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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/config.h>
#include <vespa/vespalib/stllike/hash_fun.h>
#include <algorithm>
#include <array>
#include <cassert>
#include <ostream>
#include <span>
namespace vespalib::fuzzy {
// Sentinel U32 char for state stepping that cannot match any target string characters
constexpr const uint32_t WILDCARD = UINT32_MAX;
/**
* diag(n) is the width of the diagonal of the cost matrix that can possibly be
* within k edits. This means that for a fixed k, it suffices to maintain state
* for up to and including diag(k) consecutive cells for any given matrix row.
*/
constexpr inline uint8_t diag(uint8_t k) noexcept {
return k*2 + 1;
}
template <uint8_t MaxEdits>
struct FixedSparseState {
private:
static_assert(MaxEdits > 0 && MaxEdits <= UINT8_MAX/2);
std::array<uint32_t, diag(MaxEdits)> indices;
std::array<uint8_t, diag(MaxEdits)> costs; // elems are 1-1 with indices vector
uint8_t sz;
public:
constexpr FixedSparseState() noexcept : indices(), costs(), sz(0) {}
[[nodiscard]] constexpr bool empty() const noexcept {
return (sz == 0);
}
[[nodiscard]] constexpr uint32_t size() const noexcept {
return sz;
}
[[nodiscard]] constexpr uint32_t index(uint32_t entry_idx) const noexcept {
return indices[entry_idx];
}
[[nodiscard]] constexpr uint8_t cost(uint32_t entry_idx) const noexcept {
return costs[entry_idx];
}
// Precondition: !empty()
[[nodiscard]] constexpr uint32_t last_index() const noexcept {
return indices[sz - 1];
}
// Precondition: !empty()
[[nodiscard]] constexpr uint8_t last_cost() const noexcept {
return costs[sz - 1];
}
void append(uint32_t index, uint8_t cost) noexcept {
assert(sz < diag(MaxEdits));
indices[sz] = index;
costs[sz] = cost;
++sz;
}
constexpr bool operator==(const FixedSparseState& rhs) const noexcept {
if (sz != rhs.sz) {
return false;
}
return (std::equal(indices.begin(), indices.begin() + sz, rhs.indices.begin()) &&
std::equal(costs.begin(), costs.begin() + sz, rhs.costs.begin()));
}
struct hash {
size_t operator()(const FixedSparseState& s) const noexcept {
static_assert(std::is_same_v<uint32_t, std::decay_t<decltype(s.indices[0])>>);
static_assert(std::is_same_v<uint8_t, std::decay_t<decltype(s.costs[0])>>);
return (xxhash::xxh3_64(s.indices.data(), s.sz * sizeof(uint32_t)) ^
xxhash::xxh3_64(s.costs.data(), s.sz));
}
};
};
/**
* Prints sparse states as a single matrix row. Columns prior to any state index
* are printed explicitly as '-' characters to make states line up when printed.
*
* Example output for the state (2:1, 3:1):
*
* [-, -, 1, 1]
*
* Only meant as a debugging aid during development, as states with high indices
* will emit very large strings.
*/
template <uint8_t MaxEdits> [[maybe_unused]]
std::ostream& operator<<(std::ostream& os, const FixedSparseState<MaxEdits>& s) {
os << "[";
size_t last_idx = 0;
for (size_t i = 0; i < s.size(); ++i) {
if (i != 0) {
os << ", ";
}
for (size_t j = last_idx; j < s.index(i); ++j) {
os << "-, ";
}
last_idx = s.index(i) + 1;
os << static_cast<uint32_t>(s.cost(i));
}
os << "]";
return os;
}
template <uint8_t MaxEdits>
struct FixedMaxEditsTransitions {
static_assert(MaxEdits > 0 && MaxEdits <= UINT8_MAX/2);
std::array<uint32_t, diag(MaxEdits)> out_u32_chars;
uint8_t size;
constexpr FixedMaxEditsTransitions() noexcept : out_u32_chars(), size(0) {}
[[nodiscard]] constexpr bool has_char(uint32_t u32ch) const noexcept {
for (uint8_t i = 0; i < size; ++i) {
if (out_u32_chars[i] == u32ch) {
return true;
}
}
return false;
}
void add_char(uint32_t u32ch) noexcept {
if (!has_char(u32ch)) {
assert(size < diag(MaxEdits));
out_u32_chars[size] = u32ch;
++size;
}
}
constexpr std::span<const uint32_t> u32_chars() const noexcept {
return {out_u32_chars.begin(), out_u32_chars.begin() + size};
}
constexpr std::span<uint32_t> u32_chars() noexcept {
return {out_u32_chars.begin(), out_u32_chars.begin() + size};
}
void sort() noexcept {
// TODO use custom sorting networks for fixed array sizes <= 5?
// FIXME GCC 12.2 worse-than-useless(tm) warning false positives :I
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Warray-bounds"
std::sort(out_u32_chars.begin(), out_u32_chars.begin() + size);
#pragma GCC diagnostic pop
}
};
template <uint8_t MaxEdits>
struct FixedMaxEditDistanceTraits {
static_assert(MaxEdits > 0 && MaxEdits <= UINT8_MAX/2);
using StateType = FixedSparseState<MaxEdits>;
using TransitionsType = FixedMaxEditsTransitions<MaxEdits>;
constexpr static uint8_t max_edits() noexcept {
return MaxEdits;
}
};
}
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