# Diff Range Underflow

2 messages from 2018-10-07 to 2018-10-12. Participants: Era, Johannes Schindelin.
Thread: https://gitlist.dev/t/49503

## Era, 2018-10-07 13:47

Subject: Diff Range Underflow
Message-ID: <ED62D6B5-9227-4FC9-AB77-7DB4D3835501@gmail.com>
URL: https://gitlist.dev/e/ED62D6B5-9227-4FC9-AB77-7DB4D3835501%40gmail.com

```
I discovered an apparent underflow when using the —unified=0 / -U0 flag with git-show on a merge commit.
Leaving the flag on its default value or 1 shows the ranges correctly.

	$git --no-pager show -z --no-color --pretty=%x00%s%x00%b%x00 -U1 3ac9cfed9ce01836dea1fee96c4eceb2df4b6878

produces a diff with the following ranges

	@@@ -582,2 -599,19 +582,1 @@@ extension TranslationContentViewControl

changing the flag to -U0 like so

	git --no-pager show -z --no-color --pretty=%x00%s%x00%b%x00 -U0 3ac9cfed9ce01836dea1fee96c4eceb2df4b6878

results in the following ranges begin output

	@@@ -583,0 -600,17 +583,18446744073709551615 @@@ extension TranslationContentViewControl


Obviously this is some sort of underflow bug.
Unfortunately I cant share the original repo or diff.


Best regards,
Erik







```

## Johannes Schindelin, 2018-10-12 08:10

Subject: Re: Diff Range Underflow
Message-ID: <nycvar.QRO.7.76.6.1810121009060.45@tvgsbejvaqbjf.bet>
URL: https://gitlist.dev/e/nycvar.QRO.7.76.6.1810121009060.45%40tvgsbejvaqbjf.bet
In-Reply-To: <ED62D6B5-9227-4FC9-AB77-7DB4D3835501@gmail.com>

```
Hi Era,

On Sun, 7 Oct 2018, Era wrote:

> I discovered an apparent underflow when using the —unified=0 / -U0 flag with git-show on a merge commit.
> Leaving the flag on its default value or 1 shows the ranges correctly.
> 
> 	$git --no-pager show -z --no-color --pretty=%x00%s%x00%b%x00 -U1 3ac9cfed9ce01836dea1fee96c4eceb2df4b6878
> 
> produces a diff with the following ranges
> 
> 	@@@ -582,2 -599,19 +582,1 @@@ extension TranslationContentViewControl
> 
> changing the flag to -U0 like so
> 
> 	git --no-pager show -z --no-color --pretty=%x00%s%x00%b%x00 -U0 3ac9cfed9ce01836dea1fee96c4eceb2df4b6878
> 
> results in the following ranges begin output
> 
> 	@@@ -583,0 -600,17 +583,18446744073709551615 @@@ extension TranslationContentViewControl
> 
> 
> Obviously this is some sort of underflow bug.
> Unfortunately I cant share the original repo or diff.

Happily, you can work on reproducing this with a public repository, or
even better: with two crafted files that can be compared via `git diff
--no-index ...` to trigger the bug, starting with the blob contents you
cannot share and editing them down to the minimal size, changing the
contents to no longer contain any sensitive information. Please do so.

Ciao,
Johannes

> 
> 
> Best regards,
> Erik
> 
> 
> 
> 
> 
> 
> 
```