The document discusses the difficulties of using floating point numbers (Floats) in Ruby and proposes using Rational numbers instead. Some key issues mentioned are that Floats are represented internally as binary which can lead to representation errors, they describe a range rather than a specific number, and calculations with Floats may not be equal due to rounding errors. As an alternative, Rational numbers represented using a decimal notation could solve these problems, though they may be slower. Overall the document argues that Rational is a better fit than Float for many use cases in Ruby.

1. The world without the
literal notation for
floating-point numbers
, Kenta Murata
GeneticLab Co., Ltd.
Tuesday, July 19, 2011 1

2. CRuby Committer
(BigDecimal)
Ruby Sapporo
Kosen Conf
http://www.flickr.com/photos/koichiroo/5244581973/
Tuesday, July 19, 2011 2

3. Tuesday, 1
2010 3 July 19, 2011 3

4. RubyKaigi
n !!
Tuesday, 1
2010 3 July 19, 2011 4

5. Ruby 04
Sapporo RubyKaigi 04
Summer 2012
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6. I have some question.
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7. Do you use Float
values?
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8. Do you understand
Float well?
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9. Float is too difficult.
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10. Reading difficulty
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11. ruby-1.9.2-p290 :001 > 76287755398823936.0
=> 76287755398823940.0
ruby-1.9.2-p290 :002 >
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12. Comparing difficulty
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13. ruby-1.9.2-p290 :001 > 12.4 * 1.05 == 13.02
=> false
ruby-1.9.2-p290 :002 > 12.4 * 1.05
=> 13.020000000000001
ruby-1.9.2-p290 :003 >
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14. Representation
difference
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15. Human:
Decimal
Internal:
Binary
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16. Concept
difference
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17. We think
Float is a number.
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18. It is real that
Float is a range.
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19. They’re troublesome
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20. There is a solution
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21. Why not use Rational.
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22. It is difficult, too.
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23. Ruby doesn’t have
any literal notations
for Rational
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24. Does a fractional
notation solve the
problems?
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25. No!
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26. We naturally use
decimal point notation.
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27. We need a decimal-
point notation for
representing a Rational.
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28. ruby--p290 :001 > 13.02.class
=> Rational
ruby--p290 :001 > 12.4 * 1.05 == 13.02
=> true
ruby-1.9.2-p290 :002 > 12.4 * 1.05
=> 13.02
ruby-1.9.2-p290 :003 > 13.02 / 3
=> (217/50)
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29. Do you worry about
Rational is slow?
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30. We can optimize for
denominators of 10n
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31. Float isn’t as so fast as
you think
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32. If you need fast Float
calculation
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33. Write it in C as
extension library
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34. If you need to calculate
with arrays of Float
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35. Use NArray
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36. Rational may be
what you want
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37. This talk’s background,
demonstrations, and
more detail descriptions
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38. Tuesday, July 19, 2011 38