h h h h h h h h))
+
+(set! j (+ i i i i i i i i))
+
+(set! k (+ j j j j j j j j))
+
+(set! l (+ k k k k k k k k))
+
+(set! m (+ l l l l l l l l))
+
+(set! n (+ m m m m m m m m))
+
+(set! o (+ n n n n n n n n))
+
+"p"
+(set! p (+ o o o o o o o o))
+
+"q"
+(set! q (+ p p p p p p p p))
+
+"r"
+(set! r (+ q q q q q q q q))
+
+"s"
+(inspect
+ (set! s (+ r r r r r r r r)))
+
+"t - first three cell integer. Printing blows up here"
+(inspect
+ (set! t (+ s s s s s s s s)))
+
+"u"
+(inspect
+ (set! u (+ t t t t t t t t)))
+
+"v"
+(inspect
+ (set! v (+ u u u u u u u u)))
+
+"w"
+(inspect
+ (set! w (+ v v v v v v v v)))
+
+(inspect
+ (set! x (+ w w w w w w w w)))
+
+(inspect
+ (set! y (+ x x x x x x x x)))
+
+(inspect
+ (set! z (+ y y y y y y y y)))
+
+(inspect (+ z z z z z z z z))