The align trick used in duk_hbuffer_fixed uses a union which includes an
IEEE double for align-by-8. Also include a duk_uint64_t if available in
case double/integer align requirements differ.
The cast from duk_hbuffer to duk_hbuffer_fixed seemingly increases alignment
requirement from 4 to 8 because duk_hbuffer_fixed is forced to pack to 8 bytes
(so that data following the buffer is properly aligned). However, because the
struct base pointer is always aligned by 8 when the platform requires alignment
by 8, the warning is harmless and can be avoided by casting through a void *.
An external buffer is similar to a dynamic buffer but the external data
pointer is managed by user code rather than Duktape, and may point to an
arbitrary address. For example, user can build an external buffer which
points to a framebuffer and operate on that framebuffer from Ecmascript
code via the buffer.
- Disable JSON.stringify() fastpath by default
- Rework to use DUK_USE_ALIGN_BY config option
- Replace previous DUK_USE_ALIGN_4 and DUK_USE_ALIGN_8 with a cleaner
DUK_USE_ALIGN_BY config option (allowed values 1, 4, 8)
- Add fastpath tag in anticipation of automatic fastpath suggestions
or warnings
Also remove mostly unused old debug code.
Debug code doesn't have access to 'heap' so it cannot decode pointers.
Cause an #error for now if both debug prints and pointer compression
are enabled at the same time.
Remove duk_debug_hobject.c from make and dist. It was out of date and
not used in practice anymore.
Memory optimization work for very low memory devices (96 to 256kB system RAM).
Overall changes are:
- 16-bit fields for various internal structures to reduce their size
- Heap pointer compression to reduce pointer size to 16 bits
When DUK_OPT_LIGHTFUNC_BUILTINS and the new low memory options are enabled,
Duktape initial heap memory usage is about 23kB (compared to baseline of
about 45kB) on x86.
Unless low memory feature options are enabled, there should be no visible
changes to Duktape behavior.
More detailed changes:
- 16-bit changes for duk_heaphdr: pointer compression, refcount
- 16-bit changes for duk_hstring: hash, blen, and clen can all be 16 bits,
use 0xFFFF as string byte length limit (call sites ensure this limit is
never exceeded)
- 16-bit changes for duk_hbuffer, use 0xFFFF as buffer length limit
- 16-bit fields for hobject size (entry part, array part), drop hash part
since it's not usually needed for extremely low memory environments
- 16-bit changes for duk_hcompiledfunction
- Heap pointer packing for stringtable
- Heap pointer packing for 'strs' built-in strings list (saves around 600
to 700 bytes but may not be a good tradeoff because call site size will
increase)
Other changes:
- Heaphdr NULL init fix. The original macros were broken: the double/single
linked macro variants were the wrong way around. Now sets through macro
to work properly with compressed pointers.
- Rename duk_hbuffer CURR_DATA_PTR -> DATA_PTR to reduce macro length
(previous name was tediously long)
- Rename buffer "usable_size" to "alloc_size" throughout as they have been
the same for a while now (they used to differ when buffer had an extra NUL).
- Add memory optimization markers to Duktape.env (pointer compression and
individual 16-bit field options)
- Rename a few internal fields for clarity: duk_hobject 'p' to 'props',
heap->st to heap->strtable
- Add a safety check for buffer alloc size (should not be triggered but
prevents wrapping if call sites don't properly check for sizes)
- Other minor cleanups
These were revealed after fixing DUK_SINGLE_FILE, gcc will complain about
these internal functions being declared, defined, but not used. There were
also a few declared functions that did not exist. Compiled binary size was
reduced by a few kilobytes!
Unused functions must be commented out carefully: some functions might be
used with certain feature options but not by the defaults. These removals
were verified with grep.
There are no call sites for DUK_DEBUG_DUMP_HEAP() so all the functions
in duk_debug_heap.c are unused, even with a debug build.
Out of the checked allocation macros, only DUK_REALLOC_INDIRECT_CHECKED() is
actually in use at the moment. This commit just comments the unused stuff
out, but it might be better to just remove the unused stuff entirely.
Sami Vaarala