What would be the recommended way of getting the base 10 mantissa and exponent of a floating point number? Is there a package that does this? Or should I just reparse from printed representation, as in using Printf function get_mantissa_exponent(x) str = @sprintf "%.15e" x # specialize 15 …

[image] Tamas_Papp: What would be the recommended way of getting the base 10 mantissa and exponent of a floating point number? It depends on what you mean by “the” base-10 mantissa and exponent. I assume you are mainly interested in binary floating-point types like Float64 and Float32. The …

Thanks! Sorry for not being clear, yes, I am after the printed approximation.

[image] Tamas_Papp: julia> get_mantissa_exponent(3.17) (mantissa = "3170000000000000", exponent = 0) Is this the result you expected? Based on the title, I would have expected mantissa 317 and exponent -2 (or an equivalent alternative like 3170 and -3) because 317 * 10^-2 = 3.17. Coincidenta…

[image] barucden: Is this the result you expected? Technically you are right, but I am after a string which I can just cut off at some point and insert a decimal dot, so I am flexible. The point of the exercise is for printing, into LaTeX. That is, I want to generate output like raw"$4.92 \c…

How about a simplistic regex? julia> replace(string((10rand())^10), r"(\d+.\d+)[ef]\+?(-?\d+)"=>s"$\1 \\cdot 10^{\2}$") |> println $6.71626435914464 \cdot 10^{6}$

This works for positive floating point number. Just check if number is negative and manually insert a negative sign yourself. julia> a = log(10, Float64(π) ) 0.4971498726941338 julia> println("$(10.0^(a-trunc(a))) * 10^$(Int64(trunc(a)))") 3.1415926535897927 * 10^0 julia> a = log(10, 123…

Doing something with a numeric log is highly likely to have catastrophic rounding problems around powers of 10. In my view, the best answer in this case is to use standard tooling (like @sprintf) and fix it up as strings — either as a split like Tamas first suggested or with a regex. Both are real…

I don’t think the original poster cares about rounding errors. He said “Thanks! Sorry for not being clear, yes, I am after the printed approximation.” I take that to mean approximation in base 10 (not approximation in base 2)

The problem I was worried about isn’t small errors. I suspect that it’s possible the exponent and mantissa might round different ways. Around powers of 10 that could easily lead to a factor of 10 error — something that I suspect everyone would care about. I might be wrong — and I think you might be…

Get base10 mantissa and exponent of real (eg Float64)

General Usage

rafael.guerra October 21, 2024, 2:12pm 7

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Get base10 mantissa and exponent of real (eg Float64)

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