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      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 #define _PyLong_DECIMAL_SHIFT	9 /* max(e such that 10**e fits in a digit) */
     51 #define _PyLong_DECIMAL_BASE	((digit)1000000000) /* 10 ** DECIMAL_SHIFT */
     52 #elif PYLONG_BITS_IN_DIGIT == 15
     53 typedef unsigned short digit;
     54 typedef short sdigit; /* signed variant of digit */
     55 typedef unsigned long twodigits;
     56 typedef long stwodigits; /* signed variant of twodigits */
     57 #define PyLong_SHIFT	15
     58 #define _PyLong_DECIMAL_SHIFT	4 /* max(e such that 10**e fits in a digit) */
     59 #define _PyLong_DECIMAL_BASE	((digit)10000) /* 10 ** DECIMAL_SHIFT */
     60 #else
     61 #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
     62 #endif
     63 #define PyLong_BASE	((digit)1 << PyLong_SHIFT)
     64 #define PyLong_MASK	((digit)(PyLong_BASE - 1))
     65 
     66 /* b/w compatibility with Python 2.5 */
     67 #define SHIFT	PyLong_SHIFT
     68 #define BASE	PyLong_BASE
     69 #define MASK	PyLong_MASK
     70 
     71 #if PyLong_SHIFT % 5 != 0
     72 #error "longobject.c requires that PyLong_SHIFT be divisible by 5"
     73 #endif
     74 
     75 /* Long integer representation.
     76    The absolute value of a number is equal to
     77    	SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
     78    Negative numbers are represented with ob_size < 0;
     79    zero is represented by ob_size == 0.
     80    In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
     81    digit) is never zero.  Also, in all cases, for all valid i,
     82    	0 <= ob_digit[i] <= MASK.
     83    The allocation function takes care of allocating extra memory
     84    so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
     85 
     86    CAUTION:  Generic code manipulating subtypes of PyVarObject has to
     87    aware that longs abuse  ob_size's sign bit.
     88 */
     89 
     90 struct _longobject {
     91 	PyObject_VAR_HEAD
     92 	digit ob_digit[1];
     93 };
     94 
     95 PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
     96 
     97 /* Return a copy of src. */
     98 PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
     99 
    100 #ifdef __cplusplus
    101 }
    102 #endif
    103 #endif /* !Py_LONGINTREPR_H */
    104