julia> nextfloat(0.)
5.0e-324

julia> prevfloat(0.)
NaN

julia> z = BigFloat(0.)
0e+00 with 256 bits of precision

julia> nextfloat(z)
2.382564904887951073216169781732674520415196125559239787955023752600945386104324e-323228497 with 256 bits of precision

julia> prevfloat(z)
-2.382564904887951073216169781732674520415196125559239787955023752600945386104324e-323228497 with 256 bits of precision

julia> nextfloat(-1.)
-1.0000000000000002

julia> prevfloat(-1.)
-0.9999999999999999

julia> z = BigFloat(-1.)
-1e+00 with 256 bits of precision

julia> nextfloat(z)
-9.999999999999999999999999999999999999999999999999999999999999999999999999999914e-01 with 256 bits of precision

julia> prevfloat(z)
-1.000000000000000000000000000000000000000000000000000000000000000000000000000017e+00 with 256 bits of precision