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sqrt hangs on some inputs #32

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devast8a opened this issue Oct 28, 2023 · 3 comments
Closed

sqrt hangs on some inputs #32

devast8a opened this issue Oct 28, 2023 · 3 comments

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@devast8a
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For some inputs dec64_sqrt can enter an infinite loop where it will not converge on a result and will instead oscillate between two values forever. It seems to be related to rounding behavior within dec64_divide. Printing both the coefficient and the exponent of progress, we get the following log from dec64_sqrt(dec64_make(36040, 0))

9011000000000000 -12
4507499778049051 -12
22577476706966965 -13
11368552409916279 -13
5842783632731283 -13
3229806454536597 -13
2172831395833602 -13
19157483389377885 -14
18984987616317365 -14
1898420397630861 -13
18984203960134855 -14
1898420396013486 -13
18984203960134855 -14
1898420396013486 -13
18984203960134855 -14
1898420396013486 -13
18984203960134855 -14
1898420396013486 -13
18984203960134855 -14
1898420396013486 -13
...
@douglascrockford
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So what is your fix?

@devast8a devast8a mentioned this issue Oct 28, 2023
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@devast8a
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Not sure, bounding the loop might be acceptable in the short term. In the long term, probably adopting another algorithm.

@douglascrockford
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Please submit a fix.

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@douglascrockford @devast8a