thodg/libgit2

diff --git a/src/blob.c b/src/blob.c
index 60a6b55..20dcece 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -42,7 +42,7 @@ int git_blob__parse(git_blob *blob, git_odb_object *odb_obj)
 	assert(blob);
 	git_cached_obj_incref((git_cached_obj *)odb_obj);
 	blob->odb_object = odb_obj;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int git_blob_create_frombuffer(git_oid *oid, git_repository *repo, const void *buffer, size_t len)
@@ -51,58 +51,50 @@ int git_blob_create_frombuffer(git_oid *oid, git_repository *repo, const void *b
 	git_odb *odb;
 	git_odb_stream *stream;
 
-	error = git_repository_odb__weakptr(&odb, repo);
-	if (error < GIT_SUCCESS)
+	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0 ||
+		(error = git_odb_open_wstream(&stream, odb, len, GIT_OBJ_BLOB)) < 0)
 		return error;
 
-	if ((error = git_odb_open_wstream(&stream, odb, len, GIT_OBJ_BLOB)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to create blob");
+	if ((error = stream->write(stream, buffer, len)) == 0)
+		error = stream->finalize_write(oid, stream);
 
-	if ((error = stream->write(stream, buffer, len)) < GIT_SUCCESS) {
-		stream->free(stream);
-		return error;
-	}
-
-	error = stream->finalize_write(oid, stream);
 	stream->free(stream);
-
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to create blob");
-
-	return GIT_SUCCESS;
+	return error;
 }
 
-static int write_file_stream(git_oid *oid, git_odb *odb, const char *path, git_off_t file_size)
+static int write_file_stream(
+	git_oid *oid, git_odb *odb, const char *path, git_off_t file_size)
 {
 	int fd, error;
 	char buffer[4096];
 	git_odb_stream *stream = NULL;
 
-	if ((error = git_odb_open_wstream(&stream, odb, (size_t)file_size, GIT_OBJ_BLOB)) < GIT_SUCCESS)
+	if ((error = git_odb_open_wstream(
+			&stream, odb, (size_t)file_size, GIT_OBJ_BLOB)) < 0)
 		return error;
 
-	if ((fd = p_open(path, O_RDONLY)) < 0) {
-		error = git__throw(GIT_ENOTFOUND, "Failed to create blob. Could not open '%s'", path);
-		goto cleanup;
+	if ((fd = git_futils_open_ro(path)) < 0) {
+		stream->free(stream);
+		return -1;
 	}
 
-	while (file_size > 0) {
+	while (!error && file_size > 0) {
 		ssize_t read_len = p_read(fd, buffer, sizeof(buffer));
 
 		if (read_len < 0) {
-			error = git__throw(GIT_EOSERR, "Failed to create blob. Can't read full file");
-			p_close(fd);
-			goto cleanup;
+			giterr_set(
+				GITERR_OS, "Failed to create blob. Can't read whole file");
+			error = -1;
 		}
-
-		stream->write(stream, buffer, read_len);
-		file_size -= read_len;
+		else if (!(error = stream->write(stream, buffer, read_len)))
+			file_size -= read_len;
 	}
 
 	p_close(fd);
-	error = stream->finalize_write(oid, stream);
 
-cleanup:
+	if (!error)
+		error = stream->finalize_write(oid, stream);
+
 	stream->free(stream);
 	return error;
 }
@@ -117,8 +109,7 @@ static int write_file_filtered(
 	git_buf source = GIT_BUF_INIT;
 	git_buf dest = GIT_BUF_INIT;
 
-	error = git_futils_readbuffer(&source, full_path);
-	if (error < GIT_SUCCESS)
+	if ((error = git_futils_readbuffer(&source, full_path)) < 0)
 		return error;
 
 	error = git_filters_apply(&dest, &source, filters);
@@ -127,30 +118,29 @@ static int write_file_filtered(
 	 * and we don't want to ODB write to choke */
 	git_buf_free(&source);
 
-	if (error == GIT_SUCCESS) {
-		/* Write the file to disk if it was properly filtered */
+	/* Write the file to disk if it was properly filtered */
+	if (!error)
 		error = git_odb_write(oid, odb, dest.ptr, dest.size, GIT_OBJ_BLOB);
-	}
 
 	git_buf_free(&dest);
-	return GIT_SUCCESS;
+	return error;
 }
 
-static int write_symlink(git_oid *oid, git_odb *odb, const char *path, size_t link_size)
+static int write_symlink(
+	git_oid *oid, git_odb *odb, const char *path, size_t link_size)
 {
 	char *link_data;
 	ssize_t read_len;
 	int error;
 
 	link_data = git__malloc(link_size);
-	if (!link_data)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(link_data);
 
 	read_len = p_readlink(path, link_data, link_size);
-
 	if (read_len != (ssize_t)link_size) {
+		giterr_set(GITERR_OS, "Failed to create blob.  Can't read symlink '%s'", path);
 		free(link_data);
-		return git__throw(GIT_EOSERR, "Failed to create blob. Can't read symlink");
+		return -1;
 	}
 
 	error = git_odb_write(oid, odb, (void *)link_data, link_size, GIT_OBJ_BLOB);
@@ -168,25 +158,18 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 	git_odb *odb = NULL;
 
 	workdir = git_repository_workdir(repo);
-	if (workdir == NULL)
-		return git__throw(GIT_ENOTFOUND, "Failed to create blob. (No working directory found)");
+	assert(workdir); /* error to call this on bare repo */
 
-	error = git_buf_joinpath(&full_path, workdir, path);
-	if (error < GIT_SUCCESS)
+	if ((error = git_buf_joinpath(&full_path, workdir, path)) < 0 ||
+		(error = git_path_lstat(full_path.ptr, &st)) < 0 ||
+		(error = git_repository_odb__weakptr(&odb, repo)) < 0)
+	{
+		git_buf_free(&full_path);
 		return error;
-
-	error = p_lstat(full_path.ptr, &st);
-	if (error < 0) {
-		error = git__throw(GIT_EOSERR, "Failed to stat blob. %s", strerror(errno));
-		goto cleanup;
 	}
 
 	size = st.st_size;
 
