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Eliminates modulus operation per ROM access.

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This commit is contained in:
Thomas Harte 2020-01-30 23:09:24 -05:00
parent f3db1a0c60
commit af976b8b3d
1 changed files with 4 additions and 1 deletions
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5
Machines/Atari/ST/AtariST.cpp
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@ -101,8 +101,10 @@ class ConcreteMachine:
const bool is_early_tos = true; const bool is_early_tos = true;
if(is_early_tos) { if(is_early_tos) {
rom_start_ = 0xfc0000;
for(c = 0xfc; c < 0xff; ++c) memory_map_[c] = BusDevice::ROM; for(c = 0xfc; c < 0xff; ++c) memory_map_[c] = BusDevice::ROM;
} else { } else {
rom_start_ = 0xe00000;
for(c = 0xe0; c < 0xe4; ++c) memory_map_[c] = BusDevice::ROM; for(c = 0xe0; c < 0xe4; ++c) memory_map_[c] = BusDevice::ROM;
} }
@ -245,7 +247,7 @@ class ConcreteMachine:
case BusDevice::ROM: case BusDevice::ROM:
memory = rom_.data(); memory = rom_.data();
address %= rom_.size(); address -= rom_start_;
break; break;
case BusDevice::Floating: case BusDevice::Floating:
@ -505,6 +507,7 @@ class ConcreteMachine:
std::vector<uint8_t> ram_; std::vector<uint8_t> ram_;
std::vector<uint8_t> rom_; std::vector<uint8_t> rom_;
uint32_t rom_start_ = 0;
enum class BusDevice { enum class BusDevice {
/// A mostly RAM page is one that returns ROM for the first 8 bytes, RAM elsewhere. /// A mostly RAM page is one that returns ROM for the first 8 bytes, RAM elsewhere.