This saves several words in the hash table object at the cost of an
indirection at runtime.  This seems to be a gain in overall
performance.

FIXME: We cache hash test objects in a rather clumsy way. A better
solution is sought.

* src/lisp.h (struct Lisp_Hash_Table): Use a pointer to the test
struct.  All references adapted.
* src/alloc.c (garbage_collect):
* src/fns.c (struct hash_table_user_test, hash_table_user_tests)
(mark_fns, get_hash_table_user_test): New state for caching test
structs, and functions managing it.

This improves performance in several ways.  Separate functions are
used depending on whether the caller has a hash value computed or not.

* src/fns.c (hash_lookup_with_hash, hash_lookup_get_hash): New.
(hash_lookup): Remove hash return argument.
All callers adapted.

This improves typing, saves pointless tagging and untagging, and
prepares for further changes. The new typedef hash_hash_t is an alias
for EMACS_UINT, and hash values are still limited to the fixnum range.
We now use hash_unused instead of Qnil to mark unused entries.

* src/lisp.h (hash_hash_t): New typedef for EMACS_UINT.
(hash_unused): New constant.
(struct hash_table_test): `hashfn` now returns
hash_hash_t.  All callers and implementations changed.
(struct Lisp_Hash_Table): Retype hash vector to an array of
hash_hash_t.  All code using it changed accordingly.
(HASH_HASH, hash_from_key):
* src/fns.c (set_hash_index_slot, hash_index_index)
(hash_lookup_with_hash, hash_lookup_get_hash, hash_put):
(hash_lookup, hash_put): Retype hash value arguments
and return values.  All callers adapted.

These parameters have no visible semantics and are hardly ever used,
so just use the default values for all hash tables.  This saves
memory, shrinks the external representation, and will improve
performance.

* src/fns.c (std_rehash_size, std_rehash_threshold): New.
(hash_index_size): Use std_rehash_threshold.  Remove table argument.
All callers updated.
(make_hash_table): Remove rehash_size and rehash_threshold args.
All callers updated.
(maybe_resize_hash_table)
(Fhash_table_rehash_size, Fhash_table_rehash_threshold):
Use std_rehash_size and std_rehash_threshold.
(Fmake_hash_table): Ignore :rehash-size and :rehash-threshold args.
* src/lisp.h (struct Lisp_Hash_Table):
Remove rehash_size and rehash_threshold fields.
(DEFAULT_REHASH_THRESHOLD, DEFAULT_REHASH_SIZE): Remove.
* src/lread.c (hash_table_from_plist): Don't read rehash-size or
rehash-threshold.
(syms_of_lread): Remove unused symbols.
* src/print.c (print_object): Don't print rehash-size or rehash-threshold.
* src/pdumper.c (dump_hash_table): Don't dump removed fields.

This takes less space (saves an entire word) and is more type-safe.
No change in behaviour.

* src/lisp.h (hash_table_weakness_t): New.
(struct Lisp_Hash_Table): Replace Lisp object `weak` with enum
`weakness`.
* src/fns.c
(keep_entry_p, hash_table_weakness_symbol): New.
(make_hash_table): Retype argument.  All callers updated.
(sweep_weak_table, Fmake_hash_table, Fhash_table_weakness):
* src/alloc.c (purecopy_hash_table, purecopy, process_mark_stack):
* src/pdumper.c (dump_hash_table):
* src/print.c (print_object): Use retyped field.

It's not a meaningful part of the external representation.
This allows for faster printing and reading, smaller
external representation, and less memory consumption.

* src/print.c (print_object): Omit size.
* src/lread.c (hash_table_from_plist): Take size from the data.

* src/lread.c (read_filtered_event): Disable text conversion if
merely ascii_required.  (bug#65370)

* configure.ac (ANDROID_STUBIFY): Add androidvfs.o when building
libemacs.so.
* doc/emacs/android.texi (Android): Add `Android Document Providers'.
(Android Startup): Update the location of the content identifier
directory.
(Android File System): Describe access to document provider
directories.
(Android Document Providers): New node.
* doc/emacs/emacs.texi (Top): Update the menu for the Android
appendix.
* java/Makefile.in (filename, install_temp/assets/build_info): Make
directory-tree depend on build_info.
* java/org/gnu/emacs/EmacsActivity.java (onActivityResult): New
function.  When a document tree is accepted, persist access to it.
* java/org/gnu/emacs/EmacsDirectoryEntry.java (EmacsDirectoryEntry):
New struct.
* java/org/gnu/emacs/EmacsOpenActivity.java (checkReadableOrCopy): Use
EmacsService.buildContentName.
* java/org/gnu/emacs/EmacsService.java (getEmacsView, openContentUri)
(checkContentUri): Remove excessive debug logging.
(buildContentName, getDocumentAuthorities, requestDirectoryAccess)
(getDocumentTrees, decodeFileName, documentIdFromName, getTreeUri)
(statDocument, accessDocument, openDocumentDirectory, readDirectoryEntry)
(openDocument, createDocument): New functions.

