dec2Eng.lua

-- scriptName: dec2Eng
-- by: dkh503@gmail.com

-- Enter a number and get the Engineering Notation.

function dec2Eng(x)
    assert(tonumber(x), "Error: invalid entry.")
    y = 0

    while x >= 1 do
        x = x / 10
        y = y + 1
    end
    while x < 1 do
        x = x * 10
        y = y - 1
    end

    if (y % 3) == 1 then
        y = y - 1
        x = x * 10
    elseif (y % 3) == 2 then
        y = y + 1
        x = x / 10
    end

    if x < 1 then
        x = x * 1000
        y = y - 3
    end

    return string.format("%.3fe%d", x, y)
end

io.write(
[[----------------------------------
 ** dec2Eng.lua **
Converts decimal, hex or
scientific notation entries to
Engineering Notation
----------------------------------]])

io.write("\nEnter a number      : ")
z = dec2Eng(io.read("*n"))

io.write(string.format("Engineering Notation: %s\n\n", z))



-- Engineering notation:
-- 1. Uses exponents in multiples of 3 only.
-- 2. 0 < Base <1000

-- This matches up with "Metric Prefixes" like milli[amps],
-- micro[meters], and nano[farads] (negative exponents);
-- and kilo[ohms], mega[hertz], and giga[bytes] (positive exponents),
-- often seen in electronic and engineering measurements.

--[[https://en.wikipedia.org/wiki/Metric_prefix

    Tera    T   1000000000000   10e12
    Giga    G   1000000000  10e9
    Mega    M   1000000     10e6
    Kilo    K   1000        10e3
    (none)  (none)  1       10e0
    milli   m   0.001       10e-3
    micro   µ  0.000001    10e-6
    nano    n   0.000000001     10e-9
    pico    p   0.000000000001  10e-12

--]]