Re: [PATCH] fast-export: avoid NULL pointer arithmetic

[René Scharfe]

Am 12.05.2018 um 10:45 schrieb René Scharfe:
> Or we could roll our own custom hash map, as I mused in an earlier post.
> That would duplicate quite a bit of code; are there reusable pieces
> hidden within that could be extracted into common functions?

At least it would allow us to save four bytes of padding per object on
x64 by using a separate array for the hash map values; not sure how that
would impact performance, though.

---
 builtin/fast-export.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 627b0032f3..086fcaf9ea 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -72,13 +72,13 @@ static int parse_opt_tag_of_filtered_mode(const struct 
option *opt,
 
 struct object_mark_entry {
        const struct object *base;
-       uint32_t mark;
 };
 
 struct object_marks {
        unsigned int size;
        unsigned int nr;
        struct object_mark_entry *entries;
+       uint32_t *marks;
 };
 
 static struct object_marks idnums;
@@ -98,14 +98,14 @@ static void set_object_mark(struct object_marks *n, const 
struct object *base,
 
        while (entries[j].base) {
                if (entries[j].base == base) {
-                       entries[j].mark = mark;
+                       n->marks[j] = mark;
                        return;
                }
                if (++j >= size)
                        j = 0;
        }
        entries[j].base = base;
-       entries[j].mark = mark;
+       n->marks[j] = mark;
        n->nr++;
 }
 
@@ -114,19 +114,22 @@ static void grow_object_marks(struct object_marks *n)
        unsigned int i;
        unsigned int old_size = n->size;
        struct object_mark_entry *old_entries = n->entries;
+       uint32_t *old_marks = n->marks;
 
        n->size = (old_size + 1000) * 3 / 2;
        n->entries = xcalloc(n->size, sizeof(n->entries[0]));
+       n->marks = xcalloc(n->size, sizeof(n->marks[0]));
        n->nr = 0;
 
        for (i = 0; i < old_size; i++) {
                const struct object *base = old_entries[i].base;
-               uint32_t mark = old_entries[i].mark;
+               uint32_t mark = old_marks[i];
 
                if (mark)
                        set_object_mark(n, base, mark);
        }
        free(old_entries);
+       free(old_marks);
 }
 
 static int has_unshown_parent(struct commit *commit)
@@ -236,7 +239,7 @@ static int get_object_mark(struct object *object)
        for (;;) {
                struct object_mark_entry *ref = idnums.entries + j;
                if (ref->base == object)
-                       return ref->mark;
+                       return idnums.marks[j];
                if (!ref->base)
                        return 0;
                if (++j == idnums.size)
@@ -966,7 +969,7 @@ static void export_marks(char *file)
 
        for (i = 0; i < idnums.size; i++) {
                if (entry->base && entry->base->type == 1) {
-                       if (fprintf(f, ":%"PRIu32" %s\n", entry->mark,
+                       if (fprintf(f, ":%"PRIu32" %s\n", idnums.marks[i],
                                    oid_to_hex(&entry->base->oid)) < 0) {
                            e = 1;
                            break;
-- 
2.17.0