-	error = git_repository_odb__weakptr(&odb, repo);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
 	if (S_ISLNK(st.st_mode)) {
 		error = write_symlink(oid, odb, full_path.ptr, (size_t)size);
 	} else {
@@ -194,12 +177,12 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 		int filter_count;
 
 		/* Load the filters for writing this file to the ODB */
-		filter_count = git_filters_load(&write_filters, repo, path, GIT_FILTER_TO_ODB);
+		filter_count = git_filters_load(
+			&write_filters, repo, path, GIT_FILTER_TO_ODB);
 
 		if (filter_count < 0) {
 			/* Negative value means there was a critical error */
 			error = filter_count;
-			goto cleanup;
 		} else if (filter_count == 0) {
 			/* No filters need to be applied to the document: we can stream
 			 * directly from disk */
@@ -212,19 +195,20 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 		git_filters_free(&write_filters);
 
 		/*
-		 * TODO: eventually support streaming filtered files, for files which are bigger
-		 * than a given threshold. This is not a priority because applying a filter in
-		 * streaming mode changes the final size of the blob, and without knowing its
-		 * final size, the blob cannot be written in stream mode to the ODB.
+		 * TODO: eventually support streaming filtered files, for files
+		 * which are bigger than a given threshold. This is not a priority
+		 * because applying a filter in streaming mode changes the final
+		 * size of the blob, and without knowing its final size, the blob
+		 * cannot be written in stream mode to the ODB.
 		 *
-		 * The plan is to do streaming writes to a tempfile on disk and then opening
-		 * streaming that file to the ODB, using `write_file_stream`.
+		 * The plan is to do streaming writes to a tempfile on disk and then
+		 * opening streaming that file to the ODB, using
+		 * `write_file_stream`.
 		 *
 		 * CAREFULLY DESIGNED APIS YO
 		 */
 	}
 
-cleanup:
 	git_buf_free(&full_path);
 	return error;
 }
diff --git a/src/buffer.c b/src/buffer.c
index dd245e2..b0e3299 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -215,8 +215,8 @@ void git_buf_truncate(git_buf *buf, size_t len)
 
 void git_buf_rtruncate_at_char(git_buf *buf, char separator)
 {
-	int idx = git_buf_rfind_next(buf, separator);
-	git_buf_truncate(buf, idx < 0 ? 0 : idx);
+	ssize_t idx = git_buf_rfind_next(buf, separator);
+	git_buf_truncate(buf, idx < 0 ? 0 : (size_t)idx);
 }
 
 void git_buf_swap(git_buf *buf_a, git_buf *buf_b)
diff --git a/src/buffer.h b/src/buffer.h
index 6f59dce..d90db4d 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -102,9 +102,9 @@ void git_buf_copy_cstr(char *data, size_t datasize, const git_buf *buf);
 
 #define git_buf_PUTS(buf, str) git_buf_put(buf, str, sizeof(str) - 1)
 
-GIT_INLINE(int) git_buf_rfind_next(git_buf *buf, char ch)
+GIT_INLINE(ssize_t) git_buf_rfind_next(git_buf *buf, char ch)
 {
-	int idx = buf->size - 1;
+	ssize_t idx = (ssize_t)buf->size - 1;
 	while (idx >= 0 && buf->ptr[idx] == ch) idx--;
 	while (idx >= 0 && buf->ptr[idx] != ch) idx--;
 	return idx;
diff --git a/src/fileops.c b/src/fileops.c
index 0ce4882..aa52b09 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -79,11 +79,25 @@ int git_futils_creat_locked_withpath(const char *path, const mode_t dirmode, con
 	return git_futils_creat_locked(path, mode);
 }
 
+int git_futils_open_ro(const char *path)
+{
+	int fd = p_open(path, O_RDONLY);
+	if (fd < 0) {
+		if (errno == ENOENT)
+			fd = GIT_ENOTFOUND;
+		giterr_set(GITERR_OS, "Failed to open '%s'", path);
+	}
+	return fd;
+}
+
 git_off_t git_futils_filesize(git_file fd)
 {
 	struct stat sb;
-	if (p_fstat(fd, &sb))
-		return GIT_ERROR;
+
+	if (p_fstat(fd, &sb)) {
+		giterr_set(GITERR_OS, "Failed to stat file descriptor");
+		return -1;
+	}
 
 	return sb.st_size;
 }
@@ -176,10 +190,15 @@ int git_futils_readbuffer(git_buf *buf, const char *path)
 
 int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmode)
 {
-	if (git_futils_mkpath2file(to, dirmode) < GIT_SUCCESS)
-		return GIT_EOSERR;	/* The callee already takes care of setting the correct error message. */
+	if (git_futils_mkpath2file(to, dirmode) < 0)
+		return -1;
 
-	return p_rename(from, to); /* The callee already takes care of setting the correct error message. */
+	if (p_rename(from, to) < 0) {
+		giterr_set(GITERR_OS, "Failed to rename '%s' to '%s'", from, to);
+		return -1;
+	}
+
+	return 0;
 }
 
 int git_futils_mmap_ro(git_map *out, git_file fd, git_off_t begin, size_t len)
@@ -192,8 +211,10 @@ int git_futils_mmap_ro_file(git_map *out, const char *path)
 	git_file fd = p_open(path, O_RDONLY /* | O_NOATIME */);
 	git_off_t len = git_futils_filesize(fd);
 	int result;
-	if (!git__is_sizet(len))
-		return git__throw(GIT_ERROR, "File `%s` too large to mmap", path);
+	if (!git__is_sizet(len)) {
+		giterr_set(GITERR_OS, "File `%s` too large to mmap", path);
+		return -1;
+	}
 	result = git_futils_mmap_ro(out, fd, 0, (size_t)len);
 	p_close(fd);
 	return result;
@@ -260,20 +281,31 @@ int git_futils_mkdir_r(const char *path, const char *base, const mode_t mode)
 
 static int _rmdir_recurs_foreach(void *opaque, git_buf *path)
 {
-	int error = GIT_SUCCESS;
 	int force = *(int *)opaque;
 
 	if (git_path_isdir(path->ptr) == true) {
-		error = git_path_direach(path, _rmdir_recurs_foreach, opaque);
-		if (error < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to remove directory `%s`", path->ptr);
-		return p_rmdir(path->ptr);
+		if (git_path_direach(path, _rmdir_recurs_foreach, opaque) < 0)
+			return -1;
+
+		if (p_rmdir(path->ptr) < 0) {
+			giterr_set(GITERR_OS, "Could not remove directory '%s'", path->ptr);
+			return -1;
+		}
 
