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- Date: Sun, 25 Oct 2009 10:10:15 +0000
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http://www.w3.org/Bugs/Public/show_bug.cgi?id=8047 Philip Taylor <excors@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |excors@gmail.com Status|RESOLVED |REOPENED Keywords| |NE Resolution|FIXED | --- Comment #3 from Philip Taylor <excors@gmail.com> 2009-10-25 10:10:14 --- It seems clearer now, but weird, because it doesn't match how floats are parsed in ECMAScript (or any other environments I'm aware of, though that's not many). E.g. the string "1.00000000000000012" in common ECMAScript implementations gets converted to the number 1.0000000000000002 (and if you subtract 1 then you get 2.220446049250313e-16) whereas HTML5 now just talks about "truncating", so it would end up with the number 1.0 (being the next lowest representable number). I don't see any reason to differ from ES, and doing so seems like it could make implementations more complex (since they couldn't be based on existing float-parsing code). ES defines ToNumber as truncating after the 20th significant digit and then (optionally) incrementing the 20th significant digit, and then doing round-to-nearest with ties-to-even. But these are (32-bit) floats, not Numbers, so HTML5 can't do exactly the same. It might be better to copy the definition from http://dev.w3.org/2006/webapi/WebIDL/#es-float , saying something like: "A number n is <dfn>converted to an IDL float value</dfn> by running the following algorithm: 1. Let S be the set of finite IEEE 754 single-precision floating point values except −0, but with two special values added: 2^128 and −2^128. 2. Let V be the number in S that is closest to n, selecting the number with an even significand if there are two equally close values. (The two special values 2^128 and −2^128 are considered to have even significands for this purpose.) 3. If V is 2^128, return +∞. 4. If V is −2^128, return −∞. 5. Return V. ... If a reflecting IDL attribute is a floating point number type (float), then, on getting, the content attribute must be parsed according to the rules for parsing floating point number values, and if that is successful, the number must be <a href>converted to an IDL float value</a>; and if the resulting value is finite, then that value must be returned. If, on the other hand, the parsing fails or the conversion returns an infinite value, ..." (n can't be NaN or −0, so those cases aren't handled here.) I doubt that is perfectly correct (perhaps n needs to be truncated before rounding?), and it would be good if someone who understands floating point parsing properly could suggest something better, but I think this is better than what the spec says now. -- Configure bugmail: http://www.w3.org/Bugs/Public/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.

Received on Sunday, 25 October 2009 10:10:19 UTC