Re: [PATCH] t4062: stop using repetition in regex

["René Scharfe" <l.s.r@web.de>]

Am 09.08.2017 um 19:47 schrieb Junio C Hamano:
> René Scharfe <l.s.r@web.de> writes:
> 
>> There could be any characters except NUL and LF between the 4096 zeros
>> and "0$" for the latter to match wrongly, no?  So there are 4095
>> opportunities for the misleading pattern in a page, with probabilities
>> like this:
>>
>>    0$                          1/256 * 2/256
>>    .0$         254/256       * 1/256 * 2/256
>>    ..0$       (254/256)^2    * 1/256 * 2/256
>>    .{3}0$     (254/256)^3    * 1/256 * 2/256
>>
>>    .{4094}0$  (254/256)^4094 * 1/256 * 2/256
>>
>> That sums up to ca. 1/256 (did that numerically).  Does that make
>> sense?
> 
> Yes, thanks.  I think the number would be different for "^0*$" (the
> above is for "0$") and moves it down to ~1/30000, but as I said,
> allowing additional false success rate is unnecessary (even if it is
> miniscule enough to be acceptable), so let's take the 64*64 patch.

Ah, right, now I get your calculation in the email I replied to above.
"^0*$" has a probability of 2/255 to produce false positives.

Thanks,
René