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Slightly smarter: this does branchless shadowing without additional storage.

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This commit is contained in:
Thomas Harte 2021-02-24 18:46:41 -05:00
parent 71a107fe75
commit 55c9d152e9
1 changed files with 10 additions and 12 deletions
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22
Machines/Apple/AppleIIgs/MemoryMap.hpp
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@ -27,6 +27,7 @@ class MemoryMap {
void set_storage(std::vector<uint8_t> &ram, std::vector<uint8_t> &rom) {
// Keep a pointer for later; also note the proper RAM offset.
ram_base = ram.data();
shadow_base[0] = ram_base; // i.e. all unshadowed writes go to where they've already gone (to make a no-op).
shadow_base[1] = &ram[ram.size() - 0x02'0000]; // i.e. all shadowed writes go somewhere in the last
// 128bk of RAM.
@ -435,11 +436,11 @@ class MemoryMap {
// Disables shadowing for the region starting from @c zone if @c flag is true;
// otherwise enables it.
#define apply(flag, zone) \
if(flag) { \
#define apply(disable, zone) \
if(disable) { \
regions[region_map[zone]].flags &= ~Region::IsShadowed; \
} else { \
regions[region_map[zone]].flags |= Region::IsShadowed; \
} else { \
regions[region_map[zone]].flags |= Region::IsShadowed; \
}
// Relevant bits:
@ -457,8 +458,8 @@ class MemoryMap {
// Text Page 1, main and auxiliary — $0400–$0800.
apply(shadow_register_ & 0x01, 0x0004);
apply(shadow_register_ & 0x01, 0x0104);
apply((shadow_register_ & 0x01) || inhibit_all_pages, 0x0204); // All other pages uses the same shadowing flags.
apply((shadow_register_ & 0x01) || inhibit_all_pages, 0x0304);
// apply((shadow_register_ & 0x01) || inhibit_all_pages, 0x0204); // All other pages uses the same shadowing flags.
// apply((shadow_register_ & 0x01) || inhibit_all_pages, 0x0304);
assert_is_region(0x004, 0x008);
assert_is_region(0x104, 0x108);
assert_is_region(0x204, 0x208);
@ -565,9 +566,6 @@ class MemoryMap {
set_shadowing();
}
// Throwaway storage to facilitate branchless handling of shadowing.
uint8_t shadow_throwaway_;
#undef assert_is_region
public:
@ -579,8 +577,8 @@ class MemoryMap {
// reduces what would otherwise be a 1.25mb table down to not a great deal more than 64kb.
std::array<uint8_t, 65536> region_map{};
uint8_t *ram_base = nullptr;
uint8_t *shadow_base[2] = {&shadow_throwaway_, nullptr};
static constexpr int shadow_mask[2] = {0, 0x01'ffff};
uint8_t *shadow_base[2] = {nullptr, nullptr};
static constexpr int shadow_mask[2] = {0xff'ffff, 0x01'ffff};
struct Region {
uint8_t *write = nullptr;
@ -607,7 +605,7 @@ class MemoryMap {
#define MemoryMapWrite(map, region, address, value) \
if(region.write) { \
region.write[address] = *value; \
const bool is_shadowed = region.flags & MemoryMap::Region::IsShadowed; \
const auto is_shadowed = region.flags & MemoryMap::Region::IsShadowed; \
map.shadow_base[is_shadowed][(&region.write[address] - map.ram_base) & map.shadow_mask[is_shadowed]] = *value; \
}