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   1 #include "postgres.h"
   2 #include "fmgr.h"
   3
   4 PG_FUNCTION_INFO_V1(my_factorial);
   5
   6 Datum
   7 my_factorial(PG_FUNCTION_ARGS)
   8 {
   9         int32 res, n = PG_GETARG_INT32(0);
  10         Datum d;
  11
  12         if (n < 0)
  13                 elog(ERROR, "Так нельзя!");
  14
  15         if (n == 0)
  16                 PG_RETURN_INT32(1);
  17
  18         d = DirectFunctionCall1(my_factorial, Int32GetDatum(n - 1));
  19
  20         res = DatumGetInt32(d) * n;
  21
  22         PG_RETURN_INT32(res);
  23 }
  24