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175 lines
5.3 KiB
C++
175 lines
5.3 KiB
C++
//
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// Dispatcher.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 17/03/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#ifndef Dispatcher_hpp
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#define Dispatcher_hpp
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#include <algorithm>
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#include <cstdint>
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namespace Reflection {
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/*!
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Calls @c t.dispatch<c>(args...) as efficiently as possible.
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*/
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template <typename TargetT, typename... Args> void dispatch(TargetT &t, uint8_t c, Args &&... args) {
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#define Opt(x) case x: t.template dispatch<x>(std::forward<Args>(args)...); break
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#define Opt4(x) Opt(x + 0x00); Opt(x + 0x01); Opt(x + 0x02); Opt(x + 0x03)
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#define Opt16(x) Opt4(x + 0x00); Opt4(x + 0x04); Opt4(x + 0x08); Opt4(x + 0x0c)
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#define Opt64(x) Opt16(x + 0x00); Opt16(x + 0x10); Opt16(x + 0x20); Opt16(x + 0x30)
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#define Opt256(x) Opt64(x + 0x00); Opt64(x + 0x40); Opt64(x + 0x80); Opt64(x + 0xc0)
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switch(c) {
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Opt256(0);
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}
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#undef Opt256
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#undef Opt64
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#undef Opt16
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#undef Opt4
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#undef Opt
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}
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// Yes, macros, yuck. But I want an actual switch statement for the dispatch to start
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// and to allow a simple [[fallthrough]] through all subsequent steps up until end.
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// So I don't think I have much in the way of options here.
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//
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// Sensible choices by the optimiser are assumed.
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#define index2(n) index(n); index(n+1);
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#define index4(n) index2(n); index2(n+2);
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#define index8(n) index4(n); index4(n+4);
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#define index16(n) index8(n); index8(n+8);
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#define index32(n) index16(n); index16(n+16);
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#define index64(n) index32(n); index32(n+32);
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#define index128(n) index64(n); index64(n+64);
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#define index256(n) index128(n); index128(n+128);
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#define index512(n) index256(n); index256(n+256);
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#define index1024(n) index512(n); index512(n+512);
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#define index2048(n) index1024(n); index1024(n+1024);
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#define switch_indices(x) switch(x) { default: assert(false); index2048(0); }
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static constexpr int switch_max = 2048;
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/// Provides glue for a run of calls like:
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///
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/// SequencerT.perform<0>(...)
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/// SequencerT.perform<1>(...)
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/// SequencerT.perform<2>(...)
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/// ...etc...
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///
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/// Allowing the caller to execute any subrange of the calls.
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template <typename SequencerT>
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struct RangeDispatcher {
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static_assert(SequencerT::max < switch_max);
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/// Perform @c target.perform<n>() for the input range `begin <= n < end`.
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template <typename... Args>
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static void dispatch(SequencerT &target, int begin, int end, Args&&... args) {
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// Minor optimisation: do a comparison with end once outside the loop and if it implies so
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// then do no further comparisons within the loop. This is somewhat targetted at expected
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// use cases.
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if(end < SequencerT::max) {
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dispatch<true>(target, begin, end, args...);
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} else {
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dispatch<false>(target, begin, end, args...);
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}
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}
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private:
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template <bool use_end, typename... Args> static void dispatch(SequencerT &target, int begin, int end, Args&&... args) {
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#define index(n) \
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case n: \
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if constexpr (n <= SequencerT::max) { \
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if constexpr (n == SequencerT::max) return; \
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if constexpr (n < SequencerT::max) { \
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if(use_end && end == n) return; \
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} \
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target.template perform<n>(args...); \
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} \
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[[fallthrough]];
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switch_indices(begin);
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#undef index
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}
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};
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/// Uses a classifier to divide a range into typed subranges and issues calls to a target of the form:
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///
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/// * begin<type>(location) upon entering a new region;
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/// * end<type>(location) upon entering a region; and
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/// * advance<type>(distance) in as many chunks as required to populate the inside of the region.
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///
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/// @c begin and @c end have iterator-style semantics: begin's location will be the first location in the relevant subrange and
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/// end's will be the first location not in the relevant subrange.
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template <typename ClassifierT, typename TargetT>
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struct SubrangeDispatcher {
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static_assert(ClassifierT::max < switch_max);
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static void dispatch(TargetT &target, int begin, int end) {
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#define index(n) \
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case n: \
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if constexpr (n <= ClassifierT::max) { \
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constexpr auto region = ClassifierT::region(n); \
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if constexpr (n == find_begin(n)) { \
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if(n >= end) { \
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return; \
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} \
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target.template begin<region>(n); \
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} \
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if constexpr (n == find_end(n) - 1) { \
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const auto clipped_begin = std::max(begin, find_begin(n)); \
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const auto clipped_end = std::min(end, find_end(n)); \
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target.template advance<region>(clipped_end - clipped_begin); \
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\
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if(clipped_end == n + 1) { \
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target.template end<region>(n + 1); \
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} \
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} \
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} \
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[[fallthrough]];
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switch_indices(begin);
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#undef index
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}
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private:
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static constexpr int find_begin(int n) {
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const auto type = ClassifierT::region(n);
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while(n && ClassifierT::region(n - 1) == type) --n;
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return n;
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}
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static constexpr int find_end(int n) {
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const auto type = ClassifierT::region(n);
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while(n < ClassifierT::max && ClassifierT::region(n) == type) ++n;
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return n;
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}
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};
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#undef switch_indices
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#undef index2
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#undef index4
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#undef index8
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#undef index16
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#undef index32
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#undef index64
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#undef index128
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#undef index256
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#undef index512
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#undef index1024
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#undef index2048
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}
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#endif /* Dispatcher_hpp */
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