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authorRaymond Hettinger <python@rcn.com>2008-06-09 11:24:47 (GMT)
committerRaymond Hettinger <python@rcn.com>2008-06-09 11:24:47 (GMT)
commitd62341414109ff16d6477e370e380c6dec9db9d6 (patch)
tree67b4e8638067359d7e37ba1cf3aa2d13c277ed93 /Modules/mathmodule.c
parent7b1ed66372a26591c07f4c97e20c3c58acefa306 (diff)
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Unhappy buildbots. Revert 64052. Long doubles have unexpected effects on some builds.
Diffstat (limited to 'Modules/mathmodule.c')
-rw-r--r--Modules/mathmodule.c44
1 files changed, 24 insertions, 20 deletions
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 16d91e9..32c2400 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -324,12 +324,17 @@ FUNC1(tanh, tanh, 0,
Note 3: The itermediate values lo, yr, and hi are declared volatile so
aggressive compilers won't algebraicly reduce lo to always be exactly 0.0.
-
- Note 4: Intermediate values and partial sums are declared as long doubles
- as a way to eliminate double rounding environments where the operations
- are carried-out in extended precision but stored in double precision
- variables. In some cases, this doesn't help because the compiler
- treats long doubles as doubles (i.e. the MS compiler for Win32 builds).
+ Also, the volatile declaration forces the values to be stored in memory as
+ regular doubles instead of extended long precision (80-bit) values. This
+ prevents double rounding because any addition or substraction of two doubles
+ can be resolved exactly into double-sized hi and lo values. As long as the
+ hi value gets forced into a double before yr and lo are computed, the extra
+ bits in downstream extended precision operations (x87 for example) will be
+ exactly zero and therefore can be losslessly stored back into a double,
+ thereby preventing double rounding.
+
+ Note 4: A similar implementation is in Modules/cmathmodule.c.
+ Be sure to update both when making changes.
Note 5: The signature of math.sum() differs from __builtin__.sum()
because the start argument doesn't make sense in the context of
@@ -342,28 +347,28 @@ FUNC1(tanh, tanh, 0,
/* Extend the partials array p[] by doubling its size. */
static int /* non-zero on error */
-_sum_realloc(long double **p_ptr, Py_ssize_t n,
- long double *ps, Py_ssize_t *m_ptr)
+_sum_realloc(double **p_ptr, Py_ssize_t n,
+ double *ps, Py_ssize_t *m_ptr)
{
void *v = NULL;
Py_ssize_t m = *m_ptr;
- m += m; /* long double */
- if (n < m && m < (PY_SSIZE_T_MAX / sizeof(long double))) {
- long double *p = *p_ptr;
+ m += m; /* double */
+ if (n < m && m < (PY_SSIZE_T_MAX / sizeof(double))) {
+ double *p = *p_ptr;
if (p == ps) {
- v = PyMem_Malloc(sizeof(long double) * m);
+ v = PyMem_Malloc(sizeof(double) * m);
if (v != NULL)
- memcpy(v, ps, sizeof(long double) * n);
+ memcpy(v, ps, sizeof(double) * n);
}
else
- v = PyMem_Realloc(p, sizeof(long double) * m);
+ v = PyMem_Realloc(p, sizeof(double) * m);
}
if (v == NULL) { /* size overflow or no memory */
PyErr_SetString(PyExc_MemoryError, "math sum partials");
return 1;
}
- *p_ptr = (long double*) v;
+ *p_ptr = (double*) v;
*m_ptr = m;
return 0;
}
@@ -403,8 +408,8 @@ math_sum(PyObject *self, PyObject *seq)
{
PyObject *item, *iter, *sum = NULL;
Py_ssize_t i, j, n = 0, m = NUM_PARTIALS;
- long double x, y, t, ps[NUM_PARTIALS], *p = ps;
- volatile long double hi, yr, lo;
+ double x, y, t, ps[NUM_PARTIALS], *p = ps;
+ volatile double hi, yr, lo;
iter = PyObject_GetIter(seq);
if (iter == NULL)
@@ -423,7 +428,7 @@ math_sum(PyObject *self, PyObject *seq)
goto _sum_error;
break;
}
- x = (long double)PyFloat_AsDouble(item);
+ x = PyFloat_AsDouble(item);
Py_DECREF(item);
if (PyErr_Occurred())
goto _sum_error;
@@ -490,7 +495,7 @@ math_sum(PyObject *self, PyObject *seq)
goto _sum_error;
}
}
- sum = PyFloat_FromDouble((double)hi);
+ sum = PyFloat_FromDouble(hi);
_sum_error:
PyFPE_END_PROTECT(hi)
@@ -507,7 +512,6 @@ PyDoc_STRVAR(math_sum_doc,
Return an accurate floating point sum of values in the iterable.\n\
Assumes IEEE-754 floating point arithmetic.");
-
static PyObject *
math_factorial(PyObject *self, PyObject *arg)
{