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Some minor cleanups in PyLong_FromLong: 

- fast path wasn't being properly taken for negative ints;
   thanks Victor Stinner for pointing this out.
 - use Py_SAFE_DOWNCAST instead of direct casting to digit
   (it's safer, especially if we ever consider moving to 30-bit
   digits)
 - cleaner way to write negation
This commit is contained in:
Mark Dickinson 2009-01-24 15:02:35 +00:00
parent 59e4779abc
commit d4624c3331
1 changed files with 15 additions and 12 deletions
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27
Objects/longobject.c
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@ -175,7 +175,7 @@ PyObject *
PyLong_FromLong(long ival)
{
PyLongObject *v;
unsigned long abs_ival;
unsigned long abs_ival;
unsigned long t; /* unsigned so >> doesn't propagate sign bit */
int ndigits = 0;
int sign = 1;
@ -183,33 +183,35 @@ PyLong_FromLong(long ival)
CHECK_SMALL_INT(ival);
if (ival < 0) {
/* if LONG_MIN == -LONG_MAX-1 (true on most platforms) then
ANSI C says that the result of -ival is undefined when ival
== LONG_MIN. Hence the following workaround. */
abs_ival = (unsigned long)(-1-ival) + 1;
/* negate: can't write this as abs_ival = -ival since that
invokes undefined behaviour when ival is LONG_MIN */
abs_ival = 0U-(unsigned long)ival;
sign = -1;
}
else {
abs_ival = (unsigned long)ival;
}
/* Fast path for single-digits ints */
if (!(ival>>PyLong_SHIFT)) {
/* Fast path for single-digit ints */
if (!(abs_ival >> PyLong_SHIFT)) {
v = _PyLong_New(1);
if (v) {
Py_SIZE(v) = sign;
v->ob_digit[0] = (digit)ival;
v->ob_digit[0] = Py_SAFE_DOWNCAST(
abs_ival, unsigned long, digit);
}
return (PyObject*)v;
}
/* 2 digits */
if (!(ival >> 2*PyLong_SHIFT)) {
if (!(abs_ival >> 2*PyLong_SHIFT)) {
v = _PyLong_New(2);
if (v) {
Py_SIZE(v) = 2*sign;
v->ob_digit[0] = (digit)ival & PyLong_MASK;
v->ob_digit[1] = (digit)(ival >> PyLong_SHIFT);
v->ob_digit[0] = Py_SAFE_DOWNCAST(
abs_ival & PyLong_MASK, unsigned long, digit);
v->ob_digit[1] = Py_SAFE_DOWNCAST(
abs_ival >> PyLong_SHIFT, unsigned long, digit);
}
return (PyObject*)v;
}
@ -226,7 +228,8 @@ PyLong_FromLong(long ival)
Py_SIZE(v) = ndigits*sign;
t = abs_ival;
while (t) {
*p++ = (digit)(t & PyLong_MASK);
*p++ = Py_SAFE_DOWNCAST(
t & PyLong_MASK, unsigned long, digit);
t >>= PyLong_SHIFT;
}
}