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Remove a conditional from the hot path.

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This commit is contained in:
Thomas Harte 2024-04-29 22:16:06 -04:00
parent 5a84e98256
commit c7747ec5a0
1 changed files with 7 additions and 8 deletions
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15
Machines/Acorn/Archimedes/MemoryController.hpp
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@ -135,7 +135,7 @@ struct MemoryController {
case Zone::LogicallyMappedRAM: { case Zone::LogicallyMappedRAM: {
const auto item = logical_ram<IntT, false>(address, trans); const auto item = logical_ram<IntT, false>(address, trans);
if(!item) { if(item < reinterpret_cast<IntT *>(ram_.data())) {
return false; return false;
} }
*item = source; *item = source;
@ -182,7 +182,7 @@ struct MemoryController {
case Zone::LogicallyMappedRAM: { case Zone::LogicallyMappedRAM: {
const auto item = logical_ram<IntT, true>(address, trans); const auto item = logical_ram<IntT, true>(address, trans);
if(!item) { if(item < reinterpret_cast<IntT *>(ram_.data())) {
return false; return false;
} }
source = *item; source = *item;
@ -276,8 +276,8 @@ struct MemoryController {
} }
bool has_moved_rom_ = false; bool has_moved_rom_ = false;
std::array<uint8_t, 4*1024*1024> ram_{};
std::array<uint8_t, 2*1024*1024> rom_; std::array<uint8_t, 2*1024*1024> rom_;
std::array<uint8_t, 4*1024*1024> ram_{};
InputOutputController<InterruptObserverT, ClockRateObserverT> ioc_; InputOutputController<InterruptObserverT, ClockRateObserverT> ioc_;
template <typename IntT> template <typename IntT>
@ -353,6 +353,7 @@ struct MemoryController {
bool map_dirty_ = true; bool map_dirty_ = true;
/// @returns A pointer to somewhere in @c ram_ if RAM is mapped to this area, or a pointer to somewhere lower than @c ram_.data() otherwise.
template <typename IntT, bool is_read> template <typename IntT, bool is_read>
IntT *logical_ram(uint32_t address, bool trans) { IntT *logical_ram(uint32_t address, bool trans) {
// Possibly TODO: this recompute-if-dirty flag is supposed to ameliorate for an expensive // Possibly TODO: this recompute-if-dirty flag is supposed to ameliorate for an expensive
@ -366,10 +367,6 @@ struct MemoryController {
const size_t page = address >> page_address_shift_; const size_t page = address >> page_address_shift_;
const auto &map = mapping<is_read>(trans, os_mode_); const auto &map = mapping<is_read>(trans, os_mode_);
if(!map[page]) {
return nullptr;
}
address &= page_adddress_mask_; address &= page_adddress_mask_;
return reinterpret_cast<IntT *>(&map[page][address]); return reinterpret_cast<IntT *>(&map[page][address]);
} }
@ -389,7 +386,9 @@ struct MemoryController {
void update_mapping() { void update_mapping() {
// Clear all logical mappings. // Clear all logical mappings.
for(auto &map: mapping_) { for(auto &map: mapping_) {
std::fill(map.begin(), map.end(), nullptr); // Seed all pointers to an address sufficiently far lower than the beginning of RAM as to mark
// the entire page as unmapped no matter what offset is added.
std::fill(map.begin(), map.end(), ram_.data() - 32768);
} }
// For each physical page, project it into logical space // For each physical page, project it into logical space