* Strings with 0xFF byte prefix are considered special symbols: they have
typeof "symbol" but still mostly behave as strings (e.g. allow ToString)
so that existing code dealing with internal keys, especially inside
Duktape, can work with fewer changes.
* Strings with 0x80 byte prefix are global symbols, e.g. Symbol.for('foo')
creates the byte representatio: 0x80 "foo"
* Strings with 0x81 byte prefix are unique symbols; the 0x81 byte is followed
by the Symbol description, and an internal string component ensuring
uniqueness is separated by a 0xFF byte (which can never appear anywhere in
an extended UTF-8 string). The unique suffix is up to Duktape internals,
currently two 32-bit counters are used. For example:
0x81 "mySymbol" 0xFF "0-17".
* Well-known symbols use the 0x81 prefix but lack a unique suffix, so their
format is 0x81 <description> 0xFF.
* ES6 distinguishes between an undefined symbol description and an empty
string symbol description. This distinction is not currently visible via
Ecmascript bindings but may be visible in the future. Append an extra
0xFF to the unique suffix when the description is undefined, i.e.
0x81 0xFF <unique suffix> 0xFF.
These can be used whenever we're 100% certain that the value stack index
exists and the type matches expected type. When these are true, a
duk_hstring, duk_hbuffer, or duk_hobject pointer fetch can be inlined to
small code.
Saves a few hundred bytes of footprint:
* duk_dup_0() = duk_dup(ctx, 0), duk_dup_1() = duk_dup(ctx, 1), etc.
* duk_dup_m2() = duk_dup(ctx, -2), etc.
* duk_dup_m1() is not added, because duk_dup_top() is the same thing
* Plain buffers still inherit from ArrayBuffer.prototype.
* Plain buffers won't object coerce, so Object(plainBuffer) fails.
* All buffer object related methods throw an error; their function bodies
are essentially empty. Note that this includes bindings such as
String.fromBuffer(), ArrayBuffer.allocPlain(), ArrayBuffer.plainOf(),
and so on. In essence, you can index plain buffers in Ecmascript but
the buffer values must be created via the C API.
* Duktape custom bindings like Duktape.dec('hex', 'deadbeef') still work
and produce plain buffers.
* Remove CSPROP(I) opcode. CSPROP usually leads to three opcodes, e.g.
LDREG + LDCONST + CSPROP. Direct loads for 'base[key]' and 'base' has
the same effect with one opcode shorter bytecode and no need for a
separate CSPROP opcode.
* Remove CSREGI (indirect) opcode, simplify CSREG opcode a bit. Extend
CSREG base register argument to be wider (BC) so that shuffling is not
needed in practice.
* Remove CSVARI (indirect) opcode and handle its equivalent by using explicit
shuffling in the compiler. This removes one opcode, and indirect target
check from CSVAR.
* Remove NEWI and extend base register argument of NEW to be wider (BC) so
that shuffling is not needed in practice.
* Remove CALLI, and split CALL into CALL, TAILCALL, and EVALCALL. This
eliminates the flags field (A) and allows the base register to be wider
(BC), eliminating the need for shuffling in practice.
* Maximum argument count to constructor and ordinary calls drops from 511
to 255 with this change.
Change handling of plain buffers so that they behave like ArrayBuffer
instances to Ecmascript code, with limitations such as not being
extensible and all properties being virtualized. This simplifies
Ecmascript code as plain buffers are just lightweight ArrayBuffers
(similarly to how lightfuncs appear as function objects). There are
a lot of small changes in how the built-in objects and methods, and
the C API deals with plain buffer values.
Also make a few small changes to plain pointer and lightfunc handling
to improve consistency with how plain buffers are now handled.
These don't play well with the API currently: the Duktape specific error
codes don't have Ecmascript Error class counterparts so they don't get
represented usefully as Ecmascript objects (e.g. AllocError is a plain
Error from Ecmascript point of view).
There's no real need for Duktape specific error code. Some of the codes
had become unused; a couple were used but Ecmascript standard types can
be used instead.
Also minor error message tweaking.
Improve readability by doing the following renames:
* duk_hcompiledfunction -> duk_hcompfunc
* duk_hnativefunction -> duk_hnatfunc
* duk_hbufferobject -> duk_hbufobj
Corresponding renames for all caps defines.
Scanbuild fixes:
* duk_cmdline.c realloc() failure could leak memory, fixed.
* Other fixed scanbuild errors were harmless.
* Remaining errors are invalid memory access in panic (intentional
segfault) and a Date handling case where garbage data is intentionally
assigned as doing so is harmless and intended.
Avoid unnecessary index re-check in num coercion.
* Use shared error macros and shared error handler to reduce the size of call
sites of common errors.
* Make zero argument DUK_ERROR() calls non-vararg calls to reduce call site
footprint. Non-vararg calls have smaller call sites and because there are
a lot of call sites, this turns out to be significant.
* Remove variadic macros from internal DUK_ERROR() macro set and add separate
macros for argument counts 0 to 4; this is more portable and requires less
conditional code, and works well when a non-vararg call is used for most
error call sites.
* Rework macro / function argument order for the error path, try to keep 'thr'
in the same argument slot to avoid unnecessary register moves.
* Pack linenumber and error code into a single 32-bit argument when possible,
removes one more constant load from the call site.
* Convert some internal errors to RangeErrors when the underlying cause is an
implementation limit (such as a compiler temp limit) rather than an actual
unexpected internal situation.
* Simplify and share a few error messages to reduce string count.
Accept a plain buffer argument in typedarray constructor. Behavior will be
the same as for a Duktape.Buffer, i.e. the argument is treated as an array-like
initializer.
Zero buffer data explicitly for ArrayBuffer and typedarrays created, even when
DUK_USE_ZERO_BUFFER_DATA option is not set. Buffer zeroing is explicitly
required by Khronos/ES6.
Node.js Buffer does *not* zero buffer data by default, so this behavior
is not changed here: Node.js Buffers will be zeroed when
DUK_USE_ZERO_BUFFER_DATA is set, and left as garbage when not set.
The check for "source ends before destination" was off by one, causing a
corner case no-overlap case to be treated like a have-overlap case. This
is harmless but makes the copy slower than necessary.
Add a C API binding for Object.defineProperty(): duk_def_prop().
In addition to Object.defineProperty() features, the API call provides a
"force" flag which allows properties to be added to non-extensible objects
and non-configurable properties to be changed (except virtual properties
which are immutable).
Because the name duk_def_prop() conflicts with internal calls, rename them
from duk_def_prop*() to duk_xdef_prop*(). This rename also makes it clearer
that the internal duk_xdef_prop*() calls have non-compliant, internal
semantics.
Also reimplement Object.defineProperty() and Object.defineProperties() (and
duk_def_prop()) so that they share the same internal helpers, and there is
no need for a temporary property descriptor object which is unnecessary churn.
Detailed changes:
- New helper to prepare (validate and normalize) property descriptors
- New helper to implement Object.defineProperty() internals, leaving
out validation of the property descriptor
- Reimplement Object.defineProperty() using the new helpers
- Reimplement Object.defineProperties() using the new helpers
- Reimplement duk_define_property() using the new helpers, so that a
temporary property descriptor object is no longer created
- Add support for "force" flag to Object.defineProperty()
* Fix outstanding FIXME issues for lightfunc semantics.
* Improve API and Ecmascript testcases to match.
* Clarify lightfunc limitations, e.g. finalizer limitations.
* Guide and API documentation changes for lightfuncs.
* Fix compile warning: duk_str_not_object unused.
Sami Vaarala