diff options
Diffstat (limited to 'Modules')
| -rw-r--r-- | Modules/mathmodule.c | 68 |
1 files changed, 64 insertions, 4 deletions
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c index f715418..eef8b78 100644 --- a/Modules/mathmodule.c +++ b/Modules/mathmodule.c @@ -1,6 +1,7 @@ /* Math module -- standard C math library functions, pi and e */ #include "Python.h" +#include "longintrepr.h" #ifndef _MSC_VER #ifndef __STDC__ @@ -136,10 +137,6 @@ FUNC2(fmod, fmod, " x % y may differ.") FUNC2(hypot, hypot, "hypot(x,y)\n\nReturn the Euclidean distance, sqrt(x*x + y*y).") -FUNC1(log, log, - "log(x)\n\nReturn the natural logarithm of x.") -FUNC1(log10, log10, - "log10(x)\n\nReturn the base-10 logarithm of x.") #ifdef MPW_3_1 /* This hack is needed for MPW 3.1 but not for 3.2 ... */ FUNC2(pow, power, "pow(x,y)\n\nReturn x**y (x to the power of y).") @@ -231,6 +228,69 @@ static char math_modf_doc [] = "Return the fractional and integer parts of x. Both results carry the sign\n" "of x. The integer part is returned as a real."; +/* 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 + small enough to fit in an IEEE single. log and log10 are even smaller. +*/ + +static PyObject* +loghelper(PyObject* args, double (*func)(double), char *name) +{ + PyObject *arg; + char format[16]; + + /* See whether this is a long. */ + format[0] = 'O'; + format[1] = ':'; + strcpy(format + 2, name); + if (! PyArg_ParseTuple(args, format, &arg)) + return NULL; + + /* If it is long, do it ourselves. */ + if (PyLong_Check(arg)) { + double x; + int e; + x = _PyLong_AsScaledDouble(arg, &e); + if (x <= 0.0) { + PyErr_SetString(PyExc_ValueError, + "math domain error"); + return NULL; + } + /* Value is ~= x * 2**(e*SHIFT), so the log ~= + log(x) + log(2) * e * SHIFT. + CAUTION: e*SHIFT may overflow using int arithmetic, + so force use of double. */ + x = func(x) + func(2.0) * (double)e * (double)SHIFT; + return PyFloat_FromDouble(x); + } + + /* Else let libm handle it by itself. */ + format[0] = 'd'; + return math_1(args, func, format); +} + +static PyObject * +math_log(PyObject *self, PyObject *args) +{ + return loghelper(args, log, "log"); +} + +static char math_log_doc[] = +"log(x) -> the natural logarithm (base e) of x."; + +static PyObject * +math_log10(PyObject *self, PyObject *args) +{ + return loghelper(args, log10, "log10"); +} + +static char math_log10_doc[] = +"log10(x) -> the base 10 logarithm of x."; + + static PyMethodDef math_methods[] = { {"acos", math_acos, METH_VARARGS, math_acos_doc}, {"asin", math_asin, METH_VARARGS, math_asin_doc}, |