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Change long/long true division to return as many good bits as it can;

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e.g., (1L << 40000)/(1L << 40001) returns 0.5, not Inf or NaN or whatever.
This commit is contained in:
Tim Peters 2001-09-04 06:17:36 +00:00
parent 9c1d7fd5f2
commit e2a600099d
3 changed files with 78 additions and 2 deletions
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33
Objects/longobject.c
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@ -1584,7 +1584,38 @@ long_classic_div(PyObject *v, PyObject *w)
static PyObject *
long_true_divide(PyObject *v, PyObject *w)
{
return PyFloat_Type.tp_as_number->nb_divide(v, w);
PyLongObject *a, *b;
double ad, bd;
int aexp, bexp;
CONVERT_BINOP(v, w, &a, &b);
ad = _PyLong_AsScaledDouble((PyObject *)a, &aexp);
bd = _PyLong_AsScaledDouble((PyObject *)b, &bexp);
if ((ad == -1.0 || bd == -1.0) && PyErr_Occurred())
return NULL;
if (bd == 0.0) {
PyErr_SetString(PyExc_ZeroDivisionError,
"long division or modulo by zero");
return NULL;
}
/* True value is very close to ad/bd * 2**(SHIFT*(aexp-bexp)) */
ad /= bd; /* overflow/underflow impossible here */
aexp -= bexp;
if (aexp > INT_MAX / SHIFT)
goto overflow;
errno = 0;
ad = ldexp(ad, aexp * SHIFT);
if (ad != 0 && errno == ERANGE) /* ignore underflow to 0.0 */
goto overflow;
return PyFloat_FromDouble(ad);
overflow:
PyErr_SetString(PyExc_OverflowError,
"long/long too large for a float");
return NULL;
}
static PyObject *