@printf: significant digits in floating point representation

General Usage
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10

Fyi, you might want to check out this MATLAB solution.

Below is a simplified Julia version that produces the desired output:

using Printf

function str_significant(x::Float64, sigdig::Int)
    (x == 0) && (return "0")
    x = round(x, sigdigits=sigdig)
    n = length(@sprintf("%d", abs(x)))              # length of the integer part
    if (x ≤ -1 || x ≥ 1)
        decimals = max(sigdig - n, 0)               # 'sig - n' decimals needed 
    else
        Nzeros = ceil(Int, -log10(abs(x))) - 1      # No. zeros after decimal point before first number
        decimals = sigdig + Nzeros
    end 
    return @sprintf("%.*f", decimals, x)
end

str_significant(.000012340000, 2)                   # 0.000012
str_significant(.123400000000, 2)                   # 0.12
str_significant(1.234, 2)                           # 1.2
str_significant(1234000.000, 2)                     # 1200000