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Joe Tsai 539c5e44c5 util/deephash: always keep values addressable (#5328) ... The logic of deephash is both simpler and easier to reason about if values are always addressable. In Go, the composite kinds are slices, arrays, maps, structs, interfaces, pointers, channels, and functions, where we define "composite" as a Go value that encapsulates some other Go value (e.g., a map is a collection of key-value entries). In the cases of pointers and slices, the sub-values are always addressable. In the cases of arrays and structs, the sub-values are always addressable if and only if the parent value is addressable. In the case of maps and interfaces, the sub-values are never addressable. To make them addressable, we need to copy them onto the heap. For the purposes of deephash, we do not care about channels and functions. For all non-composite kinds (e.g., strings and ints), they are only addressable if obtained from one of the composite kinds that produce addressable values (i.e., pointers, slices, addressable arrays, and addressable structs). A non-addressible, non-composite kind can be made addressable by allocating it on the heap, obtaining a pointer to it, and dereferencing it. Thus, if we can ensure that values are addressable at the entry points, and shallow copy sub-values whenever we encounter an interface or map, then we can ensure that all values are always addressable and assume such property throughout all the logic. Performance: name old time/op new time/op delta Hash-24 21.5µs ± 1% 19.7µs ± 1% -8.29% (p=0.000 n=9+9) HashPacketFilter-24 2.61µs ± 1% 2.62µs ± 0% +0.29% (p=0.037 n=10+9) HashMapAcyclic-24 30.8µs ± 1% 30.9µs ± 1% ~ (p=0.400 n=9+10) TailcfgNode-24 1.84µs ± 1% 1.84µs ± 2% ~ (p=0.928 n=10+10) HashArray-24 324ns ± 2% 332ns ± 2% +2.45% (p=0.000 n=10+10) Signed-off-by: Joe Tsai <joetsai@digital-static.net>		2 years ago
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testtype	util/deephash: fix unexported time.Time hashing	2 years ago
deephash.go	util/deephash: always keep values addressable (#5328)	2 years ago
deephash_test.go	util/deephash: always keep values addressable (#5328)	2 years ago