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

[Yuya Nishihara]

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 ?

Other than that, the series looks good to me.