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diff --git a/contrib/convert-objects/convert-objects.c b/contrib/convert-objects/convert-objects.c
--- /dev/null
@@ -0,0 +1,329 @@
+#include "cache.h"
+#include "blob.h"
+#include "commit.h"
+#include "tree.h"
+
+struct entry {
+ unsigned char old_sha1[20];
+ unsigned char new_sha1[20];
+ int converted;
+};
+
+#define MAXOBJECTS (1000000)
+
+static struct entry *convert[MAXOBJECTS];
+static int nr_convert;
+
+static struct entry * convert_entry(unsigned char *sha1);
+
+static struct entry *insert_new(unsigned char *sha1, int pos)
+{
+ struct entry *new = xcalloc(1, sizeof(struct entry));
+ hashcpy(new->old_sha1, sha1);
+ memmove(convert + pos + 1, convert + pos, (nr_convert - pos) * sizeof(struct entry *));
+ convert[pos] = new;
+ nr_convert++;
+ if (nr_convert == MAXOBJECTS)
+ die("you're kidding me - hit maximum object limit");
+ return new;
+}
+
+static struct entry *lookup_entry(unsigned char *sha1)
+{
+ int low = 0, high = nr_convert;
+
+ while (low < high) {
+ int next = (low + high) / 2;
+ struct entry *n = convert[next];
+ int cmp = hashcmp(sha1, n->old_sha1);
+ if (!cmp)
+ return n;
+ if (cmp < 0) {
+ high = next;
+ continue;
+ }
+ low = next+1;
+ }
+ return insert_new(sha1, low);
+}
+
+static void convert_binary_sha1(void *buffer)
+{
+ struct entry *entry = convert_entry(buffer);
+ hashcpy(buffer, entry->new_sha1);
+}
+
+static void convert_ascii_sha1(void *buffer)
+{
+ unsigned char sha1[20];
+ struct entry *entry;
+
+ if (get_sha1_hex(buffer, sha1))
+ die("expected sha1, got '%s'", (char*) buffer);
+ entry = convert_entry(sha1);
+ memcpy(buffer, sha1_to_hex(entry->new_sha1), 40);
+}
+
+static unsigned int convert_mode(unsigned int mode)
+{
+ unsigned int newmode;
+
+ newmode = mode & S_IFMT;
+ if (S_ISREG(mode))
+ newmode |= (mode & 0100) ? 0755 : 0644;
+ return newmode;
+}
+
+static int write_subdirectory(void *buffer, unsigned long size, const char *base, int baselen, unsigned char *result_sha1)
+{
+ char *new = xmalloc(size);
+ unsigned long newlen = 0;
+ unsigned long used;
+
+ used = 0;
+ while (size) {
+ int len = 21 + strlen(buffer);
+ char *path = strchr(buffer, ' ');
+ unsigned char *sha1;
+ unsigned int mode;
+ char *slash, *origpath;
+
+ if (!path || strtoul_ui(buffer, 8, &mode))
+ die("bad tree conversion");
+ mode = convert_mode(mode);
+ path++;
+ if (memcmp(path, base, baselen))
+ break;
+ origpath = path;
+ path += baselen;
+ slash = strchr(path, '/');
+ if (!slash) {
+ newlen += sprintf(new + newlen, "%o %s", mode, path);
+ new[newlen++] = '\0';
+ hashcpy((unsigned char*)new + newlen, (unsigned char *) buffer + len - 20);
+ newlen += 20;
+
+ used += len;
+ size -= len;
+ buffer = (char *) buffer + len;
+ continue;
+ }
+
+ newlen += sprintf(new + newlen, "%o %.*s", S_IFDIR, (int)(slash - path), path);
+ new[newlen++] = 0;
+ sha1 = (unsigned char *)(new + newlen);
+ newlen += 20;
+
+ len = write_subdirectory(buffer, size, origpath, slash-origpath+1, sha1);
+
+ used += len;
+ size -= len;
+ buffer = (char *) buffer + len;
+ }
+
+ write_sha1_file(new, newlen, tree_type, result_sha1);
+ free(new);
+ return used;
+}
+
+static void convert_tree(void *buffer, unsigned long size, unsigned char *result_sha1)
+{
+ void *orig_buffer = buffer;
+ unsigned long orig_size = size;
+
+ while (size) {
+ size_t len = 1+strlen(buffer);
+
+ convert_binary_sha1((char *) buffer + len);
+
+ len += 20;
+ if (len > size)
+ die("corrupt tree object");
+ size -= len;
+ buffer = (char *) buffer + len;
+ }
+
+ write_subdirectory(orig_buffer, orig_size, "", 0, result_sha1);
+}
+
+static unsigned long parse_oldstyle_date(const char *buf)
+{
+ char c, *p;
+ char buffer[100];
+ struct tm tm;
+ const char *formats[] = {
+ "%c",
+ "%a %b %d %T",
+ "%Z",
+ "%Y",
+ " %Y",
+ NULL
+ };
+ /* We only ever did two timezones in the bad old format .. */
+ const char *timezones[] = {
