backtracking alternative

[ethers]

1 idea is to use "roundness"

the "roundness" of a number is the largest power of 2 such that B % roundness = 0
6 has roundness 2
96 has roundness 32
basically it's the largest power of 2 that divides it

lets say you want to go from 117 to 1
you'd go 117[1] 116[4] 112[16] 96[32] 64...... 64 is special because it can't go 'up' any further, so maybe 64 just goes back half way to 32

for power of 2 one idea is go back halfway
if need to go up again, say we want 50, just restart back at 64 and backtrack one