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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.
This commit is contained in:
Mark Dickinson 2008-07-30 12:01:41 +00:00
parent efdf706a9f
commit abe0aee3cf
1 changed files with 54 additions and 38 deletions
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92
Modules/mathmodule.c
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@ -414,6 +414,7 @@ math_sum(PyObject *self, PyObject *seq)
PyObject *item, *iter, *sum = NULL; PyObject *item, *iter, *sum = NULL;
Py_ssize_t i, j, n = 0, m = NUM_PARTIALS; Py_ssize_t i, j, n = 0, m = NUM_PARTIALS;
double x, y, t, ps[NUM_PARTIALS], *p = ps; double x, y, t, ps[NUM_PARTIALS], *p = ps;
double xsave, special_sum = 0.0, inf_sum = 0.0;
volatile double hi, yr, lo; volatile double hi, yr, lo;
iter = PyObject_GetIter(seq); iter = PyObject_GetIter(seq);
@ -438,10 +439,11 @@ math_sum(PyObject *self, PyObject *seq)
if (PyErr_Occurred()) if (PyErr_Occurred())
goto _sum_error; goto _sum_error;
xsave = x;
for (i = j = 0; j < n; j++) { /* for y in partials */ for (i = j = 0; j < n; j++) { /* for y in partials */
y = p[j]; y = p[j];
if (fabs(x) < fabs(y)) { if (fabs(x) < fabs(y)) {
t = x; x = y; y = t; t = x; x = y; y = t;
} }
hi = x + y; hi = x + y;
yr = hi - x; yr = hi - x;
@ -450,54 +452,68 @@ math_sum(PyObject *self, PyObject *seq)
p[i++] = lo; p[i++] = lo;
x = hi; x = hi;
} }
n = i; /* ps[i:] = [x] */ n = i; /* ps[i:] = [x] */
if (x != 0.0) { if (x != 0.0) {
/* If non-finite, reset partials, effectively if (! Py_IS_FINITE(x)) {
adding subsequent items without roundoff /* a nonfinite x could arise either as
and yielding correct non-finite results, a result of intermediate overflow, or
provided IEEE 754 rules are observed */ as a result of a nan or inf in the
if (! Py_IS_FINITE(x)) summands */
if (Py_IS_FINITE(xsave)) {
PyErr_SetString(PyExc_OverflowError,
"intermediate overflow in sum");
goto _sum_error;
}
if (Py_IS_INFINITY(xsave))
inf_sum += xsave;
special_sum += xsave;
/* reset partials */
n = 0; n = 0;
}
else if (n >= m && _sum_realloc(&p, n, ps, &m)) else if (n >= m && _sum_realloc(&p, n, ps, &m))
goto _sum_error; goto _sum_error;
p[n++] = x; else
p[n++] = x;
} }
} }
if (special_sum != 0.0) {
if (Py_IS_NAN(inf_sum))
PyErr_SetString(PyExc_ValueError,
"-inf + inf in sum");
else
sum = PyFloat_FromDouble(special_sum);
goto _sum_error;
}
hi = 0.0; hi = 0.0;
if (n > 0) { if (n > 0) {
hi = p[--n]; hi = p[--n];
if (Py_IS_FINITE(hi)) { /* sum_exact(ps, hi) from the top, stop when the sum becomes
/* sum_exact(ps, hi) from the top, stop when the sum becomes inexact. */ inexact. */
while (n > 0) { while (n > 0) {
x = hi; x = hi;
y = p[--n]; y = p[--n];
assert(fabs(y) < fabs(x)); assert(fabs(y) < fabs(x));
hi = x + y; hi = x + y;
yr = hi - x; yr = hi - x;
lo = y - yr; lo = y - yr;
if (lo != 0.0) if (lo != 0.0)
break; break;
}
/* Make half-even rounding work across multiple partials. Needed
so that sum([1e-16, 1, 1e16]) will round-up the last digit to
two instead of down to zero (the 1e-16 makes the 1 slightly
closer to two). With a potential 1 ULP rounding error fixed-up,
math.sum() can guarantee commutativity. */
if (n > 0 && ((lo < 0.0 && p[n-1] < 0.0) ||
(lo > 0.0 && p[n-1] > 0.0))) {
y = lo * 2.0;
x = hi + y;
yr = x - hi;
if (y == yr)
hi = x;
}
} }
else { /* raise exception corresponding to a special value */ /* Make half-even rounding work across multiple partials.
errno = Py_IS_NAN(hi) ? EDOM : ERANGE; Needed so that sum([1e-16, 1, 1e16]) will round-up the last
if (is_error(hi)) digit to two instead of down to zero (the 1e-16 makes the 1
goto _sum_error; slightly closer to two). With a potential 1 ULP rounding
error fixed-up, math.sum() can guarantee commutativity. */
if (n > 0 && ((lo < 0.0 && p[n-1] < 0.0) ||
(lo > 0.0 && p[n-1] > 0.0))) {
y = lo * 2.0;
x = hi + y;
yr = x - hi;
if (y == yr)
hi = x;
} }
} }
sum = PyFloat_FromDouble(hi); sum = PyFloat_FromDouble(hi);