Feature #1493
[patch] lex_state as bit field / IS_lex_state() macro
| Status: | Assigned | Start date: | 05/20/2009 | |
|---|---|---|---|---|
| Priority: | Low | Due date: | ||
| Assignee: |  nobu (Nobuyoshi Nakada) |
% Done: | 0% |
|
| Category: | core | |||
| Target version: | 2.0.0 |
Description
# ? Changelog:
# Represent lex_state by bit field instead of serial integer enum
# so that single or multiple values can be checked together using
# unifying macro IS_lex_state(). States remain mutually exclusive.
Example:
Each use of current macro IS_BEG() ..
#define IS_BEG() (lex_state == EXPR_BEG || lex_state == EXPR_MID || \
lex_state == EXPR_VALUE || lex_state == EXPR_CLASS)
.. results in up to 4 tests which can be reduced to 1.
An extreme use case ..
if (IS_BEG() ||
lex_state == EXPR_DOT ||
IS_ARG()) {
.. requires up to 7 tests on lex_state.
To my knowledge, compilers can't optimize this.
As a bit field, there's no need to:
if (IS_lex_state( EXPR_BEG_ANY | EXPR_ARG_ANY | EXPR_DOT ))
.. reduces to: if (lex_state & (test_bits)) // TRUE/FALSE
All changes in this patch were scripted to eliminate the possibility
of typos. Where some replaced sections looked similar or the same,
they were verified with MD5sum before applying!
Multiple state tests were merged using simple, strict logic and any
"surprise" code would have been left unchanged.
Therefore, it should not be necessary to check every line of the patch;
I hope that a check of a random sample will give confidence in the rest.
There were several repeated switches which could have been replaced with:
lex_state = (IS_lex_state( EXPR_FNAME | EXPR_DOT )) ? EXPR_ARG : EXPR_BEG
but I assumed you would prefer if-else for flexibility and legibility:
if (IS_lex_state( EXPR_FNAME | EXPR_DOT )) {
lex_state = EXPR_ARG;
}
else {
lex_state = EXPR_BEG;
}
Say what you don't like about anything - it might be easy to change. :)
Wouldn't it be nice to use some spare bits to combine other state?
if ((lex_state == EXPR_BEG && !cmd_state) || ...
if (IS_ARG() && space_seen && ...
- I haven't explored those, yet.
My motivation was not to reduce processor heat. ;)
In the future, if we need to break the dependence on Yacc/Bison, these
state transitions might need to become token information and the change
makes them far easier to store.
( e.g. Any of 'THESE states' => 'THIS state' )
daz
History
Updated by marcandre (Marc-Andre Lafortune) over 2 years ago
- Category set to core
- Assignee set to matz (Yukihiro Matsumoto)
- Priority changed from Normal to Low
Updated by znz (Kazuhiro NISHIYAMA) about 2 years ago
- Category set to core
- Status changed from Open to Assigned
- Target version set to 2.0.0
Updated by mame (Yusuke Endoh) 3 months ago
- Assignee changed from matz (Yukihiro Matsumoto) to nobu (Nobuyoshi Nakada)
Nobu, aren't you interested in this? Could you please review and
import the patch if it looks good to you?
This seems to be just a patch for refactoring. Though, the purpose
is not so clear to me. (Who is planning to break the dependence on
bison?) But, the patch seems benign (I read only the ticket, not
the patch itself).
--
Yusuke Endoh <mame@tsg.ne.jp>