Please explain glsl expressions

[tigrazone]

Hello!
What do this

SparseVoxelOctree/shader/quad.vert

Line 2 in 3b175fc

void main() { gl_Position = vec4(vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2) * 2.0 - 1.0, 0.0, 1.0); }

and this piesces of code

SparseVoxelOctree/shader/sobol.comp

Line 83 in 3b175fc

c = findLSB(~(uSobol[uDimension]++));

i.e. "find lsb of 'not' of..."
Why LSB? Why 'not'?