Re: [PATCH 2/2] radix-tree: Fix optimisation problem

From: Cedric Blancher
Date: Sun Sep 25 2016 - 13:59:36 EST

On 25 September 2016 at 02:18, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, Sep 24, 2016 at 4:35 PM, Cedric Blancher
> <cedric.blancher@xxxxxxxxx> wrote:
>>> void *entry = parent->slots[offset];
>>> int siboff = entry - parent->slots;
>> If entry is a pointer to void, how can you do pointer arithmetic with it?
> It's actually void **.
> (That said, gcc has an extension that considers "void *" to be a byte
> pointer, so you can actually do arithmetic on them, and it acts like
> "char *")
>> Also, if you use pointer distances, the use of int is not valid, it
>> should then be ptrdiff_t siboff.
> The use of "int" is perfectly valid, since it's limited by
> RADIX_TREE_MAP_SIZE, so it's going to be a small integer.

A specific data type would be wise (aka radtr_mapsz_t) to prevent a
disaster as SystemV had early during development. It took AT&T TWO
fucking months to figure out that their avl tree implementation had a
small type problem with int vs long.
Since I'd expect no one cares I'm going to print this email so I can
send the scan as PDF each time you hit that problem in the future with
"told you so"

Cedric Blancher <cedric.blancher@xxxxxxxxx>
Institute Pasteur