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I was trying to eliminate all the places where we copied a Program
(about 4100 bytes) except for the one final copy into a Box; but that
approach was proving too annoying. Even returning a Program via Result
will cause multiple unnecessary copies that don't optimize out.
This patch switches approaches, and instead allocates a Vec<Instruction>
presized to the correct capacity. This allocation is made as early as
possible and retained for the lifetime of the program if necessary.
This means we'll never avoid a heap allocation, but we can always
avoid extra copies and we don't need a separate Box for interpreted
programs.
Performance effects are subtle. Overall wallclock time doesn't change
much. Cachegrind shows some accesses moving up from RAM to L2 cache.
Using GDB to probe memcpy sizes shows that large (>1024b) memcpy are now
totally gone in the generate-interp test.
Signed-off-by: Micah Elizabeth Scott <[email protected]>
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Making a few comment tweaks suggested in review feedback.
Signed-off-by: Micah Elizabeth Scott <[email protected]>
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In response to review feedback. The byte output is only needed
for unit tests right now, since Equi-X uses u64 output exclusively.
The optimization for shorter output widths can shave tiny amounts of
time off hash benchmarks, but in this case it's more helpful to avoid
introducing APIs that offer parameters with incomplete compile-time
range checking.
Signed-off-by: Micah Elizabeth Scott <[email protected]>
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This refactors the random number generator used within HashX's program
generator so that it uses the rand::RngCore trait. The basic SipHash
powered u64 generator now implements RngCore, while a buffer layer
wraps this and provides u8 and u32 values as needed by the generator.
Some of this new RngCore layer is now exposed to the hashx crate's
public API. The intent is to allow external code to test, benchmark, or
fuzz the program generator by supplying its own random number stream.
Benchmarks show a small but confusing performance improvement
associated with this patch. About a 2% improvement in generation.
This could be due to the Rng changes. No change in compiled hash
execution performance. Even though this patch only touches program
generation, benchmarks show a 4% speedup in interpreted execution.
This seems most likely explained by instruction cache effects,
but I'm not sure.
Signed-off-by: Micah Elizabeth Scott <[email protected]>
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Just running maint/add_warning after the rebase
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This is a new pure Rust implementation of the HashX algorithm
designed by tevador for Tor's onion service proof of work puzzle v1.
HashX is a lightweight family of randomly generated hash functions.
A seed, via blake2 and siphash, drives a program generation model
which randomly selects opcodes and registers while following some
constraints that avoid timing stalls or insufficient hash mixing.
The execution of these hash funcions can be done using a pure Rust
interpreter, or about 20x faster using a very simple just in time
compiler based on the dynasm assembler crate. This has been
implemented for x86_64 and aarch64.
Signed-off-by: Micah Elizabeth Scott <[email protected]>
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