Make sorting stable #5236
Make sorting stable #5236
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| i = ht->nNumUsed; | ||
| /* Store original order of elements in extra space to allow stable sorting. */ | ||
| for (i = 0; i < ht->nNumUsed; i++) { | ||
| Z_EXTRA(ht->arData[i].val) = i; |
nikic
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But call with reversed operands to make sure it continues working.
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@nikic Huge thumb up for addressing this! Did you also considered using more and more popular Timsort algorithm? It is stable by default with the same complexity. Now also used by Java and C#. |
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@mvorisek Switching to Timsort is a more intrusive change. It's a different algorithm (hybrid merge rather than hybrid quick) with different performance characteristics (and more importantly, memory usage characteristics). If you want to evaluate Timsort usage in PHP, I'm definitely interested in results. |
I would love to help, but my C skills are limited. I have done now more reseach on this: Usage: default also in JS/V8, Python Benchmarks:
Memory complexity is |
| if (!ARRAYG(compare_deprecation_thrown)) { | ||
| php_error_docref(NULL, E_DEPRECATED, | ||
| "Returning bool from comparison function is deprecated, " | ||
| "return an integer less than, equal to, or greater than zero"); |
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an integer less than, equal to, or greater than zero
Isn't that a little redundant? (as it basically includes all integers). Alternatively we could say "-1, 0 or 1".
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Yes, this is intentionally redundant to clarify meaning of the value. I used "-1, 0 or 1" here initially, but as @hikari-no-yume pointed out on the mailing list, there is no actual requirement to return one of those here, and some functions like strcmp() which are reasonable to use in this context don't return -1, 0, 1 specifically.
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There could be a better way to word it, but there is a risk of the message being too long…
RFC: https://wiki.php.net/rfc/stable_sorting
This makes the array sorting functions stable (mostly relevant for usort). This does not actually change the core sorting algorithm to be stable (it is still a quick sort). Instead, we store the position of the original elements and use that as a fallback comparison criterion. Due to the way hashtable sorting works, we can do this very cheaply, and without additional memory overhead.