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bpo-41513: Improve speed and accuracy of math.hypot() #21803

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Merged
rhettinger merged 10 commits into from
Aug 16, 2020
+44 −6
Merged

bpo-41513: Improve speed and accuracy of math.hypot() #21803

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e2b1b38
frexp/ldexp variant
rhettinger Aug 8, 2020
7cb895d
Multiply by power of two variant
rhettinger Aug 8, 2020
2d586b1
Strengthen assertions
rhettinger Aug 9, 2020
c15ce79
Added notes and commented out assertions to reach a stable resting point
rhettinger Aug 9, 2020
c853597
Two code paths. All tests pass.
rhettinger Aug 9, 2020
03ec58b
Clean-up comments and ranges
rhettinger Aug 10, 2020
ebf6a31
Remove debugging code
rhettinger Aug 10, 2020
4742ef8
Clean-up comments and over-specified tests
rhettinger Aug 10, 2020
5e9f1a9
Add blurb
rhettinger Aug 10, 2020
5c6478f
Improve the comments.
rhettinger Aug 15, 2020
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frexp/ldexp variant
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@rhettinger
rhettinger committed Aug 8, 2020
commit e2b1b385c9bc3d2b081d1e1895849bf48f5e843c
9 changes: 7 additions & 2 deletions Modules/mathmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2438,6 +2438,7 @@ static inline double
vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
{
double x, csum = 1.0, oldcsum, frac = 0.0;
int max_e;
Py_ssize_t i;

if (Py_IS_INFINITY(max)) {
Expand All @@ -2449,17 +2450,21 @@ vector_norm(Py_ssize_t n, double *vec, double max, int found_nan)
if (max == 0.0 || n <= 1) {
return max;
}
frexp(max, &max_e);
for (i=0 ; i < n ; i++) {
int e;

x = vec[i];
assert(Py_IS_FINITE(x) && fabs(x) <= max);
x /= max;
x = frexp(x, &e);
x = ldexp(x, e - max_e);
x = x*x;
oldcsum = csum;
csum += x;
assert(csum >= x);
frac += (oldcsum - csum) + x;
}
return max * sqrt(csum - 1.0 + frac);
return ldexp(sqrt(csum - 1.0 + frac), max_e);
}

#define NUM_STACK_ELEMS 16
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