Signed-off-by: Jeff King <p...@peff.net>
---
 Makefile                    |   1 +
 t/helper/test-tree-bitmap.c | 167 ++++++++++++++++++++++++++++++++++++
 2 files changed, 168 insertions(+)
 create mode 100644 t/helper/test-tree-bitmap.c

diff --git a/Makefile b/Makefile
index 13e1c52478..f6e823f2d6 100644
--- a/Makefile
+++ b/Makefile
@@ -751,6 +751,7 @@ TEST_PROGRAMS_NEED_X += test-parse-options
 TEST_PROGRAMS_NEED_X += test-pkt-line
 TEST_PROGRAMS_NEED_X += test-svn-fe
 TEST_PROGRAMS_NEED_X += test-tool
+TEST_PROGRAMS_NEED_X += test-tree-bitmap
 
 TEST_PROGRAMS = $(patsubst %,t/helper/%$X,$(TEST_PROGRAMS_NEED_X))
 
diff --git a/t/helper/test-tree-bitmap.c b/t/helper/test-tree-bitmap.c
new file mode 100644
index 0000000000..bc5cf0e514
--- /dev/null
+++ b/t/helper/test-tree-bitmap.c
@@ -0,0 +1,167 @@
+#include "cache.h"
+#include "revision.h"
+#include "diffcore.h"
+#include "argv-array.h"
+#include "ewah/ewok.h"
+
+/* map of pathnames to bit positions */
+struct pathmap_entry {
+       struct hashmap_entry ent;
+       unsigned pos;
+       char path[FLEX_ARRAY];
+};
+
+static int pathmap_entry_hashcmp(const void *unused_cmp_data,
+                                const void *entry,
+                                const void *entry_or_key,
+                                const void *keydata)
+{
+       const struct pathmap_entry *a = entry;
+       const struct pathmap_entry *b = entry_or_key;
+       const char *key = keydata;
+
+       return strcmp(a->path, key ? key : b->path);
+}
+
+static int pathmap_entry_strcmp(const void *va, const void *vb)
+{
+       struct pathmap_entry *a = *(struct pathmap_entry **)va;
+       struct pathmap_entry *b = *(struct pathmap_entry **)vb;
+       return strcmp(a->path, b->path);
+}
+
+struct walk_paths_data {
+       struct hashmap *paths;
+       struct commit *commit;
+};
+
+static void walk_paths(diff_format_fn_t fn, struct hashmap *paths)
+{
+       struct argv_array argv = ARGV_ARRAY_INIT;
+       struct rev_info revs;
+       struct walk_paths_data data;
+       struct commit *commit;
+
+       argv_array_pushl(&argv, "rev-list",
+                        "--all", "-t", "--no-renames",
+                        NULL);
+       init_revisions(&revs, NULL);
+       setup_revisions(argv.argc, argv.argv, &revs, NULL);
+       revs.diffopt.output_format = DIFF_FORMAT_CALLBACK;
+       revs.diffopt.format_callback = fn;
+       revs.diffopt.format_callback_data = &data;
+
+       data.paths = paths;
+
+       prepare_revision_walk(&revs);
+       while ((commit = get_revision(&revs))) {
+               data.commit = commit;
+               diff_tree_combined_merge(commit, 0, &revs);
+       }
+
+       reset_revision_walk();
+       argv_array_clear(&argv);
+}
+
+static void collect_commit_paths(struct diff_queue_struct *q,
+                                struct diff_options *opts,
+                                void *vdata)
+{
+       struct walk_paths_data *data = vdata;
+       int i;
+
+       for (i = 0; i < q->nr; i++) {
+               struct diff_filepair *p = q->queue[i];
+               const char *path = p->one->path;
+               struct pathmap_entry *entry;
+               struct hashmap_entry lookup;
+
+               hashmap_entry_init(&lookup, strhash(path));
+               entry = hashmap_get(data->paths, &lookup, path);
+               if (entry)
+                       continue; /* already present */
+
+               FLEX_ALLOC_STR(entry, path, path);
+               entry->ent = lookup;
+               hashmap_put(data->paths, entry);
+       }
+}
+
+/* assign a bit position to all possible paths */
+static void collect_paths(struct hashmap *paths)
+{
+       struct pathmap_entry **sorted;
+       size_t i, n;
+       struct hashmap_iter iter;
+       struct pathmap_entry *entry;
+
+       /* grab all unique paths */
+       hashmap_init(paths, pathmap_entry_hashcmp, NULL, 0);
+       walk_paths(collect_commit_paths, paths);
+
+       /* and assign them bits in sorted order */
+       n = hashmap_get_size(paths);
+       ALLOC_ARRAY(sorted, n);
+       i = 0;
+       for (entry = hashmap_iter_first(paths, &iter);
+            entry;
+            entry = hashmap_iter_next(&iter)) {
+               assert(i < n);
+               sorted[i++] = entry;
+       }
+       QSORT(sorted, i, pathmap_entry_strcmp);
+       for (i = 0; i < n; i++)
+               sorted[i]->pos = i;
+       free(sorted);
+}
+
+/* generate the bitmap for a single commit */
+static void generate_bitmap(struct diff_queue_struct *q,
+                           struct diff_options *opts,
+                           void *vdata)
+{
+       struct walk_paths_data *data = vdata;
+       struct bitmap *bitmap = bitmap_new();
+       struct ewah_bitmap *ewah;
+       struct strbuf out = STRBUF_INIT;
+       size_t i;
+
+       for (i = 0; i < q->nr; i++) {
+               struct diff_filepair *p = q->queue[i];
+               const char *path = p->one->path;
+               struct pathmap_entry *entry;
+               struct hashmap_entry lookup;
+
+               hashmap_entry_init(&lookup, strhash(path));
+               entry = hashmap_get(data->paths, &lookup, path);
+               if (!entry)
+                       BUG("mysterious path appeared: %s", path);
+
+               bitmap_set(bitmap, entry->pos);
+       }
+
+       ewah = bitmap_to_ewah(bitmap);
+       ewah_serialize_strbuf(ewah, &out);
+       fwrite(out.buf, 1, out.len, stdout);
+
+       trace_printf("bitmap %s %u %u",
+                    oid_to_hex(&data->commit->object.oid),
+                    (unsigned)q->nr,
+                    (unsigned)out.len);
+
+       strbuf_release(&out);
+       ewah_free(ewah);
+       bitmap_free(bitmap);
+}
+
+int cmd_main(int argc, const char **argv)
+{
+       struct hashmap paths;
+
+       setup_git_directory();
+       collect_paths(&paths);
+
+       walk_paths(generate_bitmap, &paths);
+
+       return 0;
+}
-- 
2.19.1.550.g7610f1eecb

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