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Fixed Integers representing numbers bigger than 20 decimal digits fail double conversion #204

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Ravenwater opened this issue Dec 26, 2020 · 1 comment
Closed

Fixed Integers representing numbers bigger than 20 decimal digits fail double conversion #204

Ravenwater opened this issue Dec 26, 2020 · 1 comment
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bug good first issue numerical investigation Investigation to explain/quantify numerical properties of a calculation
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V3

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@Ravenwater
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In generating the tribonacci constant we encounter this:

oracle : 1.8392867552141611325518525646532866004241787460975922467787586394042032220819
612979045863284352 : double(612979045863284359)
    70 : 1.83928675521416096216853475198
1127444240280152704 : double(1127444240280152749)
    71 : 1.83928675521416118421313967701
2073693258389777152 : double(2073693258389777176)
    72 : 1.83928675521416118421313967701
3814116544533214208 : double(3814116544533214284)
    73 : 1.83928675521416118421313967701
7015254043203144704 : double(7015254043203144209)
    74 : 1.83928675521416140625774460204
-5543680227583416320 : double(12903063846126135669)
    75 : -0.790232284311144894672906957567
5285690360152942592 : double(23732434433862494162)
    76 : -0.953462346881624567274116088811
6757264175772670976 : double(43650752323191774040)
    77 : 1.2784071172071358457600354086
6499274308342197248 : double(80286250603180403871)
    78 : 0.961820366834929441068879896193
95484770558259152 : double(147669437360234672073)
    79 : 0.0146916049436009929496371739788

At T(75) the Tribonacci number is 12903063846126135669 but the double conversion incorrectly generates -5543680227583416320.

Hypothesis: that number is 20 digits, which would require 66 bits to represent. Extended precision only has 64 bits. Need to revisit the conversion algorithm.
@Ravenwater Ravenwater added this to the V3 milestone Dec 26, 2020
@Ravenwater Ravenwater changed the title Integers bigger than 20 decimal digits fail double conversion Fixed Integers representing numbers bigger than 20 decimal digits fail double conversion Jan 1, 2021
@Ravenwater Ravenwater added the numerical investigation Investigation to explain/quantify numerical properties of a calculation label Jan 1, 2021
@Ravenwater
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fixed in V3.40.1

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