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
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@ -175,7 +175,7 @@ PyObject *
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PyLong_FromLong(long ival)
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{
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PyLongObject *v;
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unsigned long abs_ival;
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unsigned long abs_ival;
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unsigned long t; /* unsigned so >> doesn't propagate sign bit */
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int ndigits = 0;
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int sign = 1;
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@ -183,33 +183,35 @@ PyLong_FromLong(long ival)
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CHECK_SMALL_INT(ival);
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if (ival < 0) {
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/* if LONG_MIN == -LONG_MAX-1 (true on most platforms) then
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ANSI C says that the result of -ival is undefined when ival
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== LONG_MIN. Hence the following workaround. */
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abs_ival = (unsigned long)(-1-ival) + 1;
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/* negate: can't write this as abs_ival = -ival since that
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invokes undefined behaviour when ival is LONG_MIN */
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abs_ival = 0U-(unsigned long)ival;
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sign = -1;
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}
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else {
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abs_ival = (unsigned long)ival;
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}
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/* Fast path for single-digits ints */
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if (!(ival>>PyLong_SHIFT)) {
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/* Fast path for single-digit ints */
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if (!(abs_ival >> PyLong_SHIFT)) {
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v = _PyLong_New(1);
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if (v) {
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Py_SIZE(v) = sign;
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v->ob_digit[0] = (digit)ival;
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v->ob_digit[0] = Py_SAFE_DOWNCAST(
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abs_ival, unsigned long, digit);
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}
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return (PyObject*)v;
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}
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/* 2 digits */
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if (!(ival >> 2*PyLong_SHIFT)) {
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if (!(abs_ival >> 2*PyLong_SHIFT)) {
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v = _PyLong_New(2);
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if (v) {
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Py_SIZE(v) = 2*sign;
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v->ob_digit[0] = (digit)ival & PyLong_MASK;
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v->ob_digit[1] = (digit)(ival >> PyLong_SHIFT);
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v->ob_digit[0] = Py_SAFE_DOWNCAST(
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abs_ival & PyLong_MASK, unsigned long, digit);
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v->ob_digit[1] = Py_SAFE_DOWNCAST(
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abs_ival >> PyLong_SHIFT, unsigned long, digit);
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}
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return (PyObject*)v;
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}
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@ -226,7 +228,8 @@ PyLong_FromLong(long ival)
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Py_SIZE(v) = ndigits*sign;
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t = abs_ival;
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while (t) {
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*p++ = (digit)(t & PyLong_MASK);
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*p++ = Py_SAFE_DOWNCAST(
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t & PyLong_MASK, unsigned long, digit);
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t >>= PyLong_SHIFT;
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}
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}
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