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From: John Machin on 2 Jun 2010 07:25
On Jun 2, 4:43 pm, johnty <johntyw...(a)gmail.com> wrote:
> i'm reading bytes from a serial port, and storing it into an array.
>
> each byte represents a signed 8-bit int.
>
> currently, the code i'm looking at converts them to an unsigned int by
> doing ord(array[i]). however, what i'd like is to get the _signed_
> integer value. whats the easiest way to do this?

signed = unsigned if unsigned <= 127 else unsigned - 256
From: Patrick Maupin on 4 Jun 2010 15:48
On Jun 2, 6:25 am, John Machin <sjmac...(a)lexicon.net> wrote:
> On Jun 2, 4:43 pm, johnty <johntyw...(a)gmail.com> wrote:
>
> > i'm reading bytes from a serial port, and storing it into an array.
>
> > each byte represents a signed 8-bit int.
>
> > currently, the code i'm looking at converts them to an unsigned int by
> > doing ord(array[i]). however, what i'd like is to get the _signed_
> > integer value. whats the easiest way to do this?
>
> signed = unsigned if unsigned <= 127 else unsigned - 256

That works, but I prefer not using if/else for things that can be
described in an expression without it. Other ways of expressing this
include:

signed = (unsigned & 127) - (unsigned & 128)
signed = (unsigned & 127) * 2 - unsigned
signed - unsigned - 2 * (unsigned & 128)

Regards,
Pat
From: John Nagle on 4 Jun 2010 16:26
johnty wrote:
> i'm reading bytes from a serial port, and storing it into an array.

Try reading into a type "bytearray". That's the proper data type
for raw bytes.

John Nagle
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