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longintrepr.h 3.7 KB

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  1. #ifndef Py_LIMITED_API
  2. #ifndef Py_LONGINTREPR_H
  3. #define Py_LONGINTREPR_H
  4. #ifdef __cplusplus
  5. extern "C" {
  6. #endif
  7. /* This is published for the benefit of "friends" marshal.c and _decimal.c. */
  8. /* Parameters of the integer representation. There are two different
  9. sets of parameters: one set for 30-bit digits, stored in an unsigned 32-bit
  10. integer type, and one set for 15-bit digits with each digit stored in an
  11. unsigned short. The value of PYLONG_BITS_IN_DIGIT, defined either at
  12. configure time or in pyport.h, is used to decide which digit size to use.
  13. Type 'digit' should be able to hold 2*PyLong_BASE-1, and type 'twodigits'
  14. should be an unsigned integer type able to hold all integers up to
  15. PyLong_BASE*PyLong_BASE-1. x_sub assumes that 'digit' is an unsigned type,
  16. and that overflow is handled by taking the result modulo 2**N for some N >
  17. PyLong_SHIFT. The majority of the code doesn't care about the precise
  18. value of PyLong_SHIFT, but there are some notable exceptions:
  19. - long_pow() requires that PyLong_SHIFT be divisible by 5
  20. - PyLong_{As,From}ByteArray require that PyLong_SHIFT be at least 8
  21. - long_hash() requires that PyLong_SHIFT is *strictly* less than the number
  22. of bits in an unsigned long, as do the PyLong <-> long (or unsigned long)
  23. conversion functions
  24. - the Python int <-> size_t/Py_ssize_t conversion functions expect that
  25. PyLong_SHIFT is strictly less than the number of bits in a size_t
  26. - the marshal code currently expects that PyLong_SHIFT is a multiple of 15
  27. - NSMALLNEGINTS and NSMALLPOSINTS should be small enough to fit in a single
  28. digit; with the current values this forces PyLong_SHIFT >= 9
  29. The values 15 and 30 should fit all of the above requirements, on any
  30. platform.
  31. */
  32. #if PYLONG_BITS_IN_DIGIT == 30
  33. typedef uint32_t digit;
  34. typedef int32_t sdigit; /* signed variant of digit */
  35. typedef uint64_t twodigits;
  36. typedef int64_t stwodigits; /* signed variant of twodigits */
  37. #define PyLong_SHIFT 30
  38. #define _PyLong_DECIMAL_SHIFT 9 /* max(e such that 10**e fits in a digit) */
  39. #define _PyLong_DECIMAL_BASE ((digit)1000000000) /* 10 ** DECIMAL_SHIFT */
  40. #elif PYLONG_BITS_IN_DIGIT == 15
  41. typedef unsigned short digit;
  42. typedef short sdigit; /* signed variant of digit */
  43. typedef unsigned long twodigits;
  44. typedef long stwodigits; /* signed variant of twodigits */
  45. #define PyLong_SHIFT 15
  46. #define _PyLong_DECIMAL_SHIFT 4 /* max(e such that 10**e fits in a digit) */
  47. #define _PyLong_DECIMAL_BASE ((digit)10000) /* 10 ** DECIMAL_SHIFT */
  48. #else
  49. #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
  50. #endif
  51. #define PyLong_BASE ((digit)1 << PyLong_SHIFT)
  52. #define PyLong_MASK ((digit)(PyLong_BASE - 1))
  53. #if PyLong_SHIFT % 5 != 0
  54. #error "longobject.c requires that PyLong_SHIFT be divisible by 5"
  55. #endif
  56. /* Long integer representation.
  57. The absolute value of a number is equal to
  58. SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
  59. Negative numbers are represented with ob_size < 0;
  60. zero is represented by ob_size == 0.
  61. In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
  62. digit) is never zero. Also, in all cases, for all valid i,
  63. 0 <= ob_digit[i] <= MASK.
  64. The allocation function takes care of allocating extra memory
  65. so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
  66. CAUTION: Generic code manipulating subtypes of PyVarObject has to
  67. aware that ints abuse ob_size's sign bit.
  68. */
  69. struct _longobject {
  70. PyObject_VAR_HEAD
  71. digit ob_digit[1];
  72. };
  73. PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
  74. /* Return a copy of src. */
  75. PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
  76. #ifdef __cplusplus
  77. }
  78. #endif
  79. #endif /* !Py_LONGINTREPR_H */
  80. #endif /* Py_LIMITED_API */
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