little/big endian conversions

[lurker]

thank you all for your help!!

Bill Baxter Wrote:

> You don't necessarily need to put it into a byte array.  Just cast:
> 
>    void swap(ref byte a, ref byte b) {
>       byte tmp; tmp=a; a=b; b=tmp;
>    }
>    float f;
>    byte[4] fbytes = (cast(byte*)&f)[0..4];
>    swap(fbytes[0],fbytes[3]);
>    swap(fbytes[1],fbytes[2]);
>    float fswapped = *(cast(float*)fbytes.ptr);
> 
> Or instead of casts you can use a union.
> 
>      union FC { float f;      ubyte[4] c; }
>      FC fs;
>      fs.f = f;
>      swap(fs.c[0],fs.c[3]);
>      swap(fs.c[1],fs.c[2]);
>      float fswapped = fs.f;
> 
> --bb
> 
> lurker wrote:
> > so i need to put the float/double into an byte array and just swap?
> > 
> > Regan Heath Wrote:
> > 
> >> Bill Baxter wrote:
> >>> Regan Heath wrote:
> >>>> lurker wrote:
> >>>>> does anybody know how to convert float and doubles to little/big endian?
> >>>> This is a guess but if you read:
> >>>> http://en.wikipedia.org/wiki/IEEE_754
> >>>>
> >>>> You'll see the internal representation of a float, given that and a 
> >>>> little guess work I've come up with:
> >>>>
> >>>> import std.stdio;
> >>>>
> >>>> int extractSign(float f)
> >>>> {
> >>>>     return (*(cast(int*)&f) & 0x80000000) ? -1 : 1;
> >>>> }
> >>>>
> >>>> ubyte extractExp(float f)
> >>>> {
> >>>>     return (*(cast(int*)&f) << 1) & 0xFF000000;
> >>>> }
> >>>>
> >>>> int extractFraction(float f)
> >>>> {
> >>>>     return *(cast(int*)&f) & 0x007FFFFF;
> >>>> }
> >>>>
> >>>> void main()
> >>>> {
> >>>>     float f = -1.25f;
> >>>>         auto   sign     = extractSign(f);
> >>>>     auto   exp      = extractExp(f);
> >>>>     auto   fraction = extractFraction(f);
> >>>>         writefln(f);
> >>>>     writefln(sign);
> >>>>     writefln(exp);
> >>>>     writefln(fraction);   }
> >>>>
> >>>> which will extract the various parts of a float.
> >>>>
> >>>> Now, I have no idea how they might change on a big/little endian 
> >>>> system but I suspect each part would have it's byte order swapped.  In 
> >>>> which case, byte order swapping the extracted parts then re-assembling 
> >>>> might give you a byte order swapped float.
> >>>>
> >>>> Like I said, I'm guessing.
> >>>>
> >>>> What you want is 2 systems with different ordering and then you want 
> >>>> to dump the content of the float like this:
> >>>>
> >>>> writefln("%032b", *(cast(int*)&f));
> >>>>
> >>>> then compare.
> >>>>
> >>>> Regan
> >>>
> >>> It doesn't matter that it's in IEEE 745 format.  You just swap the bytes 
> >>> like it was any old kind of data.
> >> Doh, for some reason I dismissed that as too simple.
> >>
> >> Regan
> >