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Diffstat (limited to 'filter/f-inst.h')
| -rw-r--r-- | filter/f-inst.h | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/filter/f-inst.h b/filter/f-inst.h index 4b42c57c..1e2d63a2 100644 --- a/filter/f-inst.h +++ b/filter/f-inst.h @@ -5,6 +5,41 @@ * (c) 2018--2019 Maria Matejka <mq@jmq.cz> * * Can be freely distributed and used under the terms of the GNU GPL. + * + * Filter interpreter data structures and internal API. + * The filter code goes through several phases: + * + * 1 Parsing + * Flex- and Bison-generated parser decodes the human-readable data into + * a struct f_inst tree. This is an infix tree that was interpreted by + * depth-first search execution in previous versions of the interpreter. + * All instructions have their constructor: f_new_inst(FI_code, ...) + * translates into f_new_inst_FI_code(...) and the types are checked in + * compile time. + * + * 2 Postfixify before interpreting + * The infix tree is always interpreted in the same order. Therefore we + * sort the instructions one after another into struct f_line. Results + * and arguments of these instructions are implicitly put on a value + * stack; e.g. the + operation just takes two arguments from the value + * stack and puts the result on there. + * + * 3 Interpret + * The given line is put on a custom execution stack. If needed (FI_CALL, + * FI_SWITCH, FI_AND, FI_OR, FI_CONDITION, ...), another line is put on top + * of the stack; when that line finishes, the execution continues on the + * older lines on the stack where it stopped before. + * + * 4 Same + * On config reload, the filters have to be compared whether channel + * reload is needed or not. The comparison is done by comparing the + * struct f_line's recursively. + * + * The main purpose of this rework was to improve filter performance + * by making the interpreter non-recursive. + * + * The other outcome is concentration of instruction definitions to + * one place -- filter/f-inst.c */ #ifndef _BIRD_F_INST_H_ |