_nearest_representable_edf_time_value isn't quite right

[ericphanson]

EDF.jl/src/types.jl

Lines 117 to 121 in 2eef49f

	_nearest_representable_edf_time_value(::Nothing) = nothing
	function _nearest_representable_edf_time_value(x)
	return round(x; digits=(8 - (ndigits(floor(Int, x)) + signbit(x) + isinteger(x))))
	end

First- I don't think we need this for onsets and annotations, xref #75, #72). But I think it is useful to have, at least for folks doing the encoding (which are EDF.jl's users but not EDF.jl itself). However, it should be:

function _nearest_representable_edf_time_value(x, rm::RoundingMode=RoundNearest)
    return round(x, rm; digits=(8 - (ndigits(floor(Int, x)) + signbit(x) + !isinteger(x))))
end

where I've added an optional rounding mode. The difference here is !isinteger - we lose a digit when we have to write the decimal.

Running

using Printf
function edf_roundtrip(x::Real)
    result = missing
    if isinteger(x)
        str = string(trunc(Int, x))
        if length(str) <= 8
            result = str
        end
    else
        fpart, ipart = modf(x)
        ipart_str = string('-'^signbit(x), Int(abs(ipart))) # handles `-0.0` case
        fpart_str = @sprintf "%.7f" abs(fpart)
        fpart_str = fpart_str[3:end] # remove leading `0.`
        if length(ipart_str) < 7
            result = ipart_str * '.' * fpart_str[1:(7-length(ipart_str))]
        elseif length(ipart_str) <= 8
            result = ipart_str
        end
    end
    if !ismissing(result)
        return parse(Float64, result)
    end
    error("failed to fit header field into EDF's 8 ASCII character limit. Got: $x")
    return nothing
end

edf_roundtrip_error(x) = abs(x - edf_roundtrip(x))

function _nearest_representable_edf_time_value(x, rm::RoundingMode=RoundNearest)
    return round(x, rm; digits=(8 - (ndigits(floor(Int, x)) + signbit(x) + !isinteger(x))))
end

f = x -> edf_roundtrip_error(_nearest_representable_edf_time_value(x))
lines(xs, f.(xs))

which modifies the _edf_repr code for use here, I get

whereas if I remove the ! to match the current code, I get