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  r77234 | mark.dickinson | 2010-01-02 14:45:40 +0000 (Sat, 02 Jan 2010) | 7 lines

  Refactor some longobject internals:  PyLong_AsDouble and _PyLong_AsScaledDouble
  (the latter renamed to _PyLong_Frexp) now use the same core code.  The
  exponent produced by _PyLong_Frexp now has type Py_ssize_t instead of the
  previously used int, and no longer needs scaling by PyLong_SHIFT.  This
  frees the math module from having to know anything about the PyLong
  implementation.  This closes issue #5576.
........
This commit is contained in:
Mark Dickinson 2010-01-02 15:33:56 +00:00
parent 01f748a832
commit 6ecd9e53ce
3 changed files with 168 additions and 240 deletions
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27
Modules/mathmodule.c
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@ -54,7 +54,6 @@ raised for division by zero and mod by zero.
#include "Python.h"
#include "_math.h"
#include "longintrepr.h" /* just for SHIFT */
#ifdef _OSF_SOURCE
/* OSF1 5.1 doesn't make this available with XOPEN_SOURCE_EXTENDED defined */
@ -1342,11 +1341,12 @@ PyDoc_STRVAR(math_modf_doc,
/* A decent logarithm is easy to compute even for huge longs, but libm can't
do that by itself -- loghelper can. func is log or log10, and name is
"log" or "log10". Note that overflow isn't possible: a long can contain
no more than INT_MAX * SHIFT bits, so has value certainly less than
2**(2**64 * 2**16) == 2**2**80, and log2 of that is 2**80, which is
"log" or "log10". Note that overflow of the result isn't possible: a long
can contain no more than INT_MAX * SHIFT bits, so has value certainly less
than 2**(2**64 * 2**16) == 2**2**80, and log2 of that is 2**80, which is
small enough to fit in an IEEE single. log and log10 are even smaller.
*/
However, intermediate overflow is possible for a long if the number of bits
in that long is larger than PY_SSIZE_T_MAX. */
static PyObject*
loghelper(PyObject* arg, double (*func)(double), char *funcname)
@ -1354,18 +1354,21 @@ loghelper(PyObject* arg, double (*func)(double), char *funcname)
/* If it is long, do it ourselves. */
if (PyLong_Check(arg)) {
double x;
int e;
x = _PyLong_AsScaledDouble(arg, &e);
Py_ssize_t e;
x = _PyLong_Frexp((PyLongObject *)arg, &e);
if (x == -1.0 && PyErr_Occurred())
return NULL;
if (x <= 0.0) {
PyErr_SetString(PyExc_ValueError,
"math domain error");
return NULL;
}
/* Value is ~= x * 2**(e*PyLong_SHIFT), so the log ~=
log(x) + log(2) * e * PyLong_SHIFT.
CAUTION: e*PyLong_SHIFT may overflow using int arithmetic,
so force use of double. */
x = func(x) + (e * (double)PyLong_SHIFT) * func(2.0);
/* Special case for log(1), to make sure we get an
exact result there. */
if (e == 1 && x == 0.5)
return PyFloat_FromDouble(0.0);
/* Value is ~= x * 2**e, so the log ~= log(x) + log(2) * e. */
x = func(x) + func(2.0) * e;
return PyFloat_FromDouble(x);
}