-	} else if (force) {
-		return p_unlink(path->ptr);
+		return 0;
 	}
 
-	return git__rethrow(error, "Failed to remove directory. `%s` is not empty", path->ptr);
+	if (force) {
+		if (p_unlink(path->ptr) < 0) {
+			giterr_set(GITERR_OS, "Could not remove directory.  File '%s' cannot be removed", path->ptr);
+			return -1;
+		}
+
+		return 0;
+	}
+
+	giterr_set(GITERR_OS, "Could not remove directory. File '%s' still present", path->ptr);
+	return -1;
 }
 
 int git_futils_rmdir_r(const char *path, int force)
@@ -282,7 +314,7 @@ int git_futils_rmdir_r(const char *path, int force)
 	git_buf p = GIT_BUF_INIT;
 
 	error = git_buf_sets(&p, path);
-	if (error == GIT_SUCCESS)
+	if (!error)
 		error = _rmdir_recurs_foreach(&force, &p);
 	git_buf_free(&p);
 	return error;
@@ -328,9 +360,8 @@ static const win32_path *win32_system_root(void)
 		const wchar_t *root_tmpl = L"%PROGRAMFILES%\\Git\\etc\\";
 
 		s_root.len = ExpandEnvironmentStringsW(root_tmpl, NULL, 0);
-
 		if (s_root.len <= 0) {
-			git__throw(GIT_EOSERR, "Failed to expand environment strings");
+			giterr_set(GITERR_OS, "Failed to expand environment strings");
 			return NULL;
 		}
 
@@ -339,7 +370,7 @@ static const win32_path *win32_system_root(void)
 			return NULL;
 
 		if (ExpandEnvironmentStringsW(root_tmpl, s_root.path, s_root.len) != s_root.len) {
-			git__throw(GIT_EOSERR, "Failed to expand environment strings");
+			giterr_set(GITERR_OS, "Failed to expand environment strings");
 			git__free(s_root.path);
 			s_root.path = NULL;
 			return NULL;
@@ -351,7 +382,7 @@ static const win32_path *win32_system_root(void)
 
 static int win32_find_system_file(git_buf *path, const char *filename)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 	const win32_path *root = win32_system_root();
 	size_t len;
 	wchar_t *file_utf16 = NULL, *scan;
@@ -362,8 +393,7 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	/* allocate space for wchar_t path to file */
 	file_utf16 = git__calloc(root->len + len + 2, sizeof(wchar_t));
-	if (!file_utf16)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(file_utf16);
 
 	/* append root + '\\' + filename as wchar_t */
 	memcpy(file_utf16, root->path, root->len * sizeof(wchar_t));
@@ -373,7 +403,7 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	if (gitwin_append_utf16(file_utf16 + root->len - 1, filename, len + 1) !=
 		(int)len + 1) {
-		error = git__throw(GIT_EOSERR, "Failed to build file path");
+		error = -1;
 		goto cleanup;
 	}
 
@@ -389,9 +419,8 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	/* convert to utf8 */
 	if ((file_utf8 = gitwin_from_utf16(file_utf16)) == NULL)
-		error = GIT_ENOMEM;
-
-	if (file_utf8) {
+		error = -1;
+	else {
 		git_path_mkposix(file_utf8);
 		git_buf_attach(path, file_utf8, 0);
 	}
@@ -409,7 +438,7 @@ int git_futils_find_system_file(git_buf *path, const char *filename)
 		return -1;
 
 	if (git_path_exists(path->ptr) == true)
-		return GIT_SUCCESS;
+		return 0;
 
 	git_buf_clear(path);
 
diff --git a/src/fileops.h b/src/fileops.h
index c2ba8ff..6df5653 100644
--- a/src/fileops.h
+++ b/src/fileops.h
@@ -77,18 +77,9 @@ extern int git_futils_mktmp(git_buf *path_out, const char *filename);
 extern int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmode);
 
 /**
- * Open a file readonly and set error if needed
- */
-GIT_INLINE(int) git_futils_open_ro(const char *path)
-{
-	int fd = p_open(path, O_RDONLY);
-	if (fd < 0) {
-		if (errno == ENOENT)
-			fd = GIT_ENOTFOUND;
-		giterr_set(GITERR_OS, "Failed to open '%s'", path);
-	}
-	return fd;
-}
+ * Open a file readonly and set error if needed.
+ */
+extern int git_futils_open_ro(const char *path);
 
 /**
  * Get the filesize in bytes of a file
diff --git a/src/hashtable.c b/src/hashtable.c
index 0364bb5..8e057d4 100644
--- a/src/hashtable.c
+++ b/src/hashtable.c
@@ -258,5 +258,10 @@ uint32_t git_hash__strhash_cb(const void *key, int hash_id)
 		0x7daaab3c
 	};
 
-	return git__hash(key, strlen((const char *)key), hash_seeds[hash_id]);
+	size_t key_len = strlen((const char *)key);
+
+	/* won't take hash of strings longer than 2^31 right now */
+	assert(key_len == (size_t)((int)key_len));
+
+	return git__hash(key, (int)key_len, hash_seeds[hash_id]);
 }
diff --git a/src/hashtable.h b/src/hashtable.h
index e099659..0bab845 100644
--- a/src/hashtable.h
+++ b/src/hashtable.h
@@ -66,7 +66,7 @@ GIT_INLINE(int) git_hashtable_insert(git_hashtable *h, const void *key, void *va
 #define git_hashtable_node_at(nodes, pos) ((git_hashtable_node *)(&nodes[pos]))
 
 #define GIT_HASHTABLE__FOREACH(self,block) { \
-	unsigned int _c; \
+	size_t _c; \
 	git_hashtable_node *_n = (self)->nodes; \
 	for (_c = (self)->size; _c > 0; _c--, _n++)	{ \
 		if (!_n->key) continue; block } }
diff --git a/src/index.c b/src/index.c
index d5410a3..7f5909a 100644
--- a/src/index.c
+++ b/src/index.c
@@ -319,8 +319,7 @@ static int index_entry_init(git_index_entry **entry_out, git_index *index, const
 	if (error < GIT_SUCCESS)
 		return error;
 
