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31 lines
1.2 KiB
Ruby
31 lines
1.2 KiB
Ruby
# frozen_string_literal: true
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module Roundable
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# To paraphrase Wikipedia, most currency pairs are quoted to four decimal
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# places. An exception to this is exchange rates with a value of less than
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# 1.000, which are quoted to five or six decimal places. Exchange rates
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# greater than around 20 are usually quoted to three decimal places and
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# exchange rates greater than 80 are quoted to two decimal places.
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# Currencies over 5000 are usually quoted with no decimal places.
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#
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# https://en.wikipedia.org/wiki/Exchange_rate#Quotations
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def round(value)
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if value > 5000
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value.round
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elsif value > 80
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Float(format('%<value>.2f', value: value))
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elsif value > 20
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Float(format('%<value>.3f', value: value))
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elsif value > 1
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Float(format('%<value>.4f', value: value))
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# I had originally opted to round smaller numbers simply to five decimal
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# places but introduced this refinement to handle an edge case where a
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# lower-rate base currency like IDR produces less precise quotes.
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elsif value > 0.0001
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Float(format('%<value>.5f', value: value))
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else
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Float(format('%<value>.6f', value: value))
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end
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end
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end
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