* lib-src/asset-directory-tool.c: Improve commentary by illustrating
the difference between directory and ordinary files.

* src/android.c (ANDROID_THROW, enum android_fd_table_entry_flags)
(struct android_emacs_service, android_extract_long)
(android_scan_directory_tree, android_is_directory)
(android_get_asset_name, android_url_encode, android_content_name_p)
(android_get_content_name, android_check_content_access, android_fstat)
(android_fstatat, android_file_access_p, android_hack_asset_fd_fallback)
(android_detect_ashmem, android_hack_asset_fd, android_close_on_exec)
(android_open, android_close, android_fclose, android_create_lib_link)
(android_faccessat, struct android_dir, android_opendir, android_dirfd)
(android_readdir, android_closedir, android_lookup_asset_directory_fd)
(android_exception_check_3, android_get_current_api_level)
(android_open_asset, android_close_asset, android_asset_read_quit)
(android_asset_read, android_asset_lseek, android_asset_fstat): Move
content and asset related functions to androidvfs.c.
(android_init_emacs_service): Obtain handles for new JNI functions.
(initEmacsParams): Initialize the VFS layer.
(android_request_directory_access): New function.
(android_display_toast): Remove unused function.

* src/android.h (android_get_current_api_level): Assume that
this function never returns less than __ANDROID_API__.
(struct android_emacs_service): Move `struct
android_emacs_service' here.

* src/androidfns.c (Fandroid_request_directory_access): New
interactive function.
(syms_of_androidfns): Register new subr.

