[mkgmap-dev] methods to write signed / unsigned integers

Tue Feb 20 09:15:11 GMT 2018

Hi Ticker,

please explain why you think that this is important. I like the idea that I don't have to care about the
write method, I only have to make sure that the fields can hold the value ranges. In most cases we can
use int even if IMG format uses a single byte, since we don't have huge amounts of header structures.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Montag, 19. Februar 2018 10:19:56
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] methods to write signed / unsigned integers

Hi

I think it is important to indicate if a signed or unsigned is being
written so that the range can be asserted:

eg:
        public void putU1(int val) {
                assert val >= 0 && val <= 255 : val;
                buf.put((byte)val);
        }
and
        public void putS1(int val) {
                assert val >= -128
&& val <= 127 : val;
                buf.put((byte)val);
        }

Ticker

On Sun, 2018-02-18 at 21:37 +0000, Steve Ratcliffe wrote:
> Hi Gerd, Ticker
>
> For ImgFileWriter I think we should just have put1(int), put2(int),
> put3(int)
> and put4(int) and remove put(byte), putChar(char) and putInt(int).
>
> So each method takes an int, so no casting is needed.  There is no
> difference between writing unisigned and signed for any value
> that fits into an int.
>
> To write unsigned values greater than 2G then technically you
> need a long, so an unsigned version could be added as a
> default method on the interface put4u(long val) rather than
> having to implement across multiple implementations.
>
> Although I don't think it is necessary if you want to add
> signed/unsigned methods that range check the value, then
> again add them as default method on the interface.
>
> I've attached a patch that implements this.
>
> Reading is different, we do need signed/unsigned versions.
> I'd suggest that again have get{1,2,3,4} and remove getChar and
> getInt special cases, and then get1u() etc for unsigned results.
> All of these returning int probably, depending on what results
> in the best looking code.  I have not done a patch for that.
>
> ..Steve
>
> > we have various methods to write an integer with 1, 2, 3, or 4
> > bytes to an img file.
> > I always feel unsure what method to use because none of them makes
> > clear what happens with negative values.
> >
> > Besides that some of the existing routines seem to throw misleading
> > exceptions,
> > e.g. FileBackedImgFileWriter seems to assume that it is only used
> > for the mdr tmp file and creates texts like this:
> > throw new MapFailedException("could not write3 to mdr tmp file");
> > throw new MapFailedException("could not write put3 to mdr tmp
> > file");
> >
> > Only the javadoc for put1() and put2() tell me the range (0..255 or
> > 0..65535) .
> >
> > If I got that right put3() allows negative values, so I think it is
> > NOT 0..16777215 but -8388608 .. 8388607 ?
> >
> > I'd like to improve the readability of the code, but I don't want
> > to mess up anything.
> > Would it be possible to add comments to all the methods?
> >
> > Gerd
> >
> >
> >
> > _______________________________________________
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> > mkgmap-dev at lists.mkgmap.org.uk
> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> >
>
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