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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