[issue41513] Scale by power of two in math.hypot()
Tim Peters
report at bugs.python.org
Tue Aug 18 23:46:08 EDT 2020
Tim Peters <tim at python.org> added the comment:
Here's a "correct rounding" fail for the add_on approach:
xs = [16.000000000000004] * 9
decimal result = 48.00000000000001065814103642
which rounds to float 48.000000000000014
add_on result: 48.00000000000001
That's about 0.5000000000026 ulp too small - shocking ;-)
The fsum approach got this one right, but has similar failures on other inputs of the same form; i.e.,
[i + ulp(i)] * 9
for various integers `i`.
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