Safe addition: Difference between revisions
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(→{{header|C}}: Add solution with Microsoft _controlfp().) |
(→{{header|REXX}}: Add Ruby using bigdecimal.) |
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numeric digits digits()+digits()%10 /*increase digits by 10%.*/ |
numeric digits digits()+digits()%10 /*increase digits by 10%.*/ |
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</lang> |
</lang> |
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=={{header|Ruby}}== |
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The <tt>Float</tt> class provides no way to change the rounding mode. We instead use the <tt>BigDecimal</tt> class from the standard library. <tt>BigDecimal</tt> is a floating-point number of radix 10 with arbitrary precision. |
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When adding <tt>BigDecimal</tt> values, <tt>a + b</tt> is always safe. This example uses <tt>a.add(b, prec)</tt>, which is not safe because it rounds to <tt>prec</tt> digits. This example computes a safe interval by rounding to both floor and ceiling. |
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{{libheader|bigdecimal}} |
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<lang ruby>require 'bigdecimal' |
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require 'bigdecimal/util' # String#to_d |
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def safe_add(a, b, prec) |
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a, b = a.to_d, b.to_d |
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rm = BigDecimal::ROUND_MODE |
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orig = BigDecimal.mode(rm) |
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BigDecimal.mode(rm, BigDecimal::ROUND_FLOOR) |
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low = a.add(b, prec) |
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BigDecimal.mode(rm, BigDecimal::ROUND_CEILING) |
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high = a.add(b, prec) |
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BigDecimal.mode(rm, orig) |
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low..high |
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end |
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[["1", "2"], |
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["0.1", "0.2"], |
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["0.1", "0.00002"], |
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["0.1", "-0.00002"], |
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].each { |a, b| puts "#{a} + #{b} = #{safe_add(a, b, 3)}" }</lang> |
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Output: <pre>1 + 2 = 0.3E1..0.3E1 |
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0.1 + 0.2 = 0.3E0..0.3E0 |
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0.1 + 0.00002 = 0.1E0..0.101E0 |
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0.1 + -0.00002 = 0.999E-1..0.1E0</pre> |
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=={{header|Tcl}}== |
=={{header|Tcl}}== |
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