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FFI: Simplify initializer rules. Clarify docs.

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This commit is contained in:
Mike Pall
2011-01-23 14:23:21 +01:00
parent f529d22869
commit 72b3fff72f
6 changed files with 58 additions and 33 deletions
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11
doc/ext_ffi.html
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@@ -73,8 +73,8 @@ The FFI library is tightly integrated into LuaJIT (it's not available
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.
@@ -253,14 +253,17 @@ would consume 40&nbsp;Megabytes in plain Lua (on x64).
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&nbsp;functions, especially I/O functions,