Re: [PATCH -ac] Panicking in morse code

[Richard B. Johnson]

On Fri, 26 Jul 2002, Bill Davidsen wrote:

> On Fri, 26 Jul 2002, Daniel Phillips wrote:
> 
> > On Thursday 25 July 2002 14:51, Bill Davidsen wrote:
> > > On Fri, 19 Jul 2002, Alan Cox wrote:
> > > 
> > > > > +static const char * morse[] = {
> > > > > +	".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", /* A-H */
> [...snip...]
> > > > 
> > > > How about using bitmasks here. Say top five bits being the length, lower
> > > > 5 bits being 1 for dash 0 for dit ?
> > > 
> > > ??? If the length is 1..5 I suspect you could use the top two bits and fit
> > > the whole thing in a byte. But since bytes work well, use the top three
> > > bits for length without the one bit offset. Still a big win over strings,
> > > although a LOT harder to get right by eye.
> > 
> > Please read back through the thread and see how 255 different 7 bit codes
> > complete with lengths can be packed into 8 bits.
> 
> ???
>  1 - there are not 255 different 7 bit values, there are 128
>  2 - morse code has a longest value of 5 elements not 7

The '.' (also called full-stop) is 6 elements long. The ',' is also
6 elements long. For a correct implimentation, i.e., one that sounds
correct, you need to encode a 'pause' element into each symbol. This
is because the pause between Morse characters is sometimes ahead
of a character and sometimes behind a character (the pause is ahead
of characters starting with a dot and after characters ending with a
dot, including characters of all dots -- except for numbers, which
have pauses after them). In a previously life, I had to develop
the correct "fist" to pass the Socond Class Radio Telegraph License.

This means that it is probably best to use one 8-byte character
for each Morse-code character.

If anybody's interested I have some DOS assembly circa 1987 that
did this stuff. It ignored the correct "fist", and has spaces after
each character. It doesn't sound too bad.

>  3 - Alan was talking about len+val representation, not stop-bit patterns,
>      which is what I guess you mean

Cheers,
Dick Johnson
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