Include/longintrepr.h

   1 #ifndef Py_LONGINTREPR_H
   2 #define Py_LONGINTREPR_H
   3 #ifdef __cplusplus
   4 extern "C" {
   5 #endif
   6
   7
   8 /* This is published for the benefit of "friend" marshal.c only. */
   9
  10 /* Parameters of the long integer representation.
  11    These shouldn't have to be changed as C should guarantee that a short
  12    contains at least 16 bits, but it's made changeable anyway.
  13    Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits'
  14    should be able to hold the intermediate results in 'mul'
  15    (at most (BASE-1)*(2*BASE+1) == MASK*(2*MASK+3)).
  16    Also, x_sub assumes that 'digit' is an unsigned type, and overflow
  17    is handled by taking the result mod 2**N for some N > SHIFT.
  18    And, at some places it is assumed that MASK fits in an int, as well.
  19    long_pow() requires that SHIFT be divisible by 5. */
  20
  21 typedef unsigned short digit;
  22 typedef unsigned int wdigit; /* digit widened to parameter size */
  23 #define BASE_TWODIGITS_TYPE long
  24 typedef unsigned BASE_TWODIGITS_TYPE twodigits;
  25 typedef BASE_TWODIGITS_TYPE stwodigits; /* signed variant of twodigits */
  26
  27 #define SHIFT   15
  28 #define BASE    ((digit)1 << SHIFT)
  29 #define MASK    ((int)(BASE - 1))
  30
  31 #if SHIFT % 5 != 0
  32 #error "longobject.c requires that SHIFT be divisible by 5"
  33 #endif
  34
  35 /* Long integer representation.
  36    The absolute value of a number is equal to
  37         SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
  38    Negative numbers are represented with ob_size < 0;
  39    zero is represented by ob_size == 0.
  40    In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
  41    digit) is never zero.  Also, in all cases, for all valid i,
  42         0 <= ob_digit[i] <= MASK.
  43    The allocation function takes care of allocating extra memory
  44    so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
  45
  46    CAUTION:  Generic code manipulating subtypes of PyVarObject has to
  47    aware that longs abuse  ob_size's sign bit.
  48 */
  49
  50 struct _longobject {
  51         PyObject_VAR_HEAD
  52         digit ob_digit[1];
  53 };
  54
  55 PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
  56
  57 /* Return a copy of src. */
  58 PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
  59
  60 #ifdef __cplusplus
  61 }
  62 #endif
  63 #endif /* !Py_LONGINTREPR_H */