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Unrolls the loops for slightly fewer conditionals.

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This commit is contained in:
Thomas Harte 2018-06-03 07:27:03 -04:00
parent d84b8700a3
commit d380595ad4
2 changed files with 29 additions and 33 deletions
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15
Machines/AppleII/Video.cpp
View File

@ -57,19 +57,4 @@ void VideoBase::set_high_resolution() {
void VideoBase::set_character_rom(const std::vector<uint8_t> &character_rom) {
character_rom_ = character_rom;
// Bytes in the character ROM are stored in reverse bit order. Reverse them
// ahead of time so as to be able to use the same scaling table as for
// high-resolution graphics.
for(auto &byte : character_rom_) {
byte =
((byte & 0x40) ? 0x01 : 0x00) |
((byte & 0x20) ? 0x02 : 0x00) |
((byte & 0x10) ? 0x04 : 0x00) |
((byte & 0x08) ? 0x08 : 0x00) |
((byte & 0x04) ? 0x10 : 0x00) |
((byte & 0x02) ? 0x20 : 0x00) |
((byte & 0x01) ? 0x40 : 0x00) |
(byte & 0x80);
}
}

47
Machines/AppleII/Video.hpp
View File

@ -130,11 +130,14 @@ template <class BusHandler> class Video: public VideoBase {
const uint8_t character_pattern = character_rom_[character_address] ^ inverses[character >> 6];
int mask = 0x01;
for(int p = 0; p < 7; ++p) {
pixel_pointer_[p] = character_pattern & mask;
mask <<= 1;
}
// The character ROM is output MSB to LSB rather than LSB to MSB.
pixel_pointer_[0] = character_pattern & 0x40;
pixel_pointer_[1] = character_pattern & 0x20;
pixel_pointer_[2] = character_pattern & 0x10;
pixel_pointer_[3] = character_pattern & 0x08;
pixel_pointer_[4] = character_pattern & 0x04;
pixel_pointer_[5] = character_pattern & 0x02;
pixel_pointer_[6] = character_pattern & 0x01;
graphics_carry_ = character_pattern & 0x40;
pixel_pointer_ += 7;
}
@ -142,9 +145,12 @@ template <class BusHandler> class Video: public VideoBase {
case GraphicsMode::LowRes: {
const int row_shift = (row_&4);
// TODO: decompose into two loops, possibly.
for(int c = column_; c < pixel_end; ++c) {
const uint8_t nibble = (bus_handler_.perform_read(static_cast<uint16_t>(text_address + c)) >> row_shift) & 0x0f;
// Low-resolution graphics mode shifts the colour code on a loop, but has to account for whether this
// 14-sample output window is starting at the beginning of a colour cycle or halfway through.
if(c&1) {
pixel_pointer_[0] = pixel_pointer_[4] = pixel_pointer_[8] = pixel_pointer_[12] = nibble & 4;
pixel_pointer_[1] = pixel_pointer_[5] = pixel_pointer_[9] = pixel_pointer_[13] = nibble & 8;
@ -167,23 +173,28 @@ template <class BusHandler> class Video: public VideoBase {
for(int c = column_; c < pixel_end; ++c) {
const uint8_t graphic = bus_handler_.perform_read(static_cast<uint16_t>(graphics_address + c));
// High resolution graphics shift out LSB to MSB, optionally with a delay of half a pixel.
// If there is a delay, the previous output level is held to bridge the gap.
if(graphic & 0x80) {
pixel_pointer_[0] = graphics_carry_;
pixel_pointer_++;
}
int mask = 0x01;
for(int p = 0; p < 12; p += 2) {
pixel_pointer_[p] = graphic & mask;
pixel_pointer_[p+1] = graphic & mask;
mask <<= 1;
}
pixel_pointer_[12] = graphic & 0x40;
pixel_pointer_ += 13;
if(!(graphic & 0x80)) {
pixel_pointer_[0] = graphic & 0x40;
pixel_pointer_++;
pixel_pointer_[1] = pixel_pointer_[2] = graphic & 0x01;
pixel_pointer_[3] = pixel_pointer_[4] = graphic & 0x02;
pixel_pointer_[5] = pixel_pointer_[6] = graphic & 0x04;
pixel_pointer_[7] = pixel_pointer_[8] = graphic & 0x08;
pixel_pointer_[9] = pixel_pointer_[10] = graphic & 0x10;
pixel_pointer_[11] = pixel_pointer_[12] = graphic & 0x20;
pixel_pointer_[13] = graphic & 0x40;
} else {
pixel_pointer_[0] = pixel_pointer_[1] = graphic & 0x01;
pixel_pointer_[2] = pixel_pointer_[3] = graphic & 0x02;
pixel_pointer_[4] = pixel_pointer_[5] = graphic & 0x04;
pixel_pointer_[6] = pixel_pointer_[7] = graphic & 0x08;
pixel_pointer_[8] = pixel_pointer_[9] = graphic & 0x10;
pixel_pointer_[10] = pixel_pointer_[11] = graphic & 0x20;
pixel_pointer_[12] = pixel_pointer_[13] = graphic & 0x40;
}
graphics_carry_ = graphic & 0x40;
pixel_pointer_ += 14;
}
} break;
}