Speex dev - Mar 2012 - using unsigned short instead of short for input frame

Thanks for your appreciated help.
i found casting fromunsigned short to short gives different value: unsigned
short FFFF=65535 where short FFFF= -1.
however, can i configure speex codec (specifically speex_encode_int function) to
take input of type unsigned short instead of short so that i avoid casting
errors ?

Regards,
Mashal



________________________________
 From: Yanick Bourbeau <ybourbeau at mrgtech.ca>
To: Mashal al-shboul <shboul8989 at yahoo.com> 
Sent: Friday, March 9, 2012 4:29 PM
Subject: Re: [Speex-dev] using unsigned short instead of short for input frame
 

uint16_t is usually a typedef of an unsigned short or int depending of the
platform. It is supposed to work. About unsigned short to short conversion it is
normal since unsigned short starts at 0 and short starts at -((2^16)/2)-1
[-32767]. If you really want to keep the same numeric value you could cast the
short to unsigned int (32bytes) and add 32767 to the value.

On 12-03-09 02:59 AM, Mashal al-shboul wrote: 
Hi Speex Experts,Thanks for this great mailing list.
>
>
>???? i want to compress a frame of(uint16_t) audio samples, i found that
speex codec assumes input frame of type short. fortunately,both data types are
of? 2-bytes , so my questions :
>- can i cast data types for input to speex?, if so,can i cast uint16_t to
unsigned short and still be accepted by speex ? ,
>because i found converting from uint16_t to short does completely change the
values of the samples(unsigned to signed !).
>
>
>Any help or suggestion is appreciated. Thanks in advance.
>
>
>Regards,
>Mash'al
>
>
>
>
>_______________________________________________
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Hello!

I would like to ask if somebody has managed to use/build Speex in VC2010 
and if yes, how we managed to do that.

Thank you very much.

Hermann

On Mar 9, 2012, at 8:36 AM, Mashal al-shboul wrote:
> i found casting from unsigned short to short gives different value:
unsigned short FFFF=65535 where short FFFF= -1.
Right.

> however, can i configure speex codec (specifically speex_encode_int
function) to take input of type unsigned short instead of short so that i avoid
casting errors ?
I don't know about that, but it should be easy to convert your samples. You
want to convert from the range [0, 2^16 - 1] to [-2^15, 2^15 - 1]. Thus, all you
have to do is subtract 2^15 = 0x8000 from each of them:

steve$ cat a.c
#include <stdio.h>
#include <inttypes.h>

#define convert(x) (int16_t)((x) - 0x8000)

int main()
{
        uint16_t max = 0xffff;
        uint16_t mid = 0x8000;
        uint16_t min = 0x0000;

        printf("%hx -> %hd\n", max, convert(max));
        printf("%hx -> %hd\n", mid, convert(mid));
        printf("%hx -> %hd\n", min, convert(min));
        return 0;
}
steve$ gcc -Wall a.c
steve$ ./a.out
ffff -> 32767
8000 -> 0
0 -> -32768

As you can see, the maximum value 0xffff is indeed converted to 2^15 - 1, the
mid point 0x8000 is converted to 0, and the minimum value 0 is converted to
-2^15.

-- 
Stephen Checkoway