POC of accurate_to_s
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require "bigdecimal" | |
class Float | |
HEX_FORMAT = /(-?)0x([01])\.?([0-9a-f]*)p([+-][0-9]*)/ | |
BIG_DECIMAL_2 = BigDecimal(2) | |
def accurate_to_s | |
bin_str = "%a" % [self] | |
mat = HEX_FORMAT.match bin_str | |
sgn, msbit, bits, ex = mat[1, 4] | |
if msbit == "0" then | |
unless bits == "" and ex == "+0" then | |
raise "assertion error" | |
end | |
return "#{sgn}0" | |
end | |
result = BigDecimal((sgn+msbit+bits).to_i 16) | |
ex = ex.to_i - bits.length * 4 | |
case ex <=> 0 | |
when 1 then # ex > 0 | |
result *= 2**ex | |
when -1 then # ex < 0 | |
result *= BIG_DECIMAL_2**ex | |
end | |
return result.to_s | |
end | |
end | |
class Rational | |
BIG_DECIMAL_2 = BigDecimal(2) | |
BIG_DECIMAL_5 = BigDecimal(5) | |
def accurate_to_s | |
deno = self.denominator | |
if deno == 1 then | |
return self.numerator.to_s | |
end | |
tmp = deno | |
t_2 = 0 | |
t_5 = 0 | |
loop { | |
q, r = tmp.divmod 2 | |
break if r != 0 | |
tmp = q | |
t_2 += 1 | |
} | |
loop { | |
q, r = tmp.divmod 5 | |
break if r != 0 | |
tmp = q | |
t_5 += 1 | |
} | |
if tmp != 1 then | |
return nil | |
end | |
result = BigDecimal(self.numerator) | |
result *= BIG_DECIMAL_2**-t_2 | |
result *= BIG_DECIMAL_5**-t_5 | |
return result.to_s | |
end | |
end | |
alias BigDecimal_ORIG BigDecimal | |
def BigDecimal val, *args | |
if args == [nil] then | |
if val.respond_to? :accurate_to_s then | |
result = val.accurate_to_s | |
if result then | |
return BigDecimal_ORIG(result) | |
end | |
end | |
end | |
BigDecimal_ORIG val, *args | |
end | |
if $0 == __FILE__ | |
x = 0.1 | |
puts BigDecimal(x, nil).to_s | |
puts BigDecimal(Rational(x), nil).to_s | |
end |
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http://bugs.ruby-lang.org/issues/8295