[Freeswitch-dev] Codes I don't understand

[Anthony Minessale]

1) no the += or = makes no difference to me.

2) the macro is designed to fight clipping:
    When a sample exceeds the max size of the datatype we set it to the max
value then cut the volume in half of that sample so it does not make too
much noise.  if we divide everything by 2 then all the volume would be
reduced even on samples that fell inside the proper range.

3) rlen and wlen are often both > 0. the point is we only manupulate the
data that is real rlen is how many bytes on the read channel and wlen the
write, we normalize it so if one of the other is a difference size we only
change samples that are in the range where actual audio occured.




On Mon, Apr 6, 2009 at 10:44 AM, seven du <seven at idapted.com> wrote:

> Well, Thank you Anthony. 3 questions In summary,
>
> 1) in
>
>                        if (x < rlen) {
>                                z += (int32_t) *(fp + x);
>
>
> Any difference if change the "+=" to "=" since z is 0? It just confused me.
>
> 2)  If n1 = 32768, n2 = 32766,  after use MACRO
> switch_normalize_to_16bit(n1)
> switch_normalize_to_16bit(n2)
>
> the result will be:
> n1 = 32767/2 = 16383
> n2 = 32766
>
> is that the expected result?
>
> 3) Is there any chance rlen and wlen both > 0?
>
> On Apr 6, 2009, at 11:16 PM, Anthony Minessale wrote:
>
> what ?
>
> I don't know what your question is.
>
>
>
> On Mon, Apr 6, 2009 at 9:35 AM, seven du <seven at idapted.com> wrote:
>
>> Hi, can someone explain this  to me?
>>
>> In switch_core_media_bug.c, around line 173:
>>
>>
>>
>>                for (x = 0; x < blen; x++) {
>>                        int32_t z = 0;
>>
>>                        if (x < rlen) {
>>                                z += (int32_t) *(fp + x);     //what's
>> difference here with z =
>> (int32_t) *(fp + x) ?
>
>
>>                        }
>>                        if (x < wlen) {
>>                                z += (int32_t) *(dp + x);
>>                        }
>>                        switch_normalize_to_16bit(z);
>>                        *(fp + x) = (int16_t) z / 2;
>>                }
>>
>> And for switch_normalize_to_16bit, according to switch_utils.h,
>>
>> #define SWITCH_SMAX 32767
>> #define SWITCH_SMIN -32768
>> #define switch_normalize_to_16bit(n) if (n > SWITCH_SMAX) n =
>> SWITCH_SMAX / 2; else if (n < SWITCH_SMIN) n = SWITCH_SMIN / 2;
>>
>> Then
>> switch_normalize_to_16bit( 32768 ), z = 32767/2, and (int16_t) z / 2 =
>> 32767/4
>> switch_normalize_to_16bit( 32766) , z = 32766, and (int16_t) z / 2 =
>> 32766/2
>>
>> Does that make sense? I guess it should be like this:
>>
>> #define switch_normalize_to_16bit(n) if (n > SWITCH_SMAX) n =
>> SWITCH_SMAX / 2; else if (n < SWITCH_SMIN) n = SWITCH_SMIN / 2; else n
>> = n / 2;
>>
>>                        switch_normalize_to_16bit(z);
>>                        *(fp + x) = (int16_t) z;
>>
>>
>> Thank you.
>>
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>
>
>
> --
> Anthony Minessale II
>
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-- 
Anthony Minessale II

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