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Issue #3439: add bit_length method to int and long.

Browse source 
Thanks Fredrik Johansson and Victor Stinner for code,
Raymond Hettinger for review.
This commit is contained in:
Mark Dickinson 2008-12-17 16:14:37 +00:00
parent d0c3515bc5
commit 1a707981c8
8 changed files with 239 additions and 1 deletions
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36
Objects/intobject.c
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@ -1138,6 +1138,40 @@ int__format__(PyObject *self, PyObject *args)
return NULL;
}
static const unsigned char BitLengthTable[32] = {
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5
};
static PyObject *
int_bit_length(PyIntObject *v)
{
unsigned long n;
long r = 0;
if (v->ob_ival < 0)
/* avoid undefined behaviour when v->ob_ival == -LONG_MAX-1 */
n = 0U-(unsigned long)v->ob_ival;
else
n = (unsigned long)v->ob_ival;
while (n >= 32) {
r += 6;
n >>= 6;
}
r += (long)(BitLengthTable[n]);
return PyInt_FromLong(r);
}
PyDoc_STRVAR(int_bit_length_doc,
"int.bit_length() -> int\n\
\n\
Number of bits necessary to represent self in binary.\n\
>>> bin(37)\n\
'0b100101'\n\
>>> (37).bit_length()\n\
6");
#if 0
static PyObject *
int_is_finite(PyObject *v)
@ -1149,6 +1183,8 @@ int_is_finite(PyObject *v)
static PyMethodDef int_methods[] = {
{"conjugate", (PyCFunction)int_int, METH_NOARGS,
"Returns self, the complex conjugate of any int."},
{"bit_length", (PyCFunction)int_bit_length, METH_NOARGS,
int_bit_length_doc},
#if 0
{"is_finite", (PyCFunction)int_is_finite, METH_NOARGS,
"Returns always True."},