[OSM-dev] Ruby help - streams of bits

[SteveC]

can't you do something like

a = ''

a[0] = 123

to set byte 0 of a string to char 123?

On 17 May 2007, at 11:57, Richard Fairhurst wrote:

> Hi all,
>
> I'm working on removing the Ming dependency from Potlatch's GPS code.
> In other words, you won't need Ming to run Potlatch on your own
> machine - you'll only need it to compile the SWF if you want to make
> any changes to Potlatch.
>
> I've rewritten the getgps script to assemble the SWF 'manually', and
> it works exactly as it should. Only trouble is that it's a bit slow.
>
> SWF's opcodes and arguments are encoded as variable-length streams of
> bits. These are all packed in direct succession - i.e. not padded to
> byte boundaries or anything like that.
>
> So, for example, you might have
>
>    00111         5-bit record
>    0110101       7-bit record
>    0000110       7-bit record
>    0001100       7-bit record
>    1111101       7-bit record
>
> which would be packed as
>
>    0b00111011,0b01010000,0b11000011,0b00111110,0b10000000
>                                                (final byte null- 
> padded)
>
> At present I'm doing this by assembling a big big big binary string,
> then splitting it into eight-character strings and converting each one
> into a number. But this is dreadfully slow.
>
> Do any of the Ruby experts here have any better ideas?
>
> cheers
> Richard
>
>
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have fun,

SteveC | steve at asklater.com | http://www.asklater.com/steve/