On Thu, 4 Jul 2024 13:35:36 GMT, Johan Sjölen <jsjo...@openjdk.org> wrote:
>> Hi, >> >> Today the GrowableArray has a set index type of `int`, this PR makes it so >> that you can set your own index type through a template parameter. >> >> This opens up for a few new design choices: >> >> - Do you know that you have a very small array? Use an `uint8_t` for len and >> cap, each. >> - Do you have a very large one? Use an `uint64_t`. >> >> The code has opted for `int` being default, as to keep identical semantics >> for all existing code and to let users not have to worry about the index if >> they don't care. >> >> One "major" change that I don't want to get lost in the review: I've changed >> the mid-point calculation to be overflow insensitive without casting. >> >> >> >> // Old >> mid = ((max + min) / 2); >> // New >> mid = min + ((max - min) / 2); >> >> Some semi-rigorous thinking: >> min \in [0, len) >> max \in [0, len) >> min <= max >> max - min / 2 \in [0, len/2) >> Maximizing min and max => len + 0 >> Maximizing max, minimizing min => len/2 >> Minimizing max, maximizing min => max = min => min >> >> >> // Proof that they're identical when m, h, l \in N >> (1) m = l + (h - l) / 2 <=> >> 2m = 2l + h - l = h + l >> >> (2) m = (h + l) / 2 <=> >> 2m = h + l >> (1) = (2) >> QED > > Johan Sjölen has updated the pull request incrementally with one additional > commit since the last revision: > > Attempt at fixing GA VMStruct Always fun to grapple with vmStructs, moving this back to draft. ------------- PR Comment: https://git.openjdk.org/jdk/pull/20031#issuecomment-2209022728