-	if (p_lstat(full_path.ptr, &st) < 0) {
-		error = git__throw(GIT_ENOTFOUND, "Failed to initialize entry. '%s' cannot be opened. %s", full_path.ptr, strerror(errno));
+	if ((error = git_path_lstat(full_path.ptr, &st)) < 0) {
 		git_buf_free(&full_path);
 		return error;
 	}
diff --git a/src/indexer.c b/src/indexer.c
index da6495f..6f8bd32 100644
--- a/src/indexer.c
+++ b/src/indexer.c
@@ -133,12 +133,15 @@ int git_indexer_new(git_indexer **out, const char *packname)
 
 	idx->nr_objects = ntohl(idx->hdr.hdr_entries);
 
-	error = git_vector_init(&idx->pack->cache, idx->nr_objects, cache_cmp);
+	/* for now, limit to 2^32 objects */
+	assert(idx->nr_objects == (size_t)((unsigned int)idx->nr_objects));
+
+	error = git_vector_init(&idx->pack->cache, (unsigned int)idx->nr_objects, cache_cmp);
 	if (error < GIT_SUCCESS)
 		goto cleanup;
 
 	idx->pack->has_cache = 1;
-	error = git_vector_init(&idx->objects, idx->nr_objects, objects_cmp);
+	error = git_vector_init(&idx->objects, (unsigned int)idx->nr_objects, objects_cmp);
 	if (error < GIT_SUCCESS)
 		goto cleanup;
 
@@ -319,7 +322,7 @@ int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 	if (error < GIT_SUCCESS)
 		return git__rethrow(error, "Failed to register mwindow file");
 
-	stats->total = idx->nr_objects;
+	stats->total = (unsigned int)idx->nr_objects;
 	stats->processed = processed = 0;
 
 	while (processed < idx->nr_objects) {
@@ -375,7 +378,7 @@ int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 			error = git__rethrow(error, "Failed to open window to read packed data");
 			goto cleanup;
 		}
-		entry->crc = htonl(crc32(entry->crc, packed, entry_size));
+		entry->crc = htonl(crc32(entry->crc, packed, (uInt)entry_size));
 		git_mwindow_close(&w);
 
 		/* Add the object to the list */
diff --git a/src/iterator.c b/src/iterator.c
index 0ce89df..c10b9ff 100644
--- a/src/iterator.c
+++ b/src/iterator.c
@@ -309,7 +309,7 @@ static int workdir_iterator__expand_dir(workdir_iterator *wi)
 
 	/* only push new ignores if this is not top level directory */
 	if (wi->stack->next != NULL) {
-		int slash_pos = git_buf_rfind_next(&wi->path, '/');
+		ssize_t slash_pos = git_buf_rfind_next(&wi->path, '/');
 		(void)git_ignore__push_dir(&wi->ignores, &wi->path.ptr[slash_pos + 1]);
 	}
 
diff --git a/src/mwindow.c b/src/mwindow.c
index e3de070..cde24d1 100644
--- a/src/mwindow.c
+++ b/src/mwindow.c
@@ -203,7 +203,7 @@ unsigned char *git_mwindow_open(
 	git_mwindow_file *mwf,
 	git_mwindow **cursor,
 	git_off_t offset,
-	int extra,
+	size_t extra,
 	unsigned int *left)
 {
 	git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
diff --git a/src/mwindow.h b/src/mwindow.h
index 94bfb5d..0580272 100644
--- a/src/mwindow.h
+++ b/src/mwindow.h
@@ -15,8 +15,8 @@ typedef struct git_mwindow {
 	struct git_mwindow *next;
 	git_map window_map;
 	git_off_t offset;
-	unsigned int last_used;
-	unsigned int inuse_cnt;
+	size_t last_used;
+	size_t inuse_cnt;
 } git_mwindow;
 
 typedef struct git_mwindow_file {
@@ -37,7 +37,7 @@ typedef struct git_mwindow_ctl {
 
 int git_mwindow_contains(git_mwindow *win, git_off_t offset);
 void git_mwindow_free_all(git_mwindow_file *mwf);
-unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, int extra, unsigned int *left);
+unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, size_t extra, unsigned int *left);
 void git_mwindow_scan_lru(git_mwindow_file *mwf, git_mwindow **lru_w, git_mwindow **lru_l);
 int git_mwindow_file_register(git_mwindow_file *mwf);
 void git_mwindow_close(git_mwindow **w_cursor);
diff --git a/src/odb.c b/src/odb.c
index 782a77d..f68d135 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -145,10 +145,8 @@ int git_odb__hashlink(git_oid *out, const char *path)
 	git_off_t size;
 	int result;
 
-	if (p_lstat(path, &st) < 0) {
-		giterr_set(GITERR_OS, "Failed to stat object '%s'", path);
+	if (git_path_lstat(path, &st) < 0)
 		return -1;
-	}
 
 	size = st.st_size;
 
diff --git a/src/path.c b/src/path.c
index d1f094a..0f45d71 100644
--- a/src/path.c
+++ b/src/path.c
@@ -49,7 +49,8 @@ int git_path_basename_r(git_buf *buffer, const char *path)
 	while (startp > path && *(startp - 1) != '/')
 		startp--;
 
-	len = endp - startp +1;
+	/* Cast is safe because max path < max int */
+	len = (int)(endp - startp + 1);
 
 Exit:
 	result = len;
@@ -96,7 +97,8 @@ int git_path_dirname_r(git_buf *buffer, const char *path)
 		endp--;
 	} while (endp > path && *endp == '/');
 
-	len = endp - path +1;
+	/* Cast is safe because max path < max int */
+	len = (int)(endp - path + 1);
 
 #ifdef GIT_WIN32
 	/* Mimic unix behavior where '/.git' returns '/': 'C:/.git' will return
@@ -146,7 +148,7 @@ char *git_path_basename(const char *path)
 const char *git_path_topdir(const char *path)
 {
 	size_t len;
-	int i;
+	ssize_t i;
 
 	assert(path);
 	len = strlen(path);
@@ -154,7 +156,7 @@ const char *git_path_topdir(const char *path)
 	if (!len || path[len - 1] != '/')
 		return NULL;
 
