[PATCH 3 of 7 V4] sparse-revlog: add a `index_segment_span` function in C

[Boris FELD]

On 21/11/2018 13:27, Yuya Nishihara wrote:
> On Tue, 20 Nov 2018 21:44:34 +0100, Boris Feld wrote:
>> # HG changeset patch
>> # User Boris Feld <boris.feld at octobus.net>
>> # Date 1541785396 -3600
>> #      Fri Nov 09 18:43:16 2018 +0100
>> # Node ID 5bb00d137c14d311c91c7a4f32f58378cd9195ec
>> # Parent  8863dc1f7d078827708d178bbbfee5519b4c9b0f
>> # EXP-Topic sparse-perf
>> # Available At https://bitbucket.org/octobus/mercurial-devel/
>> #              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 5bb00d137c14
>> sparse-revlog: add a `index_segment_span` function in C
>>
>> We are about to implement a native version of `slicechunktodensity`. For
>> clarity, we introduce the helper functions first. This new function provides
>> an efficient way to retrieve some of the information needed by
>> `slicechunktodensity`.
>>
>> diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
>> --- a/mercurial/cext/revlog.c
>> +++ b/mercurial/cext/revlog.c
>> @@ -1068,6 +1068,27 @@ bail:
>>  	return NULL;
>>  }
>>  
>> +static inline int64_t
>> +index_segment_span(indexObject *self, Py_ssize_t start_rev, Py_ssize_t end_rev)
>> +{
>> +	int64_t start_offset;
>> +	int64_t end_offset;
>> +	int end_size;
>> +	start_offset = index_get_start(self, start_rev);
>> +	if (start_offset < 0) {
>> +		return -1;
>> +	}
>> +	end_offset = index_get_start(self, end_rev);
>> +	if (end_offset < 0) {
>> +		return -1;
>> +	}
>> +	end_size = index_get_length(self, end_rev);
>> +	if (end_size < 0) {
>> +		return -1;
>> +	}
>> +	return (end_offset - start_offset) + (int64_t)end_size;
> Nit: maybe raise error if end_offset - start_offset) + (int64_t)end_size < 0 ?

Unless the revlog is corrupted, we have:

  start_rev <= end_rev

and:

  start_offset <= end_offset

So this value will be positive. If the revlog is corrupt I assume we'll
have more troubles sooner.

Or do you want extra checks on the above assertion?
>
> Other than that, the series looks good to me.
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