Mozilla’s new (internal) JavaScript value representation

Re:Mozilla’s new (internal) JavaScript value representation by malkia on Monday August 02, 2010 @10:47PM (#1569920)

The double float tagging using NaN sounds like LuaJIT's approach

quoting http://article.gmane.org/gmane.comp.lang.lua.general/58908

- NaN-tagging: 64 bit tagged values are used for stack slots and table slots. Unboxed floating-point numbers (doubles) are overlayed with tagged object references. The latter can be distinguished from numbers via the use of special NaNs as tags. It's a remote descendant of pointer-tagging.

  [The idea dates back to 2006, but I haven't disclosed it before
  2008. Special NaNs have been used to overlay pointers before.
  Others have used it for tagging later on. The specific layout is
  of my own devising.]

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Re:Mozilla’s new (internal) JavaScript value representation by andhow on Tuesday August 03, 2010 @01:37AM (#1570244)

It is also used in WebKit's JSC. Using the NaN space goes back much further than LuaJIT. E.g., you can see it mention in this 1993 survey paper: http://lambda-the-ultimate.org/node/3912.

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Re:Mozilla’s new (internal) JavaScript value representation by malkia on Tuesday August 03, 2010 @04:45PM (#1572685)

Thanks for the paper! Quite interesting and easy read.

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