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GH-100485: Convert from Fast2Sum to 2Sum (GH-100836)

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Raymond Hettinger 2023-01-07 21:37:08 -06:00 committed by GitHub
parent 951303fd85
commit df3851fe4a
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1 changed files with 16 additions and 13 deletions
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29
Modules/mathmodule.c
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@ -2847,7 +2847,7 @@ based on ideas from three sources:
The double length routines allow for quite a bit of instruction The double length routines allow for quite a bit of instruction
level parallelism. On a 3.22 Ghz Apple M1 Max, the incremental level parallelism. On a 3.22 Ghz Apple M1 Max, the incremental
cost of increasing the input vector size by one is 6.25 nsec. cost of increasing the input vector size by one is 6.0 nsec.
dl_zero() returns an extended precision zero dl_zero() returns an extended precision zero
dl_split() exactly splits a double into two half precision components. dl_split() exactly splits a double into two half precision components.
@ -2860,22 +2860,25 @@ dl_to_d() converts from extended precision to double precision.
typedef struct{ double hi; double lo; } DoubleLength; typedef struct{ double hi; double lo; } DoubleLength;
static const DoubleLength dl_zero = {0.0, 0.0};
static inline DoubleLength static inline DoubleLength
dl_zero() twosum(double a, double b)
{ {
return (DoubleLength) {0.0, 0.0}; double s = a + b;
double ap = s - b;
double bp = s - a;
double da = a - ap;
double db = b - bp;
double t = da + db;
return (DoubleLength) {s, t};
} }
static inline DoubleLength static inline DoubleLength
dl_add(DoubleLength total, double x) dl_add(DoubleLength total, double x)
{ {
double s = total.hi + x; DoubleLength s = twosum(total.hi, x);
double c = total.lo; return (DoubleLength) {s.hi, total.lo + s.lo};
if (fabs(total.hi) >= fabs(x)) {
c += (total.hi - s) + x;
} else {
c += (x - s) + total.hi;
}
return (DoubleLength) {s, c};
} }
static inline DoubleLength static inline DoubleLength
@ -2941,7 +2944,7 @@ math_sumprod_impl(PyObject *module, PyObject *p, PyObject *q)
bool int_path_enabled = true, int_total_in_use = false; bool int_path_enabled = true, int_total_in_use = false;
bool flt_path_enabled = true, flt_total_in_use = false; bool flt_path_enabled = true, flt_total_in_use = false;
long int_total = 0; long int_total = 0;
DoubleLength flt_total = dl_zero(); DoubleLength flt_total = dl_zero;
p_it = PyObject_GetIter(p); p_it = PyObject_GetIter(p);
if (p_it == NULL) { if (p_it == NULL) {
@ -3101,7 +3104,7 @@ math_sumprod_impl(PyObject *module, PyObject *p, PyObject *q)
Py_SETREF(total, new_total); Py_SETREF(total, new_total);
new_total = NULL; new_total = NULL;
Py_CLEAR(term_i); Py_CLEAR(term_i);
flt_total = dl_zero(); flt_total = dl_zero;
flt_total_in_use = false; flt_total_in_use = false;
} }
} }