-	for (i = len - 2; i >= 0; --i)
+	for (i = (ssize_t)len - 2; i >= 0; --i)
 		if (path[i] == '/')
 			break;
 
@@ -235,7 +237,7 @@ int git__percent_decode(git_buf *decoded_out, const char *input)
 	int len, hi, lo, i;
 	assert(decoded_out && input);
 
-	len = strlen(input);
+	len = (int)strlen(input);
 	git_buf_clear(decoded_out);
 
 	for(i = 0; i < len; i++)
@@ -281,7 +283,7 @@ int git_path_fromurl(git_buf *local_path_out, const char *file_url)
 		return error_invalid_local_file_uri(file_url);
 
 	offset += 7;
-	len = strlen(file_url);
+	len = (int)strlen(file_url);
 
 	if (offset < len && file_url[offset] == '/')
 		offset++;
@@ -381,6 +383,18 @@ bool git_path_isfile(const char *path)
 	return S_ISREG(st.st_mode) != 0;
 }
 
+int git_path_lstat(const char *path, struct stat *st)
+{
+	int err = 0;
+
+	if (p_lstat(path, st) < 0) {
+		err = (errno == ENOENT) ? GIT_ENOTFOUND : -1;
+		giterr_set(GITERR_OS, "Failed to stat file '%s'", path);
+	}
+
+	return err;
+}
+
 static bool _check_dir_contents(
 	git_buf *dir,
 	const char *sub,
@@ -600,16 +614,9 @@ int git_path_dirload_with_stat(
 		memmove(ps->path, ps, path_len + 1);
 		ps->path_len = path_len;
 
-		if (git_buf_joinpath(&full, full.ptr, ps->path) < 0) {
-			error = -1;
+		if ((error = git_buf_joinpath(&full, full.ptr, ps->path)) < 0 ||
+			(error = git_path_lstat(full.ptr, &ps->st)) < 0)
 			break;
-		}
-
-		if (p_lstat(full.ptr, &ps->st) < 0) {
-			giterr_set(GITERR_OS, "Failed to stat file '%s'", full.ptr);
-			error = -1;
-			break;
-		}
 
 		git_buf_truncate(&full, prefix_len);
 
diff --git a/src/path.h b/src/path.h
index e885d87..3cf7394 100644
--- a/src/path.h
+++ b/src/path.h
@@ -130,6 +130,11 @@ extern bool git_path_isdir(const char *path);
 extern bool git_path_isfile(const char *path);
 
 /**
+ * Stat a file and/or link and set error if needed.
+ */
+extern int git_path_lstat(const char *path, struct stat *st);
+
+/**
  * Check if the parent directory contains the item.
  *
  * @param dir Directory to check.
diff --git a/src/posix.c b/src/posix.c
index 9d96d30..9778809 100644
--- a/src/posix.c
+++ b/src/posix.c
@@ -34,9 +34,9 @@ int p_getcwd(char *buffer_out, size_t size)
 		return -1;
 
 	git_path_mkposix(buffer_out);
-	git_path_string_to_dir(buffer_out, size);	//Ensure the path ends with a trailing slash
+	git_path_string_to_dir(buffer_out, size); /* append trailing slash */
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int p_rename(const char *from, const char *to)
diff --git a/src/repository.c b/src/repository.c
index 7d7b3c4..99eee52 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -377,17 +377,15 @@ void git_repository_set_index(git_repository *repo, git_index *index)
 
 static int retrieve_device(dev_t *device_out, const char *path)
 {
+	int error;
 	struct stat path_info;
 
 	assert(device_out);
 
-	if (p_lstat(path, &path_info)) {
-		giterr_set(GITERR_OS, "Failed to retrieve file information: %s", strerror(errno));
-		return -1;
-	}
+	if ((error = git_path_lstat(path, &path_info)) == 0)
+		*device_out = path_info.st_dev;
 
-	*device_out = path_info.st_dev;
-	return 0;
+	return error;
 }
 
 /*
diff --git a/src/win32/dir.c b/src/win32/dir.c
index 035e2b6..bc3d40f 100644
--- a/src/win32/dir.c
+++ b/src/win32/dir.c
@@ -27,8 +27,8 @@ static int init_filter(char *filter, size_t n, const char *dir)
 git__DIR *git__opendir(const char *dir)
 {
 	char filter[4096];
-	wchar_t* filter_w;
-	git__DIR *new;
+	wchar_t* filter_w = NULL;
+	git__DIR *new = NULL;
 
 	if (!dir || !init_filter(filter, sizeof(filter), dir))
 		return NULL;
@@ -37,25 +37,29 @@ git__DIR *git__opendir(const char *dir)
 	if (!new)
 		return NULL;
 
-	new->dir = git__malloc(strlen(dir)+1);
-	if (!new->dir) {
-		git__free(new);
-		return NULL;
-	}
-	strcpy(new->dir, dir);
+	new->dir = git__strdup(dir);
+	if (!new->dir)
+		goto fail;
 
 	filter_w = gitwin_to_utf16(filter);
+	if (!filter_w)
+		goto fail;
+
 	new->h = FindFirstFileW(filter_w, &new->f);
 	git__free(filter_w);
 
 	if (new->h == INVALID_HANDLE_VALUE) {
-		git__free(new->dir);
-		git__free(new);
-		return NULL;
+		giterr_set(GITERR_OS, "Could not open directory '%s'", dir);
+		goto fail;
 	}
-	new->first = 1;
 
+	new->first = 1;
 	return new;
+
+fail:
+	git__free(new->dir);
+	git__free(new);
+	return NULL;
 }
 
 int git__readdir_ext(
@@ -67,22 +71,32 @@ int git__readdir_ext(
 	if (!d || !entry || !result || d->h == INVALID_HANDLE_VALUE)
 		return -1;
 
