On Feb 20, 2008, at 1:25 PM, Mark S. Miller wrote: > What numbers are representable as double but not decimal?
Mike Cowlishaw's page at http://www2.hursley.ibm.com/decimal/ is extremely informative, especially http://www2.hursley.ibm.com/decimal/ decifaq.html; see also the link to http://grouper.ieee.org/groups/754/. See http://www2.hursley.ibm.com/decimal/decifaq6.html#bindigits and http://www2.hursley.ibm.com/decimal/decifaq6.html#binapprox for double to decimal conversion answers. As http://wiki.ecmascript.org/ doku.php?id=proposals:decimal summarizes: * A very small amount of precision which may be present in a double- precision binary fp number is lost during a double → decimal promotion, but that: o No precision is lost in an integral → decimal promotion. o Reading a numeric lexeme as a decimal preserves more precision than reading it as a double. > Does decimal have NaN, Infinity, -Infinity, Yes -- from the ES4 RI: >> -1.0m/0.0m -Infinity >> 1.0m/0.0m Infinity >> 0.0m/0.0m NaN > and -0.0? Yes: >> 1.0m/-0.0m -Infinity > (Btw, I never liked -0.0. And I especially dislike ES3's > behavior that 0.0 === -0.0. However, I would argue against making > incompatible changes to this.) Guy Steele edited Edition 1 of ECMA-262 and argued for both of these parts of the standard, based on precedent in related programming languages, as well as advice in IEEE-754 itself. He pointed out something important to numerical programmers: you can walk around the four quadrants using signed zeros with atan2: js> Math.atan2(0,0) 0 js> Math.atan2(-0,0) 0 js> Math.atan2(-0,-0) -3.141592653589793 js> Math.atan2(0,-0) 3.141592653589793 /be _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
