New submission from Farhan Sajjad <sajja...@outlook.com>:
Found this rather obscure behavior where certain 64 bit numbers are changing
(probably losing precision somewhere down the call chain) if converted from
PyLong to double using the PyLong_AsDouble C API function.
TO REPRODUCE:
#define __SIZEOF_STRS__ 512
static PyObject*
test_pylong(PyObject* self, PyObject* args)
{
char rBuffer[__SIZEOF_STRS__];
char* strValue;
if (!PyArg_ParseTuple(args, "s", &strValue))
return NULL;
{
printf("%s AS INGRESS\n", strValue);
double dblValue = PyLong_AsDouble(
PyLong_FromString(strValue, NULL, 10));
snprintf(rBuffer, __SIZEOF_STRS__, "%.0f",
PyLong_AsDouble(PyLong_FromString(strValue, NULL, 10)));
printf("CONVERT 1: %.0f\nCONVERT 2: %s\n", dblValue, rBuffer);
}
Py_RETURN_NONE;
}
Test:
>>> test_pylong("1639873214337061279")
1639873214337061279 AS INGRESS
CONVERT 1: 1639873214337061376
CONVERT 2: 1639873214337061376
----------
messages: 342619
nosy: sajjadfx
priority: normal
severity: normal
status: open
title: C API Function PyLong_AsDouble Returning Wrong Value
type: behavior
versions: Python 3.7
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36934>
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