[Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison

[jay.krell at cornell.edu]

1.5.2 source:

Are those trailing Py.._From... doing heap allocations? I believe so. Yuck.
That probably dominates everything, in general, in Python. Besides, "PyLong"
is more expensive than "PyDouble", right? Well, it looks like one level of
its heap allocation is made very fast, just pluck the head of the free list.
Why does integer division return a long? I can understand integer
multiplication..

static PyObject *
float_div(v, w)
 PyFloatObject *v;
 PyFloatObject *w;
{
 double result;
 if (w->ob_fval == 0) {
  PyErr_SetString(PyExc_ZeroDivisionError, "float division");
  return NULL;
 }
 PyFPE_START_PROTECT("divide", return 0)
 result = v->ob_fval / w->ob_fval;
 PyFPE_END_PROTECT(result)
 return PyFloat_FromDouble(result);
}

static PyObject *
int_div(x, y)
 PyIntObject *x;
 PyIntObject *y;
{
 long d, m;
 if (i_divmod(x, y, &d, &m) < 0)
  return NULL;
 return PyInt_FromLong(d);
}

static int
i_divmod(x, y, p_xdivy, p_xmody)
 register PyIntObject *x, *y;
 long *p_xdivy, *p_xmody;
{
 long xi = x->ob_ival;
 long yi = y->ob_ival;
 long xdivy, xmody;

 if (yi == 0) {
  PyErr_SetString(PyExc_ZeroDivisionError,
    "integer division or modulo");
  return -1;
 }
 if (yi < 0) {
  if (xi < 0)
   xdivy = -xi / -yi;
  else
   xdivy = - (xi / -yi);
 }
 else {
  if (xi < 0)
   xdivy = - (-xi / yi);
  else
   xdivy = xi / yi;
 }
 xmody = xi - xdivy*yi;
 if ((xmody < 0 && yi > 0) || (xmody > 0 && yi < 0)) {
  xmody += yi;
  xdivy -= 1;
 }
 *p_xdivy = xdivy;
 *p_xmody = xmody;
 return 0;
}


-----Original Message-----
From: Fredrik Lundh <effbot at telia.com>
To: jay.krell at cornell.edu <jay.krell at cornell.edu>
Cc: python-list at python.org <python-list at python.org>
Date: Thursday, October 26, 2000 12:25 PM
Subject: Re: [Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich ,
comparison


>jay wrote:
>> But is integer division actually much faster than floating point
division? I
>> don't believe there is a fast algorithm for integer division.
>
>On my PII, floating point division under Python is *faster* than
>integer division (hint: look at the float_div and int_div functions,
>and you'll understand why...)
>
>(btw, my "wow" meant "wow, I've seen many strange arguments
>in this thread, but not so many in one single paragraph...")
>
></F>
>
>
>--
>http://www.python.org/mailman/listinfo/python-list