+	*result = NULL;
+
 	if (d->first)
 		d->first = 0;
 	else if (!FindNextFileW(d->h, &d->f)) {
-		*result = NULL;
-		return 0;
+		if (GetLastError() == ERROR_NO_MORE_FILES)
+			return 0;
+		giterr_set(GITERR_OS, "Could not read from directory '%s'", d->dir);
+		return -1;
 	}
 
 	if (wcslen(d->f.cFileName) >= sizeof(entry->d_name))
 		return -1;
 
 	entry->d_ino = 0;
-	WideCharToMultiByte(
+
+	if (WideCharToMultiByte(
 		gitwin_get_codepage(), 0, d->f.cFileName, -1,
-		entry->d_name, GIT_PATH_MAX, NULL, NULL);
+		entry->d_name, GIT_PATH_MAX, NULL, NULL) == 0)
+	{
+		giterr_set(GITERR_OS, "Could not convert filename to UTF-8");
+		return -1;
+	}
 
 	*result = entry;
+
 	if (is_dir != NULL)
 		*is_dir = ((d->f.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0);
 
@@ -102,32 +116,40 @@ void git__rewinddir(git__DIR *d)
 	char filter[4096];
 	wchar_t* filter_w;
 
-	if (d) {
-		if (d->h != INVALID_HANDLE_VALUE)
-			FindClose(d->h);
+	if (!d)
+		return;
+
+	if (d->h != INVALID_HANDLE_VALUE) {
+		FindClose(d->h);
 		d->h = INVALID_HANDLE_VALUE;
 		d->first = 0;
+	}
 
-		if (init_filter(filter, sizeof(filter), d->dir)) {
-			filter_w = gitwin_to_utf16(filter);
-			d->h = FindFirstFileW(filter_w, &d->f);
-			git__free(filter_w);
+	if (!init_filter(filter, sizeof(filter), d->dir) ||
+		(filter_w = gitwin_to_utf16(filter)) == NULL)
+		return;
 
-			if (d->h != INVALID_HANDLE_VALUE)
-				d->first = 1;
-		}
-	}
+	d->h = FindFirstFileW(filter_w, &d->f);
+	git__free(filter_w);
+
+	if (d->h == INVALID_HANDLE_VALUE)
+		giterr_set(GITERR_OS, "Could not open directory '%s'", d->dir);
+	else
+		d->first = 1;
 }
 
 int git__closedir(git__DIR *d)
 {
-	if (d) {
-		if (d->h != INVALID_HANDLE_VALUE)
-			FindClose(d->h);
-		if (d->dir)
-			git__free(d->dir);
-		git__free(d);
+	if (!d)
+		return 0;
+
+	if (d->h != INVALID_HANDLE_VALUE) {
+		FindClose(d->h);
+		d->h = INVALID_HANDLE_VALUE;
 	}
+	git__free(d->dir);
+	d->dir = NULL;
+	git__free(d);
 	return 0;
 }
 
diff --git a/src/win32/posix_w32.c b/src/win32/posix_w32.c
index a915898..c6b36a8 100644
--- a/src/win32/posix_w32.c
+++ b/src/win32/posix_w32.c
@@ -17,10 +17,11 @@ int p_unlink(const char *path)
 	int ret = 0;
 	wchar_t* buf;
 
-	buf = gitwin_to_utf16(path);
-	_wchmod(buf, 0666);
-	ret = _wunlink(buf);
-	git__free(buf);
+	if ((buf = gitwin_to_utf16(path)) != NULL) {
+		_wchmod(buf, 0666);
+		ret = _wunlink(buf);
+		git__free(buf);
+	}
 
 	return ret;
 }
@@ -60,6 +61,8 @@ static int do_lstat(const char *file_name, struct stat *buf)
 {
 	WIN32_FILE_ATTRIBUTE_DATA fdata;
 	wchar_t* fbuf = gitwin_to_utf16(file_name);
+	if (!fbuf)
+		return -1;
 
 	if (GetFileAttributesExW(fbuf, GetFileExInfoStandard, &fdata)) {
 		int fMode = S_IREAD;
@@ -87,54 +90,43 @@ static int do_lstat(const char *file_name, struct stat *buf)
 		buf->st_ctime = filetime_to_time_t(&(fdata.ftCreationTime));
 
 		git__free(fbuf);
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	git__free(fbuf);
-
-	switch (GetLastError()) {
-		case ERROR_ACCESS_DENIED:
-		case ERROR_SHARING_VIOLATION:
-		case ERROR_LOCK_VIOLATION:
-		case ERROR_SHARING_BUFFER_EXCEEDED:
-			return GIT_EOSERR;
-
-		case ERROR_BUFFER_OVERFLOW:
-		case ERROR_NOT_ENOUGH_MEMORY:
-			return GIT_ENOMEM;
-
-		default:
-			return GIT_EINVALIDPATH;
-	}
+	return -1;
 }
 
 int p_lstat(const char *file_name, struct stat *buf)
 {
-	int namelen, error;
-	char alt_name[GIT_PATH_MAX];
+	int error;
+	size_t namelen;
+	char *alt_name;
 
-	if ((error = do_lstat(file_name, buf)) == GIT_SUCCESS)
-		return GIT_SUCCESS;
+	if (do_lstat(file_name, buf) == 0)
+		return 0;
 
 	/* if file_name ended in a '/', Windows returned ENOENT;
 	 * try again without trailing slashes
 	 */
-	if (error != GIT_EINVALIDPATH)
-		return git__throw(GIT_EOSERR, "Failed to lstat file");
-
 	namelen = strlen(file_name);
 	if (namelen && file_name[namelen-1] != '/')
-		return git__throw(GIT_EOSERR, "Failed to lstat file");
+		return -1;
 
 	while (namelen && file_name[namelen-1] == '/')
 		--namelen;
 
-	if (!namelen || namelen >= GIT_PATH_MAX)
-		return git__throw(GIT_ENOMEM, "Failed to lstat file");
+	if (!namelen)
+		return -1;
+
+	alt_name = git__strndup(file_name, namelen);
+	if (!alt_name)
+		return -1;
+
+	error = do_lstat(alt_name, buf);
 
-	memcpy(alt_name, file_name, namelen);
-	alt_name[namelen] = 0;
-	return do_lstat(alt_name, buf);
+	git__free(alt_name);
+	return error;
 }
 
 int p_readlink(const char *link, char *target, size_t target_len)
@@ -145,6 +137,9 @@ int p_readlink(const char *link, char *target, size_t target_len)
 	DWORD dwRet;
 	wchar_t* link_w;
 	wchar_t* target_w;
+	int error = 0;
+
+	assert(link && target && target_len > 0);
 
