Re: [PATCH] cleanup: fix possible overflow errors in binary search, part 2

[Derrick Stolee <stolee@gmail.com>]

On 6/13/2019 1:51 PM, René Scharfe wrote:
> Calculating the sum of two array indexes to find the midpoint between
> them can overflow, i.e. code like this is unsafe for big arrays:
> 
> 	mid = (first + last) >> 1;
> 
> Make sure the intermediate value stays within the boundaries instead,
> like this:
> 
> 	mid = first + ((last - first) >> 1);
> 
> The loop condition of the binary search makes sure that 'last' is
> always greater than 'first', so this is safe as long as 'first' is
> not negative.  And that can be verified easily using the pre-context
> of each change, except for name-hash.c, so add an assertion to that
> effect there.
> 
> The unsafe calculations were found with:
> 
> 	git grep '(.*+.*) *>> *1'
> 
> This is a continuation of 19716b21a4 (cleanup: fix possible overflow
> errors in binary search, 2017-10-08).

Thank you for finding these additional examples!

LGTM. Pretty easy to see this is correct.

-Stolee