The growth rate of string buffers was reduced from 2 to 1.5 (3/2).
As string buffers start larger (256~1024 bytes), they don't need to
grow that fast. Moreover, a lower rate allows multiplicative growth up
to larger sizes (3/2 of the maximum). (After that, the growth becomes
linear, which is mostly useless.)
'luaD_growstack' already checks that. This commit also fixes an
internal bug in 'luaD_growstack': a large 'n' could cause an arithmetic
overflow when computing 'needed'.
The use of 'l_likely' in auxlib macros 'luaL_argcheck' and
'luaL_argexpected' should not be restricted to Lua's own code.
For that, 'l_likely' was renamed to 'luai_likely' to be exported
to external code.
More uses of macros 'likely'/'unlikely' (renamed to
'l_likely'/'l_unlikely'), both in range (extended to the
libraries) and in scope (extended to hooks, stack growth).
'luaconf.h' always defines options LUA_32BITS, LUA_C89_NUMBERS,
LUA_INT_TYPE, and LUA_FLOAT_TYPE (using 0/1 for the first two),
to avoid they being set through compiler options. (It is too easy
to forget these options when compiling other software that
interoperates with Lua.)
A "with stack" implementation gains too little in performance to be
worth all the noise from C-stack overflows.
This commit is almost a sketch, to test performance. There are several
pending stuff:
- review control of C-stack overflow and error messages;
- what to do with setcstacklimit;
- review comments;
- review unroll of Lua calls.
- Better documentation in 'testes/cstack.lua' about using
'debug.setCstacklimit' to find a good limit.
- Constant LUAI_MAXCSTACK gets added CSTACKERR (extra stack for
error handling), so that it is compatible with the argument to
'debug.setCstacklimit'.
- new error message for "attempt to assign to const variable"
- note in the manual about compatibility options
- comments
- small changes in 'read_line' and 'pushstr'
- The preprocessor must work with at least 'long', and therefore must
do shifts of up to 31 bits correctly.
- Whenever possible, use unsigned types in shifts.
- 'L' added to the 'BuffFS' structure
- '%c' does not handle control characters (it is not its business.
This now is done by the lexer, who is the one in charge of that
kind of errors.)
- avoid the direct use of 'l_sprintf' in the Lua kernel
The function 'luaO_pushvfstring' now uses an internal buffer to
concatenate small strings, instead of pushing all pieces on the
stack. This avoids the creation of several small Lua strings for each
piece of the result. (For instance, a format like "n: '%d'" used to
create three intermediate strings: "n: '", the numeral, and "'".
Now it creates none.)
The result of "string.format("%.99f", -1e308) is 410 characters long,
but all other formats have much smaller limits (at most 99 plus a fex
extras). This commit avoids 'string.format' asking for a buffer
~400 chars large when ~100 will do.
The limit LUAI_MAXCCALLS was renamed LUAI_MAXCSTACK, which better
represents its meaning. Moreover, its definition was moved to
'luaconf.h', given its importance now that Lua does not use
a "stackless" implementation.
* unification of the 'nny' and 'nCcalls' counters;
* external C functions ('lua_CFunction') count more "slots" in
the C stack (to allow for their possible use of buffers)
* added a new test script specific for C-stack overflows. (Most
of those tests were already present, but concentrating them
in a single script easies the task of checking whether
'LUAI_MAXCCALLS' is adequate in a system.)
The visibility for functions marked as LUAI_FUNC was changed from
"hidden" to "internal". These functions cannot be called from
outside the Lua kernel, and "internal" visibility offers more
chances for optimizations.
As hinted in the manual for Lua 5.3, the emulation of the metamethod
for '__le' using '__le' has been deprecated. It is slow, complicates
the logic, and it is easy to avoid this emulation by defining a proper
'__le' function.
Moreover, often this emulation was used wrongly, with a programmer
assuming that an order is total when it is not (e.g., NaN in
floating-point numbers).