 	/*
 	 * Try to load the pointer to pGetFinalPath dynamically, because
@@ -156,12 +151,15 @@ int p_readlink(const char *link, char *target, size_t target_len)
 		if (library != NULL)
 			pGetFinalPath = (fpath_func)GetProcAddress(library, "GetFinalPathNameByHandleW");
 
-		if (pGetFinalPath == NULL)
-			return git__throw(GIT_EOSERR,
+		if (pGetFinalPath == NULL) {
+			giterr_set(GITERR_OS,
 				"'GetFinalPathNameByHandleW' is not available in this platform");
+			return -1;
+		}
 	}
 
 	link_w = gitwin_to_utf16(link);
+	GITERR_CHECK_ALLOC(link_w);
 
 	hFile = CreateFileW(link_w,			// file to open
 			GENERIC_READ,			// open for reading
@@ -173,50 +171,49 @@ int p_readlink(const char *link, char *target, size_t target_len)
 
 	git__free(link_w);
 
-	if (hFile == INVALID_HANDLE_VALUE)
-		return GIT_EOSERR;
-
-	if (target_len <= 0) {
-		return GIT_EINVALIDARGS;
+	if (hFile == INVALID_HANDLE_VALUE) {
+		giterr_set(GITERR_OS, "Cannot open '%s' for reading", link);
+		return -1;
 	}
 
 	target_w = (wchar_t*)git__malloc(target_len * sizeof(wchar_t));
+	GITERR_CHECK_ALLOC(target_w);
 
 	dwRet = pGetFinalPath(hFile, target_w, target_len, 0x0);
-	if (dwRet >= target_len) {
-		git__free(target_w);
-		CloseHandle(hFile);
-		return GIT_ENOMEM;
-	}
-
-	if (!WideCharToMultiByte(CP_UTF8, 0, target_w, -1, target, target_len * sizeof(char), NULL, NULL)) {
-		git__free(target_w);
-		return GIT_EOSERR;
-	}
+	if (dwRet == 0 ||
+		dwRet >= target_len ||
+		!WideCharToMultiByte(CP_UTF8, 0, target_w, -1, target,
+			target_len * sizeof(char), NULL, NULL))
+		error = -1;
 
 	git__free(target_w);
 	CloseHandle(hFile);
 
-	if (dwRet > 4) {
-		/* Skip first 4 characters if they are "\\?\" */
-		if (target[0] == '\\' && target[1] == '\\' && target[2] == '?' && target[3] == '\\') {
-			char tmp[GIT_PATH_MAX];
-			unsigned int offset = 4;
-			dwRet -= 4;
-
-			/* \??\UNC\ */
-			if (dwRet > 7 && target[4] == 'U' && target[5] == 'N' && target[6] == 'C') {
-				offset += 2;
-				dwRet -= 2;
-				target[offset] = '\\';
-			}
-
-			memcpy(tmp, target + offset, dwRet);
-			memcpy(target, tmp, dwRet);
+	if (error)
+		return error;
+
+	/* Skip first 4 characters if they are "\\?\" */
+	if (dwRet > 4 &&
+		target[0] == '\\' && target[1] == '\\' &&
+		target[2] == '?' && target[3] == '\\')
+	{
+		unsigned int offset = 4;
+		dwRet -= 4;
+
+		/* \??\UNC\ */
+		if (dwRet > 7 &&
+			target[4] == 'U' && target[5] == 'N' && target[6] == 'C')
+		{
+			offset += 2;
+			dwRet -= 2;
+			target[offset] = '\\';
 		}
+
+		memmove(target, target + offset, dwRet);
 	}
 
 	target[dwRet] = '\0';
+
 	return dwRet;
 }
 
@@ -224,8 +221,9 @@ int p_open(const char *path, int flags)
 {
 	int fd;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 	fd = _wopen(buf, flags | _O_BINARY);
-
 	git__free(buf);
 	return fd;
 }
@@ -234,8 +232,9 @@ int p_creat(const char *path, mode_t mode)
 {
 	int fd;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 	fd = _wopen(buf, _O_WRONLY | _O_CREAT | _O_TRUNC | _O_BINARY, mode);
-
 	git__free(buf);
 	return fd;
 }
@@ -243,15 +242,15 @@ int p_creat(const char *path, mode_t mode)
 int p_getcwd(char *buffer_out, size_t size)
 {
 	wchar_t* buf = (wchar_t*)git__malloc(sizeof(wchar_t) * (int)size);
+	int ret;
+
 	_wgetcwd(buf, (int)size);
 
-	if (!WideCharToMultiByte(CP_UTF8, 0, buf, -1, buffer_out, size, NULL, NULL)) {
-		git__free(buf);
-		return GIT_EOSERR;
-	}
+	ret = WideCharToMultiByte(
+		CP_UTF8, 0, buf, -1, buffer_out, size, NULL, NULL);
 
 	git__free(buf);
-	return GIT_SUCCESS;
+	return !ret ? -1 : 0;
 }
 
 int p_stat(const char* path, struct stat* buf)
@@ -262,8 +261,10 @@ int p_stat(const char* path, struct stat* buf)
 int p_chdir(const char* path)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wchdir(buf);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wchdir(buf);
 	git__free(buf);
 	return ret;
 }
@@ -271,8 +272,10 @@ int p_chdir(const char* path)
 int p_chmod(const char* path, mode_t mode)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wchmod(buf, mode);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wchmod(buf, mode);
 	git__free(buf);
 	return ret;
 }
@@ -280,8 +283,10 @@ int p_chmod(const char* path, mode_t mode)
 int p_rmdir(const char* path)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wrmdir(buf);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wrmdir(buf);
 	git__free(buf);
 	return ret;
 }
@@ -290,11 +295,13 @@ int p_hide_directory__w32(const char *path)
 {
 	int res;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 
 	res = SetFileAttributesW(buf, FILE_ATTRIBUTE_HIDDEN);
 	git__free(buf);
-	
-	return (res != 0) ?  GIT_SUCCESS : GIT_ERROR; /* MSDN states a "non zero" value indicates a success */
+
+	return (res != 0) ? 0 : -1; /* MSDN states a "non zero" value indicates a success */
 }
 
 char *p_realpath(const char *orig_path, char *buffer)
@@ -303,6 +310,9 @@ char *p_realpath(const char *orig_path, char *buffer)
 	wchar_t* orig_path_w = gitwin_to_utf16(orig_path);
 	wchar_t* buffer_w = (wchar_t*)git__malloc(GIT_PATH_MAX * sizeof(wchar_t));
 
