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.  There are two different
  11    sets of parameters: one set for 30-bit digits, stored in an unsigned 32-bit
  12    integer type, and one set for 15-bit digits with each digit stored in an
  13    unsigned short.  The value of PYLONG_BITS_IN_DIGIT, defined either at
  14    configure time or in pyport.h, is used to decide which digit size to use.
  15
  16    Type 'digit' should be able to hold 2*PyLong_BASE-1, and type 'twodigits'
  17    should be an unsigned integer type able to hold all integers up to
  18    PyLong_BASE*PyLong_BASE-1.  x_sub assumes that 'digit' is an unsigned type,
  19    and that overflow is handled by taking the result modulo 2**N for some N >
  20    PyLong_SHIFT.  The majority of the code doesn't care about the precise
  21    value of PyLong_SHIFT, but there are some notable exceptions:
  22
  23    - long_pow() requires that PyLong_SHIFT be divisible by 5
  24
  25    - PyLong_{As,From}ByteArray require that PyLong_SHIFT be at least 8
  26
  27    - long_hash() requires that PyLong_SHIFT is *strictly* less than the number
  28      of bits in an unsigned long, as do the PyLong <-> long (or unsigned long)
  29      conversion functions
  30
  31    - the long <-> size_t/Py_ssize_t conversion functions expect that
  32      PyLong_SHIFT is strictly less than the number of bits in a size_t
  33
  34    - the marshal code currently expects that PyLong_SHIFT is a multiple of 15
  35
  36   The values 15 and 30 should fit all of the above requirements, on any
  37   platform.
  38 */
  39
  40 #if PYLONG_BITS_IN_DIGIT == 30
  41 #if !(defined HAVE_UINT64_T && defined HAVE_UINT32_T &&          \
  42       defined HAVE_INT64_T && defined HAVE_INT32_T)
  43 #error "30-bit long digits requested, but the necessary types are not available on this platform"
  44 #endif
  45 typedef PY_UINT32_T digit;
  46 typedef PY_INT32_T sdigit; /* signed variant of digit */
  47 typedef PY_UINT64_T twodigits;
  48 typedef PY_INT64_T stwodigits; /* signed variant of twodigits */
  49 #define PyLong_SHIFT    30
  50 #elif PYLONG_BITS_IN_DIGIT == 15
  51 typedef unsigned short digit;
  52 typedef short sdigit; /* signed variant of digit */
  53 typedef unsigned long twodigits;
  54 typedef long stwodigits; /* signed variant of twodigits */
  55 #define PyLong_SHIFT    15
  56 #else
  57 #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
  58 #endif
  59 #define PyLong_BASE     ((digit)1 << PyLong_SHIFT)
  60 #define PyLong_MASK     ((digit)(PyLong_BASE - 1))
  61
  62 /* b/w compatibility with Python 2.5 */
  63 #define SHIFT   PyLong_SHIFT
  64 #define BASE    PyLong_BASE
  65 #define MASK    PyLong_MASK
  66
  67 #if PyLong_SHIFT % 5 != 0
  68 #error "longobject.c requires that PyLong_SHIFT be divisible by 5"
  69 #endif
  70
  71 /* Long integer representation.
  72    The absolute value of a number is equal to
  73         SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
  74    Negative numbers are represented with ob_size < 0;
  75    zero is represented by ob_size == 0.
  76    In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
  77    digit) is never zero.  Also, in all cases, for all valid i,
  78         0 <= ob_digit[i] <= MASK.
  79    The allocation function takes care of allocating extra memory
  80    so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
  81
  82    CAUTION:  Generic code manipulating subtypes of PyVarObject has to
  83    aware that longs abuse  ob_size's sign bit.
  84 */
  85
  86 struct _longobject {
  87         PyObject_VAR_HEAD
  88         digit ob_digit[1];
  89 };
  90
  91 PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
  92
  93 /* Return a copy of src. */
  94 PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
  95
  96 #ifdef __cplusplus
  97 }
  98 #endif
  99 #endif /* !Py_LONGINTREPR_H */