how not use memmove when insert a object in the list

[John Machin]

On 30/04/2006 11:57 AM, kyo guan wrote:
> Hi :
> 
> 	python list object like a stl vector, if insert a object in the front or the middle of it,
> all the object after the insert point need to move backward.
> 
> look at this code ( in python 2.4.3)
> 

> 	for (i = n; --i >= where; )			/// here, why not use memmove? it would be more speed then this loop.
> 		items[i+1] = items[i];

Here's a guess, based on similar work on another language a few 
reincarnations ago :-)

memmove() is very general-purpose, and starts with byte addresses and a 
byte count. For a small number of list elements, by the time that 
memmove has determined (1) the move overlaps (2) both source and target 
are on word boundaries and it is moving a whole number of words (3) what 
direction (up or down), the DIY code has already finished. For a large 
number of items, memmove *may* be faster (depending on the architecture 
and the compiler) but you are using the wrong data structure anyway.