What happens if you combine 'new Array(length)' + 'array[length - 1] = <default value>'? That seems like it would produce the optimal behavior in all cases.
On Wed, Jul 16, 2014 at 11:40 PM, Nicholas Nethercote <[email protected]> wrote: > On a related note: ObjectElements::VALUES_PER_HEADER is 2. Is this > because 2 * sizeof(HeapSlot) is 16 bytes, which is equal to > sizeof(ObjectElements)? > > Nick > > On Wed, Jul 16, 2014 at 11:34 PM, Nicholas Nethercote > <[email protected]> wrote: >> On Wed, Jul 16, 2014 at 11:08 PM, Nicholas Nethercote >> <[email protected]> wrote: >>> Hi, >>> >>> Here's some code from pdf.js: >>> >>> function stringToArray(str) { >>> var length = str.length; >>> var array = []; >>> for (var i = 0; i < length; ++i) { >>> array[i] = str.charCodeAt(i); >>> } >>> return array; >>> } >>> >>> This kind of code shows up in a number of places in pdf.js. Pretty >>> simple -- filling in an array one element at a time. >>> >>> Underneath the covers, this causes the array to repeatedly double in >>> size, which is annoying. And I thought I could avoid it because we >>> know how big the array will be in advance. So I changed the 3rd line >>> to this: >>> >>> var array = new Array(length); >>> >>> but I still get the same sort of doubling behaviour under the covers. >> >> Oh wait. It depends on the value of |length|. If it's 2050 or less, >> then the right-sized array is allocated immediately. Otherwise, it >> allocates 10 elements and then does the doubling thing. I guess >> there's a limit to how much we'll pre-allocate. >> >> So using |new Array(length)| seems like the best thing, then. >> >> Nick > _______________________________________________ > dev-tech-js-engine-internals mailing list > [email protected] > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals _______________________________________________ dev-tech-js-engine-internals mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
