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

[Boris Feld]

# 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;
+}
+
 static inline int nt_level(const char *node, Py_ssize_t level)
 {
 	int v = node[level >> 1];