+ "PDT", "PST", "CEST", NULL
+ };
+ const char **fmt = formats;
+
+ p = buffer;
+ while (isspace(c = *buf))
+ buf++;
+ while ((c = *buf++) != '\n')
+ *p++ = c;
+ *p++ = 0;
+ buf = buffer;
+ memset(&tm, 0, sizeof(tm));
+ do {
+ const char *next = strptime(buf, *fmt, &tm);
+ if (next) {
+ if (!*next)
+ return mktime(&tm);
+ buf = next;
+ } else {
+ const char **p = timezones;
+ while (isspace(*buf))
+ buf++;
+ while (*p) {
+ if (!memcmp(buf, *p, strlen(*p))) {
+ buf += strlen(*p);
+ break;
+ }
+ p++;
+ }
+ }
+ fmt++;
+ } while (*buf && *fmt);
+ printf("left: %s\n", buf);
+ return mktime(&tm);
+}
+
+static int convert_date_line(char *dst, void **buf, unsigned long *sp)
+{
+ unsigned long size = *sp;
+ char *line = *buf;
+ char *next = strchr(line, '\n');
+ char *date = strchr(line, '>');
+ int len;
+
+ if (!next || !date)
+ die("missing or bad author/committer line %s", line);
+ next++; date += 2;
+
+ *buf = next;
+ *sp = size - (next - line);
+
+ len = date - line;
+ memcpy(dst, line, len);
+ dst += len;
+
+ /* Is it already in new format? */
+ if (isdigit(*date)) {
+ int datelen = next - date;
+ memcpy(dst, date, datelen);
+ return len + datelen;
+ }
+
+ /*
+ * Hacky hacky: one of the sparse old-style commits does not have
+ * any date at all, but we can fake it by using the committer date.
+ */
+ if (*date == '\n' && strchr(next, '>'))
+ date = strchr(next, '>')+2;
+
+ return len + sprintf(dst, "%lu -0700\n", parse_oldstyle_date(date));
+}
+
+static void convert_date(void *buffer, unsigned long size, unsigned char *result_sha1)
+{
+ char *new = xmalloc(size + 100);
+ unsigned long newlen = 0;
+
+ /* "tree <sha1>\n" */
+ memcpy(new + newlen, buffer, 46);
+ newlen += 46;
+ buffer = (char *) buffer + 46;
+ size -= 46;
+
+ /* "parent <sha1>\n" */
+ while (!memcmp(buffer, "parent ", 7)) {
+ memcpy(new + newlen, buffer, 48);
+ newlen += 48;
+ buffer = (char *) buffer + 48;
+ size -= 48;
+ }
+
+ /* "author xyz <xyz> date" */
+ newlen += convert_date_line(new + newlen, &buffer, &size);
+ /* "committer xyz <xyz> date" */
+ newlen += convert_date_line(new + newlen, &buffer, &size);
+
+ /* Rest */
+ memcpy(new + newlen, buffer, size);
+ newlen += size;
+
+ write_sha1_file(new, newlen, commit_type, result_sha1);
+ free(new);
+}
+
+static void convert_commit(void *buffer, unsigned long size, unsigned char *result_sha1)
+{
+ void *orig_buffer = buffer;
+ unsigned long orig_size = size;
+
+ if (memcmp(buffer, "tree ", 5))
+ die("Bad commit '%s'", (char*) buffer);
+ convert_ascii_sha1((char *) buffer + 5);
+ buffer = (char *) buffer + 46; /* "tree " + "hex sha1" + "\n" */
+ while (!memcmp(buffer, "parent ", 7)) {
+ convert_ascii_sha1((char *) buffer + 7);
+ buffer = (char *) buffer + 48;
+ }
+ convert_date(orig_buffer, orig_size, result_sha1);
+}
+
+static struct entry * convert_entry(unsigned char *sha1)
+{
+ struct entry *entry = lookup_entry(sha1);
+ enum object_type type;
+ void *buffer, *data;
+ unsigned long size;
+
+ if (entry->converted)
+ return entry;
+ data = read_sha1_file(sha1, &type, &size);
+ if (!data)
+ die("unable to read object %s", sha1_to_hex(sha1));
+
+ buffer = xmalloc(size);
+ memcpy(buffer, data, size);
+
+ if (type == OBJ_BLOB) {
+ write_sha1_file(buffer, size, blob_type, entry->new_sha1);
+ } else if (type == OBJ_TREE)
+ convert_tree(buffer, size, entry->new_sha1);
+ else if (type == OBJ_COMMIT)
+ convert_commit(buffer, size, entry->new_sha1);
+ else
+ die("unknown object type %d in %s", type, sha1_to_hex(sha1));
+ entry->converted = 1;
+ free(buffer);
+ free(data);
+ return entry;
+}
+
+int main(int argc, char **argv)
+{
+ unsigned char sha1[20];
+ struct entry *entry;
+
+ setup_git_directory();
+
+ if (argc != 2)
+ usage("git-convert-objects <sha1>");
+ if (get_sha1(argv[1], sha1))
+ die("Not a valid object name %s", argv[1]);
+
+ entry = convert_entry(sha1);
+ printf("new sha1: %s\n", sha1_to_hex(entry->new_sha1));
+ return 0;
+}