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SijaRX14
Sija
authored and
RX14
committedJan 20, 2018
BigDecimal.new(str : String) handles scientific notation (#5582)
* BigDecimal.new(str : String) handles scientific notation * fixup! by @RX14 * Spec with cases suggested by @RX14 * Fix failing spec * Fixed another failing case
·
1.16.00.25.0
1 parent 3515968 commit ddbcf6c

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+66
-8
lines changed

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+66
-8
lines changed
 

‎spec/std/big/big_decimal_spec.cr

+19
Original file line numberDiff line numberDiff line change
@@ -183,6 +183,25 @@ describe BigDecimal do
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1.5.to_big_f.to_big_d.should eq (BigDecimal.new(15, 1))
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end
185185

186+
it "can be converted from scientific notation" do
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"10.01e1".to_big_d.should eq (BigDecimal.new("100.1"))
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"10.01e-1".to_big_d.should eq (BigDecimal.new("1.001"))
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"6.033e2".to_big_d.should eq (BigDecimal.new("603.3"))
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"603.3e-2".to_big_d.should eq (BigDecimal.new("6.033"))
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"-0.123e12".to_big_d.should eq (BigDecimal.new("-123000000000"))
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"0.123e12".to_big_d.should eq (BigDecimal.new("123000000000"))
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"0.123e+12".to_big_d.should eq (BigDecimal.new("123000000000"))
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"-0.123e-7".to_big_d.should eq (BigDecimal.new("-0.0000000123"))
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"-0.1e-7".to_big_d.should eq (BigDecimal.new("-0.00000001"))
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"0.1e-7".to_big_d.should eq (BigDecimal.new("0.00000001"))
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"1.0e-8".to_big_d.should eq (BigDecimal.new("0.00000001"))
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"10e-8".to_big_d.should eq (BigDecimal.new("0.0000001"))
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"1.0e+8".to_big_d.should eq (BigDecimal.new("100000000"))
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"10e+8".to_big_d.should eq (BigDecimal.new("1000000000"))
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"10E+8".to_big_d.should eq (BigDecimal.new("1000000000"))
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"10E8".to_big_d.should eq (BigDecimal.new("1000000000"))
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end
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it "is comparable with other types" do
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BigDecimal.new("1.0").should eq BigDecimal.new("1")
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BigDecimal.new("1").should eq BigDecimal.new("1.0")

‎src/big/big_decimal.cr

+47-8
Original file line numberDiff line numberDiff line change
@@ -50,39 +50,78 @@ struct BigDecimal < Number
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raise InvalidBigDecimalException.new(str, "Zero size") if str.bytesize == 0
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53-
# Check str's validity and find index of .
53+
# Check str's validity and find index of '.'
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decimal_index = nil
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# Check str's validity and find index of 'e'
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exponent_index = nil
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str.each_char_with_index do |char, index|
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case char
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when '-'
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if index != 0
61+
unless index == 0 || exponent_index == index - 1
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raise InvalidBigDecimalException.new(str, "Unexpected '-' character")
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end
64+
when '+'
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unless exponent_index == index - 1
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raise InvalidBigDecimalException.new(str, "Unexpected '+' character")
67+
end
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when '.'
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if decimal_index
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raise InvalidBigDecimalException.new(str, "Unexpected '.' character")
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end
65-
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decimal_index = index
73+
when 'e', 'E'
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if exponent_index
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raise InvalidBigDecimalException.new(str, "Unexpected #{char.inspect} character")
76+
end
77+
exponent_index = index
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when '0'..'9'
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# Pass
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else
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raise InvalidBigDecimalException.new(str, "Unexpected #{char.inspect} character")
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end
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end
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85+
decimal_end_index = (exponent_index || str.bytesize) - 1
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if decimal_index
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decimal_count = (decimal_end_index - decimal_index).to_u64
88+
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value_str = String.build do |builder|
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# We know this is ASCII, so we can slice by index
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builder.write(str.to_slice[0, decimal_index])
78-
builder.write(str.to_slice[decimal_index + 1, str.bytesize - decimal_index - 1])
92+
builder.write(str.to_slice[decimal_index + 1, decimal_count])
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end
80-
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@value = value_str.to_big_i
82-
@scale = (str.bytesize - decimal_index - 1).to_u64
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else
84-
@value = str.to_big_i
85-
@scale = 0_u64
96+
decimal_count = 0_u64
97+
@value = str[0..decimal_end_index].to_big_i
98+
end
99+
100+
if exponent_index
101+
exponent_postfix = str[exponent_index + 1]
102+
case exponent_postfix
103+
when '+', '-'
104+
exponent_positive = exponent_postfix == '+'
105+
exponent = str[(exponent_index + 2)..-1].to_u64
106+
else
107+
exponent_positive = true
108+
exponent = str[(exponent_index + 1)..-1].to_u64
109+
end
110+
111+
@scale = exponent
112+
if exponent_positive
113+
if @scale < decimal_count
114+
@scale = decimal_count - @scale
115+
else
116+
@scale -= decimal_count
117+
@value *= 10.to_big_i ** @scale
118+
@scale = 0_u64
119+
end
120+
else
121+
@scale += decimal_count
122+
end
123+
else
124+
@scale = decimal_count
86125
end
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end
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