Just poking around and trying to remember where the problems are.

src/arith/integer.c

@@ -100,13 +100,12 @@ __int128_t cell_value( struct cons_pointer c, char op, bool is_first_cell ) {
 __int128_t int128_to_integer( __int128_t val,
                               struct cons_pointer less_significant,
                               struct cons_pointer new ) {
-    struct cons_pointer cursor = NIL;
     __int128_t carry = 0;
 
     if ( MAX_INTEGER >= val ) {
         carry = 0;
     } else {
-        carry = val >> 60;
+        carry = val >> INTEGER_BIT_SHIFT; 
         debug_printf( DEBUG_ARITH,
                       L"int128_to_integer: 64 bit overflow; setting carry to %ld\n",
                       ( int64_t ) carry );
@@ -136,7 +135,7 @@ struct cons_pointer make_integer_128( __int128_t val,
             less_significant =
                 make_integer( ( long int ) val & MAX_INTEGER,
                               less_significant );
-            val = val >> 60;
+            val = val >> INTEGER_BIT_SHIFT;
         }
 
     } while ( nilp( result ) );
@@ -290,7 +289,7 @@ struct cons_pointer multiply_integers( struct cons_pointer a,
 
                 /* if xj exceeds one digit, break it into the digit dj and
                  * the carry */
-                carry = xj >> 60;
+                carry = xj >> INTEGER_BIT_SHIFT;
                 struct cons_pointer dj = make_integer( xj & MAX_INTEGER, NIL );
 
                 /* destructively modify ri by appending dj */
@@ -320,7 +319,7 @@ struct cons_pointer multiply_integers( struct cons_pointer a,
 }
 
 /**
- * don't use; private to integer_to_string, and somewaht dodgy.
+ * don't use; private to integer_to_string, and somewhat dodgy.
  */
 struct cons_pointer integer_to_string_add_digit( int digit, int digits,
                                                  struct cons_pointer tail ) {
@@ -361,7 +360,7 @@ struct cons_pointer integer_to_string( struct cons_pointer int_pointer,
             while ( accumulator > 0 || !nilp( next ) ) {
                 if ( accumulator < MAX_INTEGER && !nilp( next ) ) {
                     accumulator +=
-                        ( pointer2cell( next ).payload.integer.value << 60 );
+                        ( pointer2cell( next ).payload.integer.value << INTEGER_BIT_SHIFT );
                     next = pointer2cell( next ).payload.integer.more;
                 }
                 int offset = ( int ) ( accumulator % base );

src/arith/peano.h

@@ -13,10 +13,18 @@
 #define PEANO_H
 
 /**
- * The maximum value we will allow in an integer cell.
+ * The maximum value we will allow in an integer cell: one less than 2^60:
+ * (let ((s (make-string-output-stream)))
+ *   (format s "0x0~XL" (- (expt 2 60) 1))
+ *   (string-downcase (get-output-stream-string s)))
+ *                              "0x0fffffffffffffffl"
+ * 
+ * So left shifting and right shifting by 60 bits is correct.
  */
 #define MAX_INTEGER ((__int128_t)0x0fffffffffffffffL)
 
+#define INTEGER_BIT_SHIFT (60)
+
 bool zerop( struct cons_pointer arg );
 
 struct cons_pointer negative( struct cons_pointer arg );

src/init.c

@@ -9,6 +9,7 @@
  * Licensed under GPL version 2.0, or, at your option, any later version.
  */
 
+#include <getopt.h>
 #include <locale.h>
 #include <stdbool.h>
 #include <stdio.h>

src/memory/conspage.c

@@ -267,6 +267,6 @@ void initialise_cons_pages(  ) {
 
 void summarise_allocation(  ) {
     fwprintf( stderr,
-              L"Allocation summary: allocated %lld; deallocated %lld.\n",
+              L"Allocation summary: allocated %lld; deallocated %lld; not deallocated %lld.\n",
-              total_cells_allocated, total_cells_freed );
+              total_cells_allocated, total_cells_freed, total_cells_allocated - total_cells_freed );
 }

src/memory/consspaceobject.h

@@ -478,6 +478,8 @@ struct free_payload {
  * exceeds 60 bits, the least significant 60 bits are stored in the first cell
  * in the chain, the next 60 in the next cell, and so on. Only the value of the
  * first cell in any chain should be negative.
+ * 
+ * \todo Why is this 60, and not 64 bits?
  */
 struct integer_payload {
     /** the value of the payload (i.e. 60 bits) of this cell. */

src/ops/lispops.c

@@ -681,6 +681,8 @@ bool end_of_stringp( struct cons_pointer arg ) {
  * returns a cell constructed from a and b. If a is of type string but its
  * cdr is nill, and b is of type string, then returns a new string cell;
  * otherwise returns a new cons cell.
+ * 
+ * Thus: `(cons "a" "bcd") -> "abcd"`, but `(cons "ab" "cd") -> ("ab" . "cd")`
  *
  * * (cons a b)
  *
@@ -700,7 +702,6 @@ lisp_cons( struct stack_frame *frame, struct cons_pointer frame_pointer,
         return NIL;
     } else if ( stringp( car ) && stringp( cdr ) &&
                 end_of_stringp( c_cdr( car ) ) ) {
-        // \todo check that car is of length 1
         result =
             make_string( pointer2cell( car ).payload.string.character, cdr );
     } else {