std.file.read implementation contest

[Steven Schveighoffer]

"Andrei Alexandrescu" wrote
> Steven Schveighoffer wrote:
>> "Andrei Alexandrescu" wrote
>>> Someone mentioned an old bug in std.file.read here:
>>>
>>> http://www.reddit.com/r/programming/comments/7xnty/walter_bright_on_porting_d_to_the_mac/
>>>
>>> Two programmers sent in patches for the function. Which is to be 
>>> committed and why? (Linux versions shown. Apologies for noisy line 
>>> breaks.)
>>
>> Implementation 2, save 1 bug:
> [snip]
>
> Aha, cool. Thanks for the info. I've adapted the code to still only use 
> one loop:
>
> void[] read(string name)
> {
>     immutable fd = std.c.linux.linux.open(toStringz(name), O_RDONLY);
>     cenforce(fd != -1, name);
>     scope(exit) std.c.linux.linux.close(fd);
>
>     struct_stat statbuf = void;
>     cenforce(std.c.linux.linux.fstat(fd, &statbuf) == 0, name);
>
>     immutable initialAlloc = statbuf.st_size
>         ? (statbuf.st_size + 16) & 15
>         : 1024;

Hm... won't this allocate only 15 bytes max if st_size is nonzero?

I think you meant:
(statbuf.st_size + 16) & ~15

Two more points:

if you allocate a size of 16, I think you'll actually get 32 bytes because 
of the sentinel byte.  Somehow you should account for that, or you 
automatically double the allocation size each time (or at least a page more 
than you want).

And the increments are not in 16, they are in powers of 2 *starting* with 
16.  For example, if you allocate a size of 80 bytes (16 * 5), you will 
actually get 128 bytes.

Other than that, it looks good.

-Steve