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Implement bit flipping with a lookup table

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Should improve performance.
This version is cooler, and also does not suffer from iteration limits
This commit is contained in:
ISSOtm
2022-05-21 12:57:46 +02:00
committed by Eldred Habert
parent b4dadd35b6
commit 7a7126f3b8
3 changed files with 19 additions and 11 deletions
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20
include/gfx/main.hpp
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@@ -13,6 +13,7 @@
#include <limits.h>
#include <stdint.h>
#include <string>
#include <utility>
#include <vector>
#include "helpers.h"
@@ -87,12 +88,19 @@ struct Palette {
uint8_t size() const;
};
static constexpr uint8_t flip(uint8_t byte) {
// To flip all the bits, we'll flip both nibbles, then each nibble half, etc.
byte = (byte & 0b0000'1111) << 4 | (byte & 0b1111'0000) >> 4;
byte = (byte & 0b0011'0011) << 2 | (byte & 0b1100'1100) >> 2;
byte = (byte & 0b0101'0101) << 1 | (byte & 0b1010'1010) >> 1;
return byte;
namespace detail {
template<typename T, T... i>
static constexpr auto flipTable(std::integer_sequence<T, i...>) {
return std::array{[](uint8_t byte) {
// To flip all the bits, we'll flip both nibbles, then each nibble half, etc.
byte = (byte & 0b0000'1111) << 4 | (byte & 0b1111'0000) >> 4;
byte = (byte & 0b0011'0011) << 2 | (byte & 0b1100'1100) >> 2;
byte = (byte & 0b0101'0101) << 1 | (byte & 0b1010'1010) >> 1;
return byte;
}(i)...};
}
}
// Flipping tends to happen fairly often, so take a bite out of dcache to speed it up
static constexpr auto flipTable = detail::flipTable(std::make_integer_sequence<uint16_t, 256>());
#endif /* RGBDS_GFX_MAIN_HPP */

6
src/gfx/process.cpp
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@@ -652,7 +652,7 @@ public:
// Count the line itself as mirrorred; vertical mirroring is
// already taken care of because the symmetric line will be XOR'd
// the same way. (...which is a problem, but probably benign.)
_hash ^= flip(bitplanes >> 8) << 8 | flip(bitplanes & 0xFF);
_hash ^= flipTable[bitplanes >> 8] << 8 | flipTable[bitplanes & 0xFF];
}
}
}
@@ -680,7 +680,7 @@ public:
// Check if we have horizontal mirroring, which scans the array forward again
if (std::equal(_data.begin(), _data.end(), other._data.begin(),
[](uint8_t lhs, uint8_t rhs) { return lhs == flip(rhs); })) {
[](uint8_t lhs, uint8_t rhs) { return lhs == flipTable[rhs]; })) {
return MatchType::HFLIP;
}
@@ -694,7 +694,7 @@ public:
if (lhs != rhs) {
hasVFlip = false;
}
if (lhs != flip(rhs)) {
if (lhs != flipTable[rhs]) {
hasVHFlip = false;
}
if (!hasVFlip && !hasVHFlip) {

4
src/gfx/reverse.cpp
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@@ -271,8 +271,8 @@ void reverse() {
uint8_t realY = attribute & 0x40 ? 7 - y : y;
uint8_t bitplane0 = tileData[realY * 2], bitplane1 = tileData[realY * 2 + 1];
if (attribute & 0x20) { // Handle horizontal flip
bitplane0 = flip(bitplane0);
bitplane1 = flip(bitplane1);
bitplane0 = flipTable[bitplane0];
bitplane1 = flipTable[bitplane1];
}
uint8_t *ptr = &rowPtrs[y][tx * 8 * SIZEOF_PIXEL];
for (uint8_t x = 0; x < 8; ++x) {