diff options
Diffstat (limited to 'Modules/mathmodule.c')
| -rw-r--r-- | Modules/mathmodule.c | 27 |
1 files changed, 15 insertions, 12 deletions
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c index 6eb9e91..849f7f0 100644 --- a/Modules/mathmodule.c +++ b/Modules/mathmodule.c @@ -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 */ @@ -1269,11 +1268,12 @@ 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) @@ -1281,18 +1281,21 @@ 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); } |