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Justin wrote: > Craig Ringer wrote: >> `double' in C++ refers to double precision floating point. `double' is >> subject to all the usual fun with rational decimals being irrational >> binary floats (and vice versa). > Not according to MS specific if i'm reading it correctly > > *Microsoft Specific >* > > The double type contains 64 bits: 1 for sign, 11 for the exponent, and > 52 for the mantissa. Its range is +/--1.7E308 with at least 15 digits of > precision I take it you're referring to: http://msdn.microsoft.com/en-us/library/e02ya398(VS.80).aspx ? See how it says "The format is similar to the float format...." ? As you can see from: http://msdn.microsoft.com/en-us/library/hd7199ke(VS.80).aspx the `double' type is a binary floating point representation, just like float. It just has a bigger exponent and a bigger mantissa, so it can represent more extreme values and do so with more precision. Being a binary floating point representation it's subject to all the usual problems with comparison for equality, rounding oddities, etc. Here's one of the many explanations out there on the 'net. I haven't read this particular one, it's just a viable looking Google hit: http://www.cprogramming.com/tutorial/floating_point/understanding_floating_point.html By the way, there was at least a proposal for a numeric/decimal type for C++0x . It doesn't seem to have made the cut. http://209.85.173.104/search?q=cache:D0Iqhgz7X1QJ:www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2041.pdf+%22c%2B%2B0x%22+decimal+OR+numeric&hl=en&ct=clnk&cd=1&gl=au&client=firefox-a http://en.wikipedia.org/wiki/C%2B%2B0x http://www.open-std.org/jtc1/sc22/wg21/docs/papers/ It looks like ISO C might adopt a decimal type or library though: http://www2.hursley.ibm.com/decimal/ Note in particular the support in gcc 4.2 or newer. There's also a library: http://www2.hursley.ibm.com/decimal/dfpal/ that might be useful. -- Craig Ringe
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