On 10/14/2018 10:29 AM, René Scharfe wrote:
It still has some repetition, converted code is a bit longer than the
current one, and I don't know how to build a Coccinelle rule that would
do that conversion.
Looked for a possibility to at least leave QSORT call-sites alone by
enhancing that macro, but didn't find any. Found a few websites
showing off mindblowing macros, thouhg, this one in particular:
https://github.com/pfultz2/Cloak/wiki/C-Preprocessor-tricks,-tips,-and-idioms
Anyway, drove the generative approach a bit further, and came up with
the new DEFINE_SORT below. I'm unsure about the name; perhaps it should
be called DEFINE_SORT_BY_COMPARE_FUNCTION_BODY, but that's a bit long.
It handles casts and const attributes behind the scenes and avoids
repetition, but looks a bit weird, as it is placed where a function
signature would go.
Apart from that the macro is simple and doesn't use any tricks or
added checks. It just sets up boilerplate functions to offer type-safe
sorting.
diffcore-rename.c and refs/packed-backend.c receive special treatment in
the patch because their compare functions are used outside of sorting as
well. I made them take typed pointers nevertheless and used them from
DEFINE_SORT; the wrapper generated by that macro is supposed to be
private. Given that such reuse is rare and I think we don't need a way
to make it public.
What do y'all think about this direction?
---
[snip]
diff --git a/git-compat-util.h b/git-compat-util.h
index 5f2e90932f..491230fc57 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1066,6 +1066,21 @@ static inline void sane_qsort(void *base, size_t nmemb, size_t size,
qsort(base, nmemb, size, compar);
}
+#define DECLARE_SORT(scope, name, elemtype) \
+scope void name(elemtype, size_t)
+
+#define DEFINE_SORT(scope, name, elemtype, one, two) \
+static int name##_compare(const elemtype, const elemtype); \
+static int name##_compare_void(const void *a, const void *b) \
+{ \
+ return name##_compare(a, b); \
+} \
+scope void name(elemtype base, size_t nmemb) \
+{ \
+ QSORT(base, nmemb, name##_compare_void); \
+} \
+static int name##_compare(const elemtype one, const elemtype two)
+
Since you were worried about the "private" name of the compare function,
maybe split this macro into two: DEFINE_COMPARE and DEFINE_SORT. Then,
if someone wants direct access to the compare function, they could use
the DEFINE_COMPARE to ensure the typing is correct, and use QSORT as
normal with name##_compare_void.
As I think about this, I think this is less of a problem than is worth
this split. The commit-slab definitions generate a lot of methods using
the "name##" convention, so perhaps we should just trust developers
using the macros to look up the macro definition or similar examples. In
that sense, including a conversion that consumes the compare function
directly can be a signpost for future callers.
I would say that maybe the times where you need to do something special
should be pulled out into their own patches, so we can call attention to
them directly.
[snip]
diff --git a/midx.c b/midx.c
index 713d6f9dde..4407db7949 100644
--- a/midx.c
+++ b/midx.c
@@ -419,10 +419,8 @@ struct pack_pair {
char *pack_name;
};
-static int pack_pair_compare(const void *_a, const void *_b)
+DEFINE_SORT(static, sort_by_pack_name, struct pack_pair *, a, b)
{
- struct pack_pair *a = (struct pack_pair *)_a;
- struct pack_pair *b = (struct pack_pair *)_b;
return strcmp(a->pack_name, b->pack_name);
}
@@ -438,7 +436,7 @@ static void sort_packs_by_name(char **pack_names, uint32_t nr_packs, uint32_t *p
pairs[i].pack_name = pack_names[i];
}
- QSORT(pairs, nr_packs, pack_pair_compare);
+ sort_by_pack_name(pairs, nr_packs);
I like this "sort_by_" convention..
for (i = 0; i < nr_packs; i++) {
pack_names[i] = pairs[i].pack_name;
@@ -455,10 +453,8 @@ struct pack_midx_entry {
uint64_t offset;
};
-static int midx_oid_compare(const void *_a, const void *_b)
+DEFINE_SORT(static, sort_midx, struct pack_midx_entry *, a, b)
{
- const struct pack_midx_entry *a = (const struct pack_midx_entry *)_a;
- const struct pack_midx_entry *b = (const struct pack_midx_entry *)_b;
int cmp = oidcmp(&a->oid, &b->oid);
if (cmp)
@@ -573,7 +569,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
}
}
- QSORT(entries_by_fanout, nr_fanout, midx_oid_compare);
+ sort_midx(entries_by_fanout, nr_fanout);
...but it isn't followed here. Perhaps "sort_by_oid"?
Thanks,
-Stolee
