[issue4258] Use 30-bit digits instead of 15-bit digits for Python integers.

Include/longintrepr.h

 #ifndef Py_LONGINTREPR_H
 #define Py_LONGINTREPR_H
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 
 /* This is published for the benefit of "friend" marshal.c only. */
 
 /* Parameters of the long integer representation.
    These shouldn't have to be changed as C should guarantee that a short
    contains at least 16 bits, but it's made changeable anyway.
    Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits'
    should be able to hold the intermediate results in 'mul'
    (at most (BASE-1)*(2*BASE+1) == MASK*(2*MASK+3)).
    Also, x_sub assumes that 'digit' is an unsigned type, and overflow
    is handled by taking the result mod 2**N for some N > SHIFT.
    And, at some places it is assumed that MASK fits in an int, as well.
    long_pow() requires that SHIFT be divisible by 5. */
 
+/* Additional restrictions: PyLong_SHIFT should be greater than or equal to 8,
+   and strictly less than the number of bits in an unsigned long.  It should
+   also be strictly less than the number of bits in a Py_ssize_t.
+   Furthermore, NSMALLNEGINTS and NSMALLPOSINTS should fit in a digit. */

[Martin v. Löwis, 2009/02/17 22:39:18]

Merge the comments into a single on. There is no need to preserve the evolution
of the code in the comment structure.

[dickinsm, 2009/02/18 17:06:33]

Done, along with a general rewrite of this set of comments.

+
+
+#if HAVE_STDINT_H
+#include <stdint.h>
+#endif
+
+#if PYLONG_DIGIT_SIZE == 30
+#if !(defined HAVE_UINT64_T && defined HAVE_UINT32_T &&          \
+      defined HAVE_INT64_T && defined HAVE_INT32_T)
+#error "30-bit long digits requested, but the necessary types are not available on this platform"
+#endif
+typedef PY_UINT32_T digit;
+typedef PY_INT32_T sdigit; /* signed variant of digit */
+typedef PY_UINT64_T twodigits;
+typedef PY_INT64_T stwodigits; /* signed variant of twodigits */
+#define PyLong_SHIFT    30
+#elif PYLONG_DIGIT_SIZE == 15
 typedef unsigned short digit;
-typedef short sdigit;                   /* signed variant of digit */
-#define BASE_TWODIGITS_TYPE long
-typedef unsigned BASE_TWODIGITS_TYPE twodigits;
-typedef BASE_TWODIGITS_TYPE stwodigits; /* signed variant of twodigits */
-
+typedef short sdigit; /* signed variant of digit */
+typedef unsigned long twodigits;
+typedef long stwodigits; /* signed variant of twodigits */
 #define PyLong_SHIFT    15
+#else
+#error "PYLONG_DIGIT_SIZE should be 15 or 30"
+#endif
 #define PyLong_BASE     ((digit)1 << PyLong_SHIFT)
 #define PyLong_MASK     ((digit)(PyLong_BASE - 1))
 
 #if PyLong_SHIFT % 5 != 0
 #error "longobject.c requires that SHIFT be divisible by 5"
 #endif
 
 /* Long integer representation.
    The absolute value of a number is equal to
         SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
@@ skipping 16 matching lines @@
 
 PyAPI_FUNC(PyLongObject *) _PyLong_New(Py_ssize_t);
 
 /* Return a copy of src. */
 PyAPI_FUNC(PyObject *) _PyLong_Copy(PyLongObject *src);
 
 #ifdef __cplusplus
 }
 #endif
 #endif /* !Py_LONGINTREPR_H */