Re: [Help-smalltalk] Some fixes/improvements to libgst

[Holger Freyther]

> On 14 Jan 2017, at 12:27, Lee Duhem <address@hidden> wrote:
> 

Hi!

another flight, another time to look at it. :)


>>   if (free < (to - from))
>>     {
>> -      memcpy (_gst_cur_bytecodes->ptr, from, free);
>> -      _gst_cur_bytecodes->ptr += free;
>> -      from += free;
>>       realloc_bytecodes (_gst_cur_bytecodes,
>>                         BYTECODE_CHUNK_SIZE + (to - from));
>>     }


> The original logic is that if available space in _gst_cur_bytecodes is
> less than (to - from),
> it will copy part of contents from `from' to _gst_cur_bytecodes, then
> allocate more space
> through realloc_bytecodes(), and copy the rest from `from'.  However,
> the reallocation of
> _gst_cur_bytecodes may need to copy the content of it to the new location.
> 
> And the new code will resize the capacity of _gst_cur_bytecodes first,
> then copy all the contents
> from `from' to it.  In this case, we may save one memcpy call, and
> some extra copying in
> realloc_bytecodes().


Let's do the math now and compare it. My focus is on the from += free
and my suspicion is that we now allocate more memory than before.


free == 10
from == 0
to   == 20
to-fr== 20

Before:
free < to-from          => true
memcpy of 10 bytes
from + free             = 10
realloc CHUNK + 10      =

After:
free < to-from          => true
realloc CHUNK + 20


So I agree that the same data is written, ptr will be correct too but
maybe a tiny bit more memory? What do you think?

holger