mirror of https://github.com/OpenTTD/OpenTTD.git
Codechange: replace hand written function to find first/last bit with C++ variant
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@ -22,59 +22,3 @@ const uint8_t _ffb_64[64] = {
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4, 0, 1, 0, 2, 0, 1, 0,
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3, 0, 1, 0, 2, 0, 1, 0,
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};
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/**
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* Search the first set bit in a 64 bit variable.
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*
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* This algorithm is a static implementation of a log
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* congruence search algorithm. It checks the first half
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* if there is a bit set search there further. And this
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* way further. If no bit is set return 0.
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*
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* @param x The value to search
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* @return The position of the first bit set
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*/
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uint8_t FindFirstBit(uint64_t x)
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{
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if (x == 0) return 0;
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/* The macro FIND_FIRST_BIT is better to use when your x is
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not more than 128. */
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uint8_t pos = 0;
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if ((x & 0xffffffffULL) == 0) { x >>= 32; pos += 32; }
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if ((x & 0x0000ffffULL) == 0) { x >>= 16; pos += 16; }
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if ((x & 0x000000ffULL) == 0) { x >>= 8; pos += 8; }
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if ((x & 0x0000000fULL) == 0) { x >>= 4; pos += 4; }
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if ((x & 0x00000003ULL) == 0) { x >>= 2; pos += 2; }
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if ((x & 0x00000001ULL) == 0) { pos += 1; }
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return pos;
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}
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/**
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* Search the last set bit in a 64 bit variable.
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*
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* This algorithm is a static implementation of a log
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* congruence search algorithm. It checks the second half
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* if there is a bit set search there further. And this
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* way further. If no bit is set return 0.
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*
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* @param x The value to search
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* @return The position of the last bit set
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*/
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uint8_t FindLastBit(uint64_t x)
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{
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if (x == 0) return 0;
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uint8_t pos = 0;
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if ((x & 0xffffffff00000000ULL) != 0) { x >>= 32; pos += 32; }
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if ((x & 0x00000000ffff0000ULL) != 0) { x >>= 16; pos += 16; }
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if ((x & 0x000000000000ff00ULL) != 0) { x >>= 8; pos += 8; }
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if ((x & 0x00000000000000f0ULL) != 0) { x >>= 4; pos += 4; }
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if ((x & 0x000000000000000cULL) != 0) { x >>= 2; pos += 2; }
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if ((x & 0x0000000000000002ULL) != 0) { pos += 1; }
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return pos;
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}
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@ -222,8 +222,35 @@ inline uint8_t FindFirstBit2x64(const int value)
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}
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}
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uint8_t FindFirstBit(uint64_t x);
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uint8_t FindLastBit(uint64_t x);
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/**
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* Search the first set bit in a value.
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* When no bit is set, it returns 0.
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*
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* @param x The value to search.
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* @return The position of the first bit set.
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*/
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template <typename T>
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constexpr uint8_t FindFirstBit(T x)
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{
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if (x == 0) return 0;
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return std::countr_zero(x);
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}
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/**
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* Search the last set bit in a value.
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* When no bit is set, it returns 0.
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*
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* @param x The value to search.
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* @return The position of the last bit set.
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*/
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template <typename T>
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constexpr uint8_t FindLastBit(T x)
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{
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if (x == 0) return 0;
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return std::numeric_limits<T>::digits - std::countl_zero(x) - 1;
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}
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/**
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* Clear the first bit in an integer.
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@ -440,7 +440,7 @@ protected:
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* integer, so at about 31 bits because of the sign bit, the
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* least significant bits are removed.
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*/
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int mult_range = FindLastBit(x_axis_offset) + FindLastBit(abs(datapoint));
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int mult_range = FindLastBit<uint32_t>(x_axis_offset) + FindLastBit<uint64_t>(abs(datapoint));
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int reduce_range = std::max(mult_range - 31, 0);
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/* Handle negative values differently (don't shift sign) */
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@ -309,7 +309,7 @@ static SigFlags ExploreSegment(Owner owner)
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Track track = TrackBitsToTrack(tracks_masked); // mask TRACK_BIT_X and Y too
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if (HasSignalOnTrack(tile, track)) { // now check whole track, not trackdir
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SignalType sig = GetSignalType(tile, track);
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Trackdir trackdir = (Trackdir)FindFirstBit((tracks * 0x101) & _enterdir_to_trackdirbits[enterdir]);
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Trackdir trackdir = (Trackdir)FindFirstBit((tracks * 0x101U) & _enterdir_to_trackdirbits[enterdir]);
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Trackdir reversedir = ReverseTrackdir(trackdir);
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/* add (tile, reversetrackdir) to 'to-be-updated' set when there is
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* ANY conventional signal in REVERSE direction
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