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47e52ee0c5
This checkin is adapted from part 2 (of 3) of Trevor Perrin's patch set.
BACKWARD INCOMPATIBILITY: SHIFT must now be divisible by 5. AFAIK,
nobody will care. long_pow() could be complicated to worm around that,
if necessary.
long_pow():
- BUGFIX: This leaked the base and power when the power was negative
(and so the computation delegated to float pow).
- Instead of doing right-to-left exponentiation, do left-to-right. This
is more efficient for small bases, which is the common case.
- In addition, if the exponent is large (more than FIVEARY_CUTOFF
digits), precompute [a**i % c for i in range(32)], and go left to
right 5 bits at a time.
l_divmod():
- The signature changed so that callers who don't want the quotient,
or don't want the remainder, can pass NULL in the slot they don't
want. This saves them from having to declare a vrbl for unwanted
stuff, and remembering to decref it.
long_mod(), long_div(), long_classic_div():
- Adjust to new l_divmod() signature, and simplified as a result.
64 lines
2.1 KiB
C
64 lines
2.1 KiB
C
#ifndef Py_LONGINTREPR_H
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#define Py_LONGINTREPR_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* This is published for the benefit of "friend" marshal.c only. */
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/* Parameters of the long integer representation.
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These shouldn't have to be changed as C should guarantee that a short
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contains at least 16 bits, but it's made changeable anyway.
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Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits'
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should be able to hold the intermediate results in 'mul'
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(at most (BASE-1)*(2*BASE+1) == MASK*(2*MASK+3)).
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Also, x_sub assumes that 'digit' is an unsigned type, and overflow
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is handled by taking the result mod 2**N for some N > SHIFT.
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And, at some places it is assumed that MASK fits in an int, as well.
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long_pow() requires that SHIFT be divisible by 5. */
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typedef unsigned short digit;
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typedef unsigned int wdigit; /* digit widened to parameter size */
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#define BASE_TWODIGITS_TYPE long
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typedef unsigned BASE_TWODIGITS_TYPE twodigits;
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typedef BASE_TWODIGITS_TYPE stwodigits; /* signed variant of twodigits */
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#define SHIFT 15
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#define BASE ((digit)1 << SHIFT)
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#define MASK ((int)(BASE - 1))
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#if SHIFT % 5 != 0
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#error "longobject.c requires that SHIFT be divisible by 5"
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#endif
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/* Long integer representation.
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The absolute value of a number is equal to
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SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
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Negative numbers are represented with ob_size < 0;
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zero is represented by ob_size == 0.
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In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
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digit) is never zero. Also, in all cases, for all valid i,
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0 <= ob_digit[i] <= MASK.
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The allocation function takes care of allocating extra memory
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so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
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CAUTION: Generic code manipulating subtypes of PyVarObject has to
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aware that longs abuse ob_size's sign bit.
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*/
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struct _longobject {
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PyObject_VAR_HEAD
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digit ob_digit[1];
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};
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PyAPI_FUNC(PyLongObject *) _PyLong_New(int);
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/* Return a copy of src. */
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PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
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#ifdef __cplusplus
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}
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#endif
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#endif /* !Py_LONGINTREPR_H */
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