Fix special-value handling for math.sum.
Also minor cleanups to the code: fix tabbing, remove trailing whitespace, and reformat to fit into 80 columns.
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@ -414,6 +414,7 @@ math_sum(PyObject *self, PyObject *seq)
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PyObject *item, *iter, *sum = NULL;
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Py_ssize_t i, j, n = 0, m = NUM_PARTIALS;
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double x, y, t, ps[NUM_PARTIALS], *p = ps;
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double xsave, special_sum = 0.0, inf_sum = 0.0;
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volatile double hi, yr, lo;
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iter = PyObject_GetIter(seq);
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@ -438,10 +439,11 @@ math_sum(PyObject *self, PyObject *seq)
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if (PyErr_Occurred())
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goto _sum_error;
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xsave = x;
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for (i = j = 0; j < n; j++) { /* for y in partials */
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y = p[j];
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if (fabs(x) < fabs(y)) {
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t = x; x = y; y = t;
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t = x; x = y; y = t;
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}
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hi = x + y;
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yr = hi - x;
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@ -450,54 +452,68 @@ math_sum(PyObject *self, PyObject *seq)
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p[i++] = lo;
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x = hi;
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}
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n = i; /* ps[i:] = [x] */
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n = i; /* ps[i:] = [x] */
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if (x != 0.0) {
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/* If non-finite, reset partials, effectively
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adding subsequent items without roundoff
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and yielding correct non-finite results,
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provided IEEE 754 rules are observed */
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if (! Py_IS_FINITE(x))
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if (! Py_IS_FINITE(x)) {
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/* a nonfinite x could arise either as
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a result of intermediate overflow, or
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as a result of a nan or inf in the
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summands */
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if (Py_IS_FINITE(xsave)) {
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PyErr_SetString(PyExc_OverflowError,
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"intermediate overflow in sum");
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goto _sum_error;
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}
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if (Py_IS_INFINITY(xsave))
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inf_sum += xsave;
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special_sum += xsave;
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/* reset partials */
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n = 0;
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}
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else if (n >= m && _sum_realloc(&p, n, ps, &m))
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goto _sum_error;
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p[n++] = x;
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else
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p[n++] = x;
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}
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}
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if (special_sum != 0.0) {
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if (Py_IS_NAN(inf_sum))
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PyErr_SetString(PyExc_ValueError,
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"-inf + inf in sum");
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else
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sum = PyFloat_FromDouble(special_sum);
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goto _sum_error;
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}
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hi = 0.0;
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if (n > 0) {
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hi = p[--n];
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if (Py_IS_FINITE(hi)) {
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/* sum_exact(ps, hi) from the top, stop when the sum becomes inexact. */
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while (n > 0) {
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x = hi;
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y = p[--n];
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assert(fabs(y) < fabs(x));
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hi = x + y;
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yr = hi - x;
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lo = y - yr;
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if (lo != 0.0)
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break;
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}
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/* Make half-even rounding work across multiple partials. Needed
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so that sum([1e-16, 1, 1e16]) will round-up the last digit to
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two instead of down to zero (the 1e-16 makes the 1 slightly
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closer to two). With a potential 1 ULP rounding error fixed-up,
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math.sum() can guarantee commutativity. */
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if (n > 0 && ((lo < 0.0 && p[n-1] < 0.0) ||
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(lo > 0.0 && p[n-1] > 0.0))) {
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y = lo * 2.0;
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x = hi + y;
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yr = x - hi;
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if (y == yr)
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hi = x;
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}
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/* sum_exact(ps, hi) from the top, stop when the sum becomes
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inexact. */
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while (n > 0) {
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x = hi;
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y = p[--n];
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assert(fabs(y) < fabs(x));
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hi = x + y;
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yr = hi - x;
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lo = y - yr;
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if (lo != 0.0)
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break;
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}
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else { /* raise exception corresponding to a special value */
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errno = Py_IS_NAN(hi) ? EDOM : ERANGE;
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if (is_error(hi))
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goto _sum_error;
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/* Make half-even rounding work across multiple partials.
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Needed so that sum([1e-16, 1, 1e16]) will round-up the last
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digit to two instead of down to zero (the 1e-16 makes the 1
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slightly closer to two). With a potential 1 ULP rounding
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error fixed-up, math.sum() can guarantee commutativity. */
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if (n > 0 && ((lo < 0.0 && p[n-1] < 0.0) ||
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(lo > 0.0 && p[n-1] > 0.0))) {
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y = lo * 2.0;
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x = hi + y;
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yr = x - hi;
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if (y == yr)
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hi = x;
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}
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}
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sum = PyFloat_FromDouble(hi);
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