as a separate module). The code generated by the JIT-compiler for
accesses to C data structures from Lua code is on par with the
code a C compiler would generate. Calls to C functions can
-be inlined in the JIT-compiled code, unlike calls to functions bound
-via the classic Lua/C API.
+be inlined in JIT-compiled code, unlike calls to functions bound via
+the classic Lua/C API.
</p>
<p>
This page gives a short introduction to the usage of the FFI library.
Next, performance: the pure Lua version runs in 9.57 seconds (52.9
seconds with the Lua interpreter) and the FFI version runs in 0.48
seconds on my machine (YMMV). That's a factor of 20x faster (110x
-faster than with plain Lua).
+faster than the Lua interpreter).
</p>
<p style="font-size: 8pt;">
The avid reader may notice that converting the pure Lua version over
to use array indexes for the colors (<tt>[1]</tt> instead of
<tt>.red</tt>, <tt>[2]</tt> instead of <tt>.green</tt> etc.) ought to
be more compact and faster. This is certainly true (by a factor of
-~1.7x), but the resulting code would be less idiomatic and rather
+~1.7x). Switching to a struct-of-arrays would help, too.
+</p>
+<p style="font-size: 8pt;">
+However the resulting code would be less idiomatic and rather
error-prone. And it still doesn't get even close to the performance of
the FFI version of the code. Also, high-level data structures cannot
be easily passed to other C functions, especially I/O functions,
a constructor and is otherwise fully equivalent.
</p>
<p>
-The <tt>init</tt> arguments provide optional initializers. The created
-cdata object is filled with zero bytes if no initializers are given.
-Scalar types accept a single initializer. Aggregates can either be
-initialized with a flat list of initializers or a single aggregate
-initializer (see the <a href="ext_ffi_semantics.html#convert">C type
-conversion rules</a>). Excess initializers cause an error.
-</p>
-<p>
-If a single initializer is given for an array, it's repeated for all
-remaining elements. This doesn't happen if two or more initializers
-are given — all uninitialized elements are filled with zero
-bytes. The fields of a <tt>struct</tt> are initialized in the order of
-their declaration. Uninitialized fields are filled with zero bytes.
-Only the first field of <tt>union</tt> can be initialized with a flat
-initializer. Elements or fields which are aggregates themselves are
-initialized with a <em>single</em> <tt>init</tt> argument, but this
-may be an aggregate initializer of course.
+The cdata object is initialized according to the
+<a href="ext_ffi_semantics.html#init">rules for initializers</a>,
+using the optional <tt>init</tt> arguments. Excess initializers cause
+an error.
</p>
<p>
Performance notice: if you want to create many objects of one kind,
<h3 id="ffi_abi"><tt>status = ffi.abi(param)</tt></h3>
<p>
Returns <tt>true</tt> if <tt>param</tt> (a Lua string) applies for the
-target ABI (Application Binary Interface). Otherwise returns
-<tt>false</tt>. The following parameters are currently defined:
+target ABI (Application Binary Interface). Returns <tt>false</tt>
+otherwise. The following parameters are currently defined:
</p>
<table class="abitable">
<tr class="abihead">
TODO
</p>
+<h2 id="init">Initializers</h2>
+<p>
+Creating a cdata object with <a href="ffi_ext_api.html#ffi_new">ffi.new()</a>
+or the equivalent constructor syntax always initializes its contents,
+too. Different rules apply, depending on the number of optional
+initializers and the C types involved:
+</p>
+<ul>
+<li>If no initializers are given, the object is filled with zero bytes.</li>
+
+<li>Scalar types (numbers and pointers) accept a single initializer.
+The standard <a href="#convert">C type conversion rules</a>
+apply.</li>
+
+<li>Valarrays (complex numbers and vectors) are treated like scalars
+when a single initializer is given. Otherwise they are treated like
+regular arrays.</li>
+
+<li>Aggregate types (arrays and structs) accept either a single
+compound initializer (Lua table or string) or a flat list of
+initializers.</li>
+
+<li>The elements of an array are initialized, starting at index zero.
+If a single initializer is given for an array, it's repeated for all
+remaining elements. This doesn't happen if two or more initializers
+are given: all remaining uninitialized elements are filled with zero
+bytes.</li>
+
+<li>The fields of a <tt>struct</tt> are initialized in the order of
+their declaration. Uninitialized fields are filled with zero
+bytes.</li>
+
+<li>Only the first field of a <tt>union</tt> can be initialized with a
+flat initializer.</li>
+
+<li>Elements or fields which are aggregates themselves are initialized
+with a <em>single</em> initializer, but this may be a compound
+initializer or a compatible aggregate, of course.</li>
+
+</ul>
+
<h2 id="clib">C Library Namespaces</h2>
<p>
A C library namespace is a special kind of object which allows
** This is true if an aggregate is to be initialized with a value.
** Valarrays are treated as values here so ct_tv handles (V|C, I|F).
*/
-int lj_cconv_multi_init(CTState *cts, CType *d, TValue *o)
+int lj_cconv_multi_init(CType *d, TValue *o)
{
if (!(ctype_isrefarray(d->info) || ctype_isstruct(d->info)))
return 0; /* Destination is not an aggregate. */
if (tvistab(o) || (tvisstr(o) && !ctype_isstruct(d->info)))
return 0; /* Initializer is not a value. */
- if (tviscdata(o)) {
- CTInfo info = lj_ctype_rawref(cts, cdataV(o)->typeid)->info;
- if (ctype_isrefarray(info) || ctype_isstruct(info))
- return 0; /* Initializer is not a value. */
- }
return 1; /* Otherwise the initializer is a value. */
}
{
if (len == 0)
memset(dp, 0, sz);
- else if (len == 1 && !lj_cconv_multi_init(cts, d, o))
+ else if (len == 1 && !lj_cconv_multi_init(d, o))
lj_cconv_ct_tv(cts, d, dp, o, 0);
else if (ctype_isarray(d->info)) /* Also handles valarray init with len>1. */
cconv_array_init(cts, d, sz, dp, o, len);
LJ_FUNC void lj_cconv_ct_tv(CTState *cts, CType *d,
uint8_t *dp, TValue *o, CTInfo flags);
LJ_FUNC void lj_cconv_bf_tv(CTState *cts, CType *d, uint8_t *dp, TValue *o);
-LJ_FUNC int lj_cconv_multi_init(CTState *cts, CType *d, TValue *o);
+LJ_FUNC int lj_cconv_multi_init(CType *d, TValue *o);
LJ_FUNC void lj_cconv_ct_init(CTState *cts, CType *d, CTSize sz,
uint8_t *dp, TValue *o, MSize len);
CType *d = ctype_raw(cts, id);
TRef trcd = emitir(IRTG(IR_CNEW, IRT_CDATA), trid, TREF_NIL);
J->base[0] = trcd;
- if (J->base[1] && !J->base[2] &&
- !lj_cconv_multi_init(cts, d, &rd->argv[1])) {
+ if (J->base[1] && !J->base[2] && !lj_cconv_multi_init(d, &rd->argv[1])) {
goto single_init;
} else if (ctype_isarray(d->info)) {
CType *dc = ctype_rawchild(cts, d); /* Array element type. */
projects / thirdparty / LuaJIT.git / commitdiff
