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Subject: Q: type matching with IEEE 754 double and Intel endianess
From: gautier_niouzes@hotmail.com
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Date: 2012-12-07T00:54:26-08:00
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Hello,

For a software component (Excel Writer), I have a portable way of getting a binary output for a Long_Float, by using Dmitry's IEEE_754 package.
It is working perfectly fine (see IEEE_Double_Intel_Portable function below).

Now, assume the program is running on a machine where Long_Float is actually IEEE_754, and endianess is the Intel one.
Is there a "solid" way to prove with some check that it is the case ?
Then a rough type conversion would be sufficient (e.g. IEEE_Double_Intel_Native below). The only advantage of the latter is that it is faster.

Cheers
G.


  function IEEE_Double_Intel_Portable(x: Long_Float) return Byte_buffer is
    pragma Inline(IEEE_Double_Intel_Portable);
    d : Byte_buffer(1..8);
    --
    use IEEE_754.Long_Floats;
    f64: constant Float_64:= To_IEEE(x);
  begin
    for i in d'Range loop
      d(i):= f64(9-i); -- Order is reversed
    end loop;
    return d;
  end IEEE_Double_Intel_Portable;

  function IEEE_Double_Intel_Native(x: Long_Float) return Byte_buffer is
    pragma Inline(IEEE_Double_Intel_Native);
    d : Byte_buffer(1..8);
    for d'Address use x'Address;
    pragma Import (Ada, d);
  begin
    return d;
  end IEEE_Double_Intel_Native;