This is the other one for pack_idx.  While here, already start to use
the algo filed to avoid some hardcoded values.

diff /home/op/w/got
commit - 0f043da298c940db3fe16055dcebe4aba60d2834
path + /home/op/w/got
blob - 1b9a3c7d50834fc34fcac7ff7919ea96d024bf44
file + lib/got_lib_pack.h
--- lib/got_lib_pack.h
+++ lib/got_lib_pack.h
@@ -122,6 +122,7 @@ struct got_pack_large_offset_index {
 struct got_packidx {
 	char *path_packidx; /* actual on-disk path */
 	int fd;
+	enum got_hash_algorithm algo;
 	uint8_t *map;
 	size_t len;
 	size_t nlargeobj;
@@ -160,7 +161,7 @@ struct got_packfile_obj_hdr {
 
 const struct got_error *got_packidx_init_hdr(struct got_packidx *, int, off_t);
 const struct got_error *got_packidx_open(struct got_packidx **,
-    int, const char *, int);
+    int, const char *, int, enum got_hash_algorithm);
 const struct got_error *got_packidx_close(struct got_packidx *);
 const struct got_error *got_packidx_get_packfile_path(char **, const char *);
 off_t got_packidx_get_object_offset(struct got_packidx *, int idx);
blob - a17be0408a103339d10ae1a1e9736deb19fb0b74
file + lib/got_lib_privsep.h
--- lib/got_lib_privsep.h
+++ lib/got_lib_privsep.h
@@ -513,6 +513,7 @@ struct got_imsg_index_pack_progress {
 struct got_imsg_packidx {
 	size_t len;
 	off_t packfile_size;
+	int algo;
 	/* Additionally, a file desciptor is passed via imsg. */
 };
 
blob - 84302f45b8db014cc23483d23a273c03f7fa077c
file + lib/pack.c
--- lib/pack.c
+++ lib/pack.c
@@ -75,7 +75,6 @@ const struct got_error *
 got_packidx_init_hdr(struct got_packidx *p, int verify, off_t packfile_size)
 {
 	const struct got_error *err = NULL;
-	enum got_hash_algorithm algo = GOT_HASH_SHA1;
 	struct got_packidx_v2_hdr *h;
 	struct got_hash ctx;
 	uint8_t hash[GOT_HASH_DIGEST_MAXLEN];
@@ -83,7 +82,7 @@ got_packidx_init_hdr(struct got_packidx *p, int verify
 	ssize_t n;
 	int i;
 
-	got_hash_init(&ctx, algo);
+	got_hash_init(&ctx, p->algo);
 
 	h = &p->hdr;
 	offset = 0;
@@ -183,7 +182,7 @@ got_packidx_init_hdr(struct got_packidx *p, int verify
 	remain -= len_fanout;
 
 	nobj = be32toh(h->fanout_table[0xff]);
-	len_ids = nobj * sizeof(*h->sorted_ids);
+	len_ids = nobj * got_hash_digest_length(p->algo);
 	if (len_ids <= nobj || len_ids > remain) {
 		err = got_error(GOT_ERR_BAD_PACKIDX);
 		goto done;
@@ -327,7 +326,7 @@ checksum:
 	}
 	if (verify) {
 		got_hash_update(&ctx, h->trailer->packfile_sha1,
-		    SHA1_DIGEST_LENGTH);
+		    got_hash_digest_length(p->algo));
 		got_hash_final(&ctx, hash);
 		if (got_hash_cmp(ctx.algo, hash, h->trailer->packidx_sha1) != 0)
 			err = got_error(GOT_ERR_PACKIDX_CSUM);
@@ -338,7 +337,8 @@ done:
 
 const struct got_error *
 got_packidx_open(struct got_packidx **packidx,
-    int dir_fd, const char *relpath, int verify)
+    int dir_fd, const char *relpath, int verify,
+    enum got_hash_algorithm algo)
 {
 	const struct got_error *err = NULL;
 	struct got_packidx *p = NULL;
@@ -371,6 +371,8 @@ got_packidx_open(struct got_packidx **packidx,
 		goto done;
 	}
 