+	if (!orig_path_w || !buffer_w)
+		return NULL;
+
 	ret = GetFullPathNameW(orig_path_w, GIT_PATH_MAX, buffer_w, NULL);
 	git__free(orig_path_w);
 
@@ -365,10 +375,10 @@ int p_mkstemp(char *tmp_path)
 {
 #if defined(_MSC_VER)
 	if (_mktemp_s(tmp_path, strlen(tmp_path) + 1) != 0)
-		return GIT_EOSERR;
+		return -1;
 #else
 	if (_mktemp(tmp_path) == NULL)
-		return GIT_EOSERR;
+		return -1;
 #endif
 
 	return p_creat(tmp_path, 0744);
@@ -377,15 +387,17 @@ int p_mkstemp(char *tmp_path)
 int p_setenv(const char* name, const char* value, int overwrite)
 {
 	if (overwrite != 1)
-		return EINVAL;
+		return -1;
 
-	return (SetEnvironmentVariableA(name, value) == 0 ? GIT_EOSERR : GIT_SUCCESS);
+	return (SetEnvironmentVariableA(name, value) == 0 ? -1 : 0);
 }
 
 int p_access(const char* path, mode_t mode)
 {
 	wchar_t *buf = gitwin_to_utf16(path);
 	int ret;
+	if (!buf)
+		return -1;
 
 	ret = _waccess(buf, mode);
 	git__free(buf);
@@ -393,13 +405,16 @@ int p_access(const char* path, mode_t mode)
 	return ret;
 }
 
-extern int p_rename(const char *from, const char *to)
+int p_rename(const char *from, const char *to)
 {
 	wchar_t *wfrom = gitwin_to_utf16(from);
 	wchar_t *wto = gitwin_to_utf16(to);
 	int ret;
 
-	ret = MoveFileExW(wfrom, wto, MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED) ? GIT_SUCCESS : GIT_EOSERR;
+	if (!wfrom || !wto)
+		return -1;
+
+	ret = MoveFileExW(wfrom, wto, MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED) ? 0 : -1;
 
 	git__free(wfrom);
 	git__free(wto);
diff --git a/src/win32/pthread.c b/src/win32/pthread.c
index 3db5368..3a186c8 100644
--- a/src/win32/pthread.c
+++ b/src/win32/pthread.c
@@ -7,13 +7,16 @@
 
 #include "pthread.h"
 
-int pthread_create(pthread_t *GIT_RESTRICT thread,
-					const pthread_attr_t *GIT_RESTRICT attr,
-					void *(*start_routine)(void*), void *GIT_RESTRICT arg)
+int pthread_create(
+	pthread_t *GIT_RESTRICT thread,
+	const pthread_attr_t *GIT_RESTRICT attr,
+	void *(*start_routine)(void*),
+	void *GIT_RESTRICT arg)
 {
 	GIT_UNUSED(attr);
-	*thread = (pthread_t) CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)start_routine, arg, 0, NULL);
-	return *thread ? GIT_SUCCESS : git__throw(GIT_EOSERR, "Failed to create pthread");
+	*thread = (pthread_t) CreateThread(
+		NULL, 0, (LPTHREAD_START_ROUTINE)start_routine, arg, 0, NULL);
+	return *thread ? 0 : -1;
 }
 
 int pthread_join(pthread_t thread, void **value_ptr)
diff --git a/src/win32/utf-conv.c b/src/win32/utf-conv.c
index 3c8be81..f00f5be 100644
--- a/src/win32/utf-conv.c
+++ b/src/win32/utf-conv.c
@@ -33,14 +33,14 @@ wchar_t* gitwin_to_utf16(const char* str)
 	wchar_t* ret;
 	int cb;
 
-	if (!str) {
+	if (!str)
 		return NULL;
-	}
 
 	cb = strlen(str) * sizeof(wchar_t);
 	if (cb == 0) {
 		ret = (wchar_t*)git__malloc(sizeof(wchar_t));
-		ret[0] = 0;
+		if (ret)
+			ret[0] = 0;
 		return ret;
 	}
 
@@ -48,8 +48,11 @@ wchar_t* gitwin_to_utf16(const char* str)
 	cb += sizeof(wchar_t);
 
 	ret = (wchar_t*)git__malloc(cb);
+	if (!ret)
+		return NULL;
 
 	if (MultiByteToWideChar(_active_codepage, 0, str, -1, ret, cb) == 0) {
+		giterr_set(GITERR_OS, "Could not convert string to UTF-16");
 		git__free(ret);
 		ret = NULL;
 	}
@@ -59,7 +62,10 @@ wchar_t* gitwin_to_utf16(const char* str)
 
 int gitwin_append_utf16(wchar_t *buffer, const char *str, size_t len)
 {
-	return MultiByteToWideChar(_active_codepage, 0, str, -1, buffer, len);
+	int result = MultiByteToWideChar(_active_codepage, 0, str, -1, buffer, len);
+	if (result == 0)
+		giterr_set(GITERR_OS, "Could not convert string to UTF-16");
+	return result;
 }
 
 char* gitwin_from_utf16(const wchar_t* str)
@@ -74,7 +80,8 @@ char* gitwin_from_utf16(const wchar_t* str)
 	cb = wcslen(str) * sizeof(char);
 	if (cb == 0) {
 		ret = (char*)git__malloc(sizeof(char));
-		ret[0] = 0;
+		if (ret)
+			ret[0] = 0;
 		return ret;
 	}
 
@@ -82,8 +89,11 @@ char* gitwin_from_utf16(const wchar_t* str)
 	cb += sizeof(char);
 
 	ret = (char*)git__malloc(cb);
+	if (!ret)
+		return NULL;
 
 	if (WideCharToMultiByte(_active_codepage, 0, str, -1, ret, cb, NULL, NULL) == 0) {
+		giterr_set(GITERR_OS, "Could not convert string to UTF-8");
 		git__free(ret);
 		ret = NULL;
 	}