On Mon, Apr 1, 2013 at 4:02 PM, Sam Lin <[email protected]> wrote:
> Hi Jakob, > > 1. > I still not figure out what does ""Set" in the mathematical sense: the set > of all keys." this mean. > http://en.wikipedia.org/wiki/Set_(mathematics) > > Would you mind to provide a link or some other websites which might to > explain in more detail? > > Thank you. > > Jakob Kummerow於 2013年4月1日星期一UTC+8上午3時59分10秒寫道： >> >> On Sun, Mar 31, 2013 at 4:16 PM, Sam Lin <[email protected]> wrote: >> >>> Hi, >>> >>> 1. Numbers: >>> About the tagging technique, Objects and small integer are both to be >>> set as 32 bits. >>> Further, they use the bottom bit as the tagged value. if the bit is >>> set, then this means that 31 bits are object pointers >>> (Does this mean each bit points to the object accordingly?). >>> Otherwise, then that 31 bits represent integer values. >>> I think my understanding so far is correct. Let me know if I am wrong >>> here. >>> However, I dont really understand why v8 does this and how this >>> tagging technique can improve the performance. >>> >> >> Not having to box numbers is a performance advantage. If you don't box >> them, you need to recognize them somehow, hence the tagging. >> >> >>> >>> 2. Arrays: >>> I went through the slides, there are two types of ways that how v8 >>> handles elements: >>> 1. Fast elements: Linear storage for compact key sets. >>> This is understandable that this one should be very fast. But I >>> dont know what does "key sets" mean here? >>> >> >> "Set" in the mathematical sense: the set of all keys. >> >> >>> 2. Dictionary elements: Hash table storage. >>> The speaker(Google i/o 2012) mentions this one is much more >>> compact than the first one. >>> I thought this one is slower because the v8 switches to this >>> mode because the array is sparse. >>> Why the speaker says this one is more compact? >>> >> >> Dictionary mode allows a compact representation of arrays with sparse key >> sets. >> >> >>> 3. As the speaker gave an example, >>> var A = new Array(); >>> A[0] = 77; >>> A[1] = 88; >>> A[2] = 0.5; >>> A[3] = true; >>> This will cause the hidden class changes a couple of times which >>> cost resources. >>> >>> The better way suggested by v8 is: >>> var A= [77,88,0.5,true]; >>> He said this is a hint to v8. But could any one explain this >>> more specifically on how v8 take this single allocation? >>> >> >> When various object types are listed in the array literal, V8 can see >> right away what kind of stuff will be stored in the array. >> >> Also, for the record, it is generally advisable not to mix types of >> objects stored in an array, especially if some of them are numbers. Arrays >> containing only numbers enable some optimizations that make working with >> them faster. >> >> >>> >>> Some questions here. Thanks for your reply in advance. >>> >>> >>> >>> Regards- >>> >>> >>> >>> -- >>> -- >>> v8-users mailing list >>> [email protected] >>> >>> http://groups.google.com/**group/v8-users<http://groups.google.com/group/v8-users> >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "v8-users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to v8-users+u...@**googlegroups.com. >>> >>> For more options, visit >>> https://groups.google.com/**groups/opt_out<https://groups.google.com/groups/opt_out> >>> . >>> >>> >>> >> >> -- > -- > v8-users mailing list > [email protected] > http://groups.google.com/group/v8-users > --- > You received this message because you are subscribed to the Google Groups > "v8-users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- v8-users mailing list [email protected] http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