+	p->algo = algo;
+
 	p->fd = openat(dir_fd, relpath, O_RDONLY | O_NOFOLLOW | O_CLOEXEC);
 	if (p->fd == -1) {
 		err = got_error_from_errno2("openat", relpath);
blob - 8aa0ad08ca44ef4b71ccf60df2cf2b962c13da78
file + lib/pack_index.c
--- lib/pack_index.c
+++ lib/pack_index.c
@@ -211,7 +211,7 @@ read_packed_object(struct got_pack *pack, struct got_i
 		}
 		if (err)
 			break;
-		got_hash_init(&ctx, GOT_HASH_SHA1);
+		got_hash_init(&ctx, pack->algo);
 		err = got_object_type_label(&obj_label, obj->type);
 		if (err) {
 			free(data);
@@ -414,7 +414,7 @@ resolve_deltified_object(struct got_pack *pack, struct
 		goto done;
 	}
 	headerlen = strlen(header) + 1;
-	got_hash_init(&ctx, GOT_HASH_SHA1);
+	got_hash_init(&ctx, pack->algo);
 	got_hash_update(&ctx, header, headerlen);
 	if (max_size > GOT_DELTA_RESULT_SIZE_CACHED_MAX) {
 		err = read_file_digest(&ctx, tmpfile, len);
@@ -644,7 +644,7 @@ got_pack_index(struct got_pack *pack, int idxfd, FILE 
 		    "bad packfile with zero objects");
 
 	/* We compute the SHA1 of pack file contents and verify later on. */
-	got_hash_init(&ctx, GOT_HASH_SHA1);
+	got_hash_init(&ctx, pack->algo);
 	got_hash_update(&ctx, &hdr, sizeof(hdr));
 
 	/*
blob - 1edd0153662b01a8fd962579a4b5a7c5af42df69
file + lib/privsep.c
--- lib/privsep.c
+++ lib/privsep.c
@@ -1960,6 +1960,7 @@ got_privsep_init_pack_child(struct imsgbuf *ibuf, stru
 
 	ipackidx.len = packidx->len;
 	ipackidx.packfile_size = pack->filesize;
+	ipackidx.algo = packidx->algo;
 	fd = dup(packidx->fd);
 	if (fd == -1)
 		return got_error_from_errno("dup");
blob - 7323331c86c9085cb6ec9fdad463a7ff32f92518
file + lib/repository.c
--- lib/repository.c
+++ lib/repository.c
@@ -1384,7 +1384,7 @@ got_repo_search_packidx(struct got_packidx **packidx, 
 			continue; /* already searched */
 
 		err = got_packidx_open(packidx, got_repo_get_fd(repo),
-		    path_packidx, 0);
+		    path_packidx, 0, repo->algo);
 		if (err)
 			goto done;
 
@@ -1486,7 +1486,7 @@ got_repo_get_packidx(struct got_packidx **packidx, con
 	/* No luck. Search the filesystem. */
 
 	err = got_packidx_open(packidx, got_repo_get_fd(repo),
-	    path_packidx, 0);
+	    path_packidx, 0, repo->algo);
 	if (err)
 		return err;
 
@@ -1817,7 +1817,7 @@ retry:
 		path_packidx = pe->path;
 
 		err = got_packidx_open(&packidx, got_repo_get_fd(repo),
-		    path_packidx, 0);
+		    path_packidx, 0, repo->algo);
 		if (err)
 			break;
 
@@ -2563,7 +2563,7 @@ got_repo_get_packfile_info(int *npackfiles, int *nobje
 		}
 
 		err = got_packidx_open(&packidx, got_repo_get_fd(repo),
-		    path_packidx, 0);
+		    path_packidx, 0, repo->algo);
 		free(path_packidx);
 		if (err)
 			goto done;
blob - b0168b3397ef9e155f6ca23c6057126006b3f1f6
file + lib/repository_admin.c
--- lib/repository_admin.c
+++ lib/repository_admin.c
@@ -548,7 +548,8 @@ got_repo_list_pack(FILE *packfile, struct got_object_i
 		goto done;
 	}
 
-	err = got_packidx_open(&packidx, got_repo_get_fd(repo), idxpath, 1);
+	err = got_packidx_open(&packidx, got_repo_get_fd(repo), idxpath, 1,
+	    repo->algo);
 	if (err)
 		goto done;
 
blob - aec894fa8b4604174f7faf23446d66e16ac0d570
file + libexec/got-read-pack/got-read-pack.c
--- libexec/got-read-pack/got-read-pack.c
+++ libexec/got-read-pack/got-read-pack.c
@@ -1146,6 +1146,7 @@ receive_packidx(struct got_packidx **packidx, struct i
 	}
 	memcpy(&ipackidx, imsg.data, sizeof(ipackidx));
 
+	p->algo = ipackidx.algo;
 	p->fd = imsg_get_fd(&imsg);
 	p->len = ipackidx.len;
 	if (p->fd == -1) {