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57 lines
2.1 KiB
57 lines
2.1 KiB
Writing a table generator |
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This documentation is preliminary. |
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Parts of the API are not good and should be changed. |
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Basic concepts |
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A table generator consists of two files, *_tablegen.c and *_tablegen.h. |
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The .h file will provide the variable declarations and initialization |
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code for the tables, the .c describes the tables so they can be printed |
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as a header file. |
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Both of these files will be compiled for the host system, so to avoid |
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breakage with cross-compilation neither of them may include, directly |
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or indirectly, config.h or avconfig.h. |
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Due to this, the .c file or Makefile may have to provide additional defines |
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or stubs, though if possible this should be avoided. |
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The .c file |
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This file should include the *_tablegen.h and tableprint.h files and |
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anything else it needs as long as it does not depend on config.h or |
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avconfig.h. |
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In addition to that it must contain a void tableinit(void) function |
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which initializes all tables by calling the init functions from the .h |
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file. |
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It must also contain a "const struct tabledef tables[]" array describing |
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the tables to be generated. |
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Its entries consist of (in order): |
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- a string suitable for declaring the table, up to but not including the = |
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NULL terminates the table |
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- a function to print the table - tableprint.h defines some defaults, |
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e.g. write_uint8_array to print a uint8_t array. |
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- a pointer to the table |
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- the size of the first dimension of the array |
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- if applicable, the size of the second dimension of the array |
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The .h file |
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This file should contain: |
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- one or more initialization functions |
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- the table variable declarations |
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If CONFIG_HARDCODED_TABLES is set, the initialization functions should |
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not do anything, and instead of the variable declarations the |
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generated *_tables.h file should be included. |
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Since that will be generated in the build directory, the path must be |
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included, i.e. |
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#include "libavcodec/example_tables.h" |
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not |
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#include "example_tables.h" |
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Makefile changes |
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To make the automatic table creation work, you must manually declare the |
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new dependency. |
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For this add a line similar to this: |
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$(SUBDIR)example.o: $(SUBDIR)example_tables.h |
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under the "ifdef CONFIG_HARDCODED_TABLES" section in the Makefile.
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