27 lines
1.1 KiB
Markdown
27 lines
1.1 KiB
Markdown
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# Comparisons & ranges {#comparisons}
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A distributed comparison function returns a payload when a predicate holds
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on the secret point. Shares are additive: `reconstruct` adds them.
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| Call | When it is hot |
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| --- | --- |
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| `dpf::lt` / `leq` / `gt` / `geq` | The public query is on that side of the secret point |
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| `dpf::eq` | The public query equals the secret point |
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| `dpf::ic` | The secret point lies in a public interval |
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| `dpf::idcf` / `cmp_prefix<L>` | A correction at every depth, or only the first `L` bits |
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| `dpf::block_width<B>` | Ring words only at checkpoints `B` levels apart |
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```cpp
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auto [k0, k1] = dpf::make_dpf(std::uint8_t{40}, dpf::gt(std::uint64_t{1}));
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auto opened = dpf::reconstruct(
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dpf::eval_point(dpf::cmp, k0, std::uint8_t{50}),
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dpf::eval_point(dpf::cmp, k1, std::uint8_t{50}));
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// opened == 1
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```
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A wildcard comparison payload is filled later with `assign_cmp`.
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Eval before that throws.
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**Go deeper:** [dcf.hpp](@ref dpf/dcf.hpp), [interval.hpp](@ref dpf/interval.hpp),
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[blocked_dcf.hpp](@ref dpf/blocked_dcf.hpp), [F_DCF](@ref dcf.hpp).
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