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require File.expand_path('../../../spec_helper', __FILE__)
require 'bigdecimal'
describe "BigDecimal#sub" do
before(:each) do
@one = BigDecimal("1")
@zero = BigDecimal("0")
@two = BigDecimal("2")
@nan = BigDecimal("NaN")
@infinity = BigDecimal("Infinity")
@infinity_minus = BigDecimal("-Infinity")
@one_minus = BigDecimal("-1")
@frac_1 = BigDecimal("1E-99999")
@frac_2 = BigDecimal("0.9E-99999")
end
it "returns a - b with given precision" do
# documentation states, that precision is optional
# but implementation raises ArgumentError if not given.
@two.sub(@one, 1).should == @one
@one.sub(@two, 1).should == @one_minus
@one.sub(@one_minus, 1).should == @two
@frac_2.sub(@frac_1, 1000000).should == BigDecimal("-0.1E-99999")
@frac_2.sub(@frac_1, 1).should == BigDecimal("-0.1E-99999")
# the above two examples puzzle me.
in_arow_one = BigDecimal("1.23456789")
in_arow_two = BigDecimal("1.2345678")
in_arow_one.sub(in_arow_two, 10).should == BigDecimal("0.9E-7")
@two.sub(@two,1).should == @zero
@frac_1.sub(@frac_1, 1000000).should == @zero
end
it "returns NaN if NaN is involved" do
@one.sub(@nan, 1).nan?.should == true
@nan.sub(@one, 1).nan?.should == true
end
it "returns NaN if both values are infinite with the same signs" do
@infinity.sub(@infinity, 1).nan?.should == true
@infinity_minus.sub(@infinity_minus, 1).nan?.should == true
end
it "returns Infinity or -Infinity if these are involved" do
@infinity.sub(@infinity_minus, 1).should == @infinity
@infinity_minus.sub(@infinity, 1).should == @infinity_minus
@zero.sub(@infinity, 1).should == @infinity_minus
@frac_2.sub( @infinity, 1).should == @infinity_minus
@two.sub(@infinity, 1).should == @infinity_minus
end
end
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