* src/androidvfs.c (struct android_vdir, struct android_vops)
(struct android_vnode, struct android_special_vnode)
(enum android_vnode_type, struct android_cursor_class)
(struct emacs_directory_entry_class)
(struct android_parcel_file_descriptor_class)
(android_init_cursor_class, android_init_entry_class)
(android_init_fd_class, android_vfs_canonicalize_name)
(struct android_unix_vnode, struct android_unix_vdir, unix_vfs_ops)
(android_unix_name, android_unix_vnode, android_unix_open)
(android_unix_close, android_unix_unlink, android_unix_symlink)
(android_unix_rmdir, android_unix_rename, android_unix_stat)
(android_unix_access, android_unix_mkdir, android_unix_readdir)
(android_unix_closedir, android_unix_dirfd, android_unix_opendir)
(android_extract_long, android_scan_directory_tree)
(android_is_directory, android_init_assets)
(android_hack_asset_fd_fallback, android_detect_ashmem)
(android_hack_asset_fd, struct android_afs_vnode)
(struct android_afs_vdir, struct android_afs_open_fd, afs_vfs_ops)
(android_afs_name, android_afs_initial, android_close_on_exec)
(android_afs_open, android_afs_close, android_afs_unlink)
(android_afs_symlink, android_afs_rmdir, android_afs_rename)
(android_afs_stat, android_afs_access, android_afs_mkdir)
(android_afs_readdir, android_afs_closedir, android_afs_dirfd)
(android_afs_opendir, android_afs_get_directory_name)
(struct android_content_vdir, content_vfs_ops)
(content_directory_contents, android_content_name)
(android_content_open, android_content_close)
(android_content_unlink, android_content_symlink)
(android_content_rmdir, android_content_rename)
(android_content_stat, android_content_access)
(android_content_mkdir, android_content_readdir)
(android_content_closedir, android_content_dirfd)
(android_content_opendir, android_content_get_directory_name)
(android_content_initial, android_get_content_name)
(android_check_content_access, struct android_authority_vnode)
(authority_vfs_ops, android_authority_name, android_authority_open)
(android_authority_close, android_authority_unlink)
(android_authority_symlink, android_authority_rmdir)
(android_authority_rename, android_authority_stat)
(android_authority_access, android_authority_mkdir)
(android_authority_opendir, android_authority_initial)
(struct android_saf_root_vnode, struct android_saf_root_vdir)
(saf_root_vfs_ops, android_saf_root_name, android_saf_root_open)
(android_saf_root_close, android_saf_root_unlink)
(android_saf_root_symlink, android_saf_root_rmdir)
(android_saf_root_rename, android_saf_root_stat)
(android_saf_root_access, android_saf_root_mkdir)
(android_saf_root_readdir, android_saf_root_closedir)
(android_saf_root_dirfd, android_saf_root_opendir)
(android_saf_root_initial, android_saf_root_get_directory)
(android_saf_stat, android_saf_access)
(struct android_saf_tree_vnode, struct android_saf_tree_vdir)
(saf_tree_vfs_ops, android_document_id_from_name)
(android_saf_tree_name, android_saf_tree_open)
(android_saf_tree_close, android_saf_tree_unlink)
(android_saf_tree_symlink, android_saf_tree_rmdir)
(android_saf_tree_rename, android_saf_tree_stat)
(android_saf_tree_access, android_saf_tree_mkdir)
(android_saf_tree_opendir_1, android_saf_tree_readdir)
(android_saf_tree_closedir, android_saf_tree_dirfd)
(android_saf_tree_opendir, android_saf_tree_from_name)
(android_saf_tree_get_directory, android_saf_file_vnode)
(saf_file_vfs_ops, android_saf_file_name, android_saf_file_open)
(android_saf_file_unlink, android_saf_file_rmdir)
(android_saf_file_opendir, android_close_parcel_fd)
(android_saf_new_vnode, android_saf_new_name, android_saf_new_open)
(android_saf_new_unlink, android_saf_new_symlink)
(android_saf_new_rmdir, android_saf_new_rename)
(android_saf_new_stat, android_saf_new_access)
(android_saf_new_mkdir, android_saf_new_opendir, root_vfs_ops)
(special_vnodes, android_root_name, android_name_file)
(android_vfs_init, android_open, android_unlink, android_symlink)
(android_rmdir, android_mkdir, android_renameat_noreplace)
(android_rename, android_fstat, android_fstatat_1, android_fstatat)
(android_faccessat, android_fdopen, android_close, android_fclose)
(android_open_asset, android_close_asset, android_asset_read_quit)
(android_asset_read, android_asset_lseek, android_asset_fstat)
(android_opendir, android_dirfd, android_readdir)
(android_closedir): Move file system emulation routines here.
Introduce a new ``VFS'' layer for translating between
Emacs-specific file names and the various disparate interfaces
for accessing files on Android.

* src/callproc.c (delete_temp_file):
* src/charset.c (load_charset_map_from_file):
* src/dired.c:
* src/emacs.c (Fkill_emacs):
* src/fileio.c (check_mutable_filename, Fcopy_file)
(Fmake_directory_internal, Fdelete_directory_internal)
(Fdelete_file, Frename_file, Fadd_name_to_file)
(Fmake_symbolic_link, file_accessible_directory_p, Fset_file_modes)
(Fset_file_times, write_region):
* src/filelock.c (get_boot_time, rename_lock_file)
(create_lock_file, current_lock_owner, unlock_file):
* src/image.c (slurp_file, png_load_body, jpeg_load_body):
* src/keyboard.c (Fopen_dribble_file):
* src/lisp.h:
* src/lread.c (Fload):
* src/process.c (handle_child_signal):
* src/sysdep.c (init_standard_fds, emacs_fopen, emacs_fdopen)
(emacs_unlink, emacs_symlink, emacs_rmdir, emacs_mkdir)
(emacs_renameat_noreplace, emacs_rename):
* src/term.c (Fresume_tty, init_tty): Use and add new wrappers
for fopen, fdopen, unlink, symlink, rmdir, mkdir,
renameat_norepalce and rename.

Nowadays .elc files routinely contain tokens like 1.0e+INF and
0.0e+NaN that do not work on antiques like the VAX that lack IEEE fp.
Port Emacs to these platforms, by treating infinities as extreme
values and NaNs as strings that trap if used numerically.
* src/lread.c (INFINITY): Default to HUGE_VAL if non-IEEE.
(not_a_number) [!IEEE_FLOATING_POINT]: New static array.
(syms_of_lread) [!IEEE_FLOATING_POINT]: Initialize it.
(read0): Report invalid syntax for +0.0e+NaN on platforms
that lack NaNs.
(string_to_number): On non-IEEE platforms, return HUGE_VAL
for infinity and a string for NaN.  All callers changed.