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CLK/Reflection/Dispatcher.hpp
2023-06-13 15:25:51 -04:00

175 lines
5.3 KiB
C++

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