Write a program (or explain how to do it) that will display a descending "spiral" of NxN numbers, using constant space (no arrays allowed). For example, here's what the spiral looks like for N=10:

   99    98    97    96    95    94    93    92    91    90
   64    63    62    61    60    59    58    57    56    89
   65    36    35    34    33    32    31    30    55    88
   66    37    16    15    14    13    12    29    54    87
   67    38    17     4     3     2    11    28    53    86
   68    39    18     5     0     1    10    27    52    85
   69    40    19     6     7     8     9    26    51    84
   70    41    20    21    22    23    24    25    50    83
   71    42    43    44    45    46    47    48    49    82
   72    73    74    75    76    77    78    79    80    81