Fix frame vector size

[nsavoire]

push_back is replaced by direct indexing since std::vector<uintptr_t> output(n); already creates a a vector with n elements (set to 0).

[github-actions]

Overall package size

Self size: 1.44 MB
Deduped: 8.3 MB
No deduping: 8.31 MB

Dependency sizes

name	version	self size	total size
protobufjs	7.1.2	2.76 MB	6.55 MB
source-map	0.7.4	226 kB	226 kB
split	1.0.1	12.29 kB	24.82 kB
findit2	2.2.3	14.78 kB	14.78 kB
p-limit	3.1.0	7.75 kB	13.78 kB
delay	5.0.0	11.17 kB	11.17 kB
pify	5.0.0	8.87 kB	8.87 kB
node-gyp-build	3.9.0	8.81 kB	8.81 kB

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[r1viollet]

indeed we already resize it here

[Qard]

LGTM. Just curious, is there any perf difference between the two if the size is already set? I pretty much just used push_back out of habit. 😅

[nsavoire]

LGTM. Just curious, is there any perf difference between the two if the size is already set? I pretty much just used push_back out of habit. 😅

The issue here is not performance: std::vector<uintptr_t> output(n); creates a vector with n elements (all set to zero).
Then each push_back will add another element, so in the end output has 2n elements with the first n elements being 0.
To insert n elements in a vector, you can:

• Create an empty vector (std::vector<uintptr_t> output;) and then use push_back. Vector will resize itself by doubling its capacity accordingly.
• You can improve the previous if you know the number of items in advance, by using output.reserve(n); to pre-allocate the vector to its final capacity.
• Construct the vector with n elements (as done in this PR), the elements will be value initialized (ie. set to zero in the case of ints) and then set the value of each elements by indexing the vector. For ints, this approach might be a little bit faster than the previous one, but for elements that are costlier to value initialize, the previous one would be better.

[Qard]

Ah, good to know. For some reason I was thinking it worked like output.reserve(n). Good catch! 😅