[PATCH v2 01/12] diff-delta: widen `struct delta_index`' size fields to `size_t`

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

Preparation for widening the delta-encoding API to `size_t` in
subsequent commits, which is what lets pack-objects drop the
`cast_size_t_to_ulong()` shims that 606c192380 (odb, packfile: use
size_t for streaming object sizes, 2026-05-08) had to leave behind in
`get_delta()` and `try_delta()` because their downstream consumers were
still narrow.

The struct is private to diff-delta.c, so widening its fields in
isolation is a no-op at runtime: the values stored continue to fit in 32
bits on Windows because the public API around it still truncates.
Splitting it out keeps the API-change commit focused on caller updates.

Since the `memsize` attribute is returned by the `sizeof_delta_index()`
function verbatim, that function's return type is adjusted, too.

Assisted-by: Opus 4.7
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 delta.h      | 2 +-
 diff-delta.c | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/delta.h b/delta.h
index eb5c6d2fdb..ab0279168c 100644
--- a/delta.h
+++ b/delta.h
@@ -28,7 +28,7 @@ void free_delta_index(struct delta_index *index);
  *
  * Given pointer must be what create_delta_index() returned, or NULL.
  */
-unsigned long sizeof_delta_index(struct delta_index *index);
+size_t sizeof_delta_index(struct delta_index *index);
 
 /*
  * create_delta: create a delta from given index for the given buffer
diff --git a/diff-delta.c b/diff-delta.c
index 43c339f010..9e1f9e6f95 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -125,9 +125,9 @@ struct unpacked_index_entry {
 };
 
 struct delta_index {
-	unsigned long memsize;
+	size_t memsize;
 	const void *src_buf;
-	unsigned long src_size;
+	size_t src_size;
 	unsigned int hash_mask;
 	struct index_entry *hash[FLEX_ARRAY];
 };
@@ -140,7 +140,7 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
 	struct unpacked_index_entry *entry, **hash;
 	struct index_entry *packed_entry, **packed_hash;
 	void *mem;
-	unsigned long memsize;
+	size_t memsize;
 
 	if (!buf || !bufsize)
 		return NULL;
@@ -302,7 +302,7 @@ void free_delta_index(struct delta_index *index)
 	free(index);
 }
 
-unsigned long sizeof_delta_index(struct delta_index *index)
+size_t sizeof_delta_index(struct delta_index *index)
 {
 	if (index)
 		return index->memsize;
-- 
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