The document discusses the difficulties of using floating point numbers (Floats) in Ruby and proposes using Rational numbers instead. Some key points made include: - Floats are stored internally as binary which can lead to representation errors, while we think of them as decimal numbers - Floats actually represent a range of values rather than a single number - Using Rational would allow keeping numbers as exact fractions, avoiding errors from Float representations - While Rational may seem slower, optimizations are possible for common denominators and FastMath libraries could be used for Floats if needed

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