a way to check for nearest neighbor with bit ops and xor sets with mash

iter_by_trail_zeros.txt

>>> bin(8)
'0b1000'
>>> bin(12)
'0b1100'
>>> bin(16)
'0b10000'
>>> bin(16 + 0b100)
'0b10100'
>>> bin(16 + 0b100 + 0b100)
'0b11000'
>>> bin(16 + 0b100 + 0b100 + 0b100)
'0b11100'

submask_down.txt

>>> s = 0b10110010
>>> mask = 0b10110010
>>> k = 0b10011
>>> bin(s & k)
'0b10010'
>>> start = s & k
>>> start
18
>>> start = (start - 1) & mask
>>> start
16
>>> bin(start)
'0b10000'
>>> start = (start - 1) & mask
>>> bin(start)
'0b10'
>>> start = (start - 1) & mask
>>> bin(start)
'0b0'

submask_neighbor_search.txt

>>> s = 0b10110010
>>> s
178
>>> mask = 0b10110010
>>> s = (s - 1) & mask
>>> s
176
>>> bin(s)
'0b10110000'
>>> s = (s - 1) & mask
>>> bin(s)
'0b10100010'
>>> s
162
>>> s = (s - 1) & mask
>>> bin(s)
'0b10100000'
>>> s
160
>>> s = (s - 1) & mask
>>> bin(s)
'0b10010010'
>>> s
146

submask_up.txt

>>> s = 0b101100
>>> 0b1000 - 0b100
4
>>> 0b100 + 4
8
>>> mask = 0b101100
>>> d = 0b1000
>>> d = (d - 1) & mask
>>> d
4
>>> bin(d)
'0b100'
>>> d = 0b1100
>>> bin(d)
'0b1100'
>>> d = (d - 1) & mask
>>> bin(d)
'0b1000'
>>> d = (d - 1) & mask
>>> bin(d)
'0b100'
>>> 0b101100
44
>>> d = 0b101100
>>> d = (d - 1) & mask
>>> bin(d)
'0b101000'
>>> d = (d - 1) & mask
>>> bin(d)
'0b100100'
>>> d = (d - 1) & mask
>>> bin(d)
'0b100000'
>>> d = (d - 1) & mask
>>> bin(d)
'0b1100'

submasks.cpp

void iterate_submasks(uint8_t mask) {
    // Start from the mask itself, then decrease
    for (uint8_t sub = mask; sub; sub = (sub - 1) & mask) {
        printf("0b");
        for (int i = 7; i >= 0; --i) {
            printf("%d", (sub >> i) & 1);
        }
        printf("\n");
    }
}