Issue #4258: Make it possible to use 30-bit digits for PyLongs:
- new configure option --enable-big-digits
- new structseq sys.int_info giving information about the internal format
By default, 30-bit digits are enabled on 64-bit machines but
disabled on 32-bit machines.
diff --git a/Objects/longobject.c b/Objects/longobject.c
index b758c40..e1df9d9 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -4,6 +4,7 @@
#include "Python.h"
#include "longintrepr.h"
+#include "structseq.h"
#include <ctype.h>
#include <stddef.h>
@@ -204,6 +205,7 @@
return (PyObject*)v;
}
+#if PyLONG_SHIFT==15
/* 2 digits */
if (!(abs_ival >> 2*PyLong_SHIFT)) {
v = _PyLong_New(2);
@@ -216,6 +218,7 @@
}
return (PyObject*)v;
}
+#endif
/* Larger numbers: loop to determine number of digits */
t = abs_ival;
@@ -2864,10 +2867,20 @@
CHECK_BINOP(a, b);
+ /* fast path for single-digit multiplication */
if (ABS(Py_SIZE(a)) <= 1 && ABS(Py_SIZE(b)) <= 1) {
- PyObject *r;
- r = PyLong_FromLong(MEDIUM_VALUE(a)*MEDIUM_VALUE(b));
- return r;
+ stwodigits v = (stwodigits)(MEDIUM_VALUE(a)) * MEDIUM_VALUE(b);
+#ifdef HAVE_LONG_LONG
+ return PyLong_FromLongLong((PY_LONG_LONG)v);
+#else
+ /* if we don't have long long then we're almost certainly
+ using 15-bit digits, so v will fit in a long. In the
+ unlikely event that we're using 30-bit digits on a platform
+ without long long, a large v will just cause us to fall
+ through to the general multiplication code below. */
+ if (v >= LONG_MIN && v <= LONG_MAX)
+ return PyLong_FromLong((long)v);
+#endif
}
z = k_mul(a, b);
@@ -3991,6 +4004,45 @@
PyObject_Del, /* tp_free */
};
+static PyTypeObject Int_InfoType;
+
+PyDoc_STRVAR(int_info__doc__,
+"sys.int_info\n\
+\n\
+A struct sequence that holds information about Python's\n\
+internal representation of integers. The attributes are read only.");
+
+static PyStructSequence_Field int_info_fields[] = {
+ {"bits_per_digit", "size of a digit in bits"},
+ {"sizeof_digit", "size in bytes of the C type used to "
+ "represent a digit"},
+ {NULL, NULL}
+};
+
+static PyStructSequence_Desc int_info_desc = {
+ "sys.int_info", /* name */
+ int_info__doc__, /* doc */
+ int_info_fields, /* fields */
+ 2 /* number of fields */
+};
+
+PyObject *
+PyLong_GetInfo(void)
+{
+ PyObject* int_info;
+ int field = 0;
+ int_info = PyStructSequence_New(&Int_InfoType);
+ if (int_info == NULL)
+ return NULL;
+ PyStructSequence_SET_ITEM(int_info, field++, PyLong_FromLong(PyLong_SHIFT));
+ PyStructSequence_SET_ITEM(int_info, field++, PyLong_FromLong(sizeof(digit)));
+ if (PyErr_Occurred()) {
+ Py_CLEAR(int_info);
+ return NULL;
+ }
+ return int_info;
+}
+
int
_PyLong_Init(void)
{
@@ -4023,6 +4075,10 @@
v->ob_digit[0] = abs(ival);
}
#endif
+ /* initialize int_info */
+ if (Int_InfoType.tp_name == 0)
+ PyStructSequence_InitType(&Int_InfoType, &int_info_desc);
+
return 1;
}