57 lines
1.6 KiB
Plaintext
57 lines
1.6 KiB
Plaintext
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SOME NOTES ON FACTOR'S FFI
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The FFI is quite a neat design and I think it is better than JNI and
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similar approaches. Also, it offers better performance than libffi et
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al. Of course, both of those technologies are great and Factor FFI has
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its drawbacks -- namely, its not portable.
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All FFI words are in the "alien" vocabulary.
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The basic principle is generating machine stubs from C function
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prototypes. The main entry point is the 'alien-call' word, which is
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defined as simply throwing an error. However, it is given special
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compilation behavior. This means it can only be used in compiled words.
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Here is an example from sdl-video.factor:
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: SDL_LockSurface ( surface -- )
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"int" "sdl" "SDL_LockSurface" [ "surface*" ] alien-call ; compiled
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The parameters are:
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"int" - return type. later it will be surface*
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"sdl" - library
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"SDL_LockSurface" - function
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[ "surface*" ] - parameters
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Note the word ends with 'compiled'. This is a hack and won't be needed
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later.
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Parameters and return values are C type names. C types include the
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following:
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- char - 1 byte signed
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- short - 2 bytes signed
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- int - 4 bytes signed
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- void* - word-size width field, can only be used as a parameter
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Structs can be defined in this fashion:
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BEGIN-STRUCT: point
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FIELD: int x
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FIELD: int y
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END-STRUCT
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And then referred to in parameter type specifiers as "point*". Struct
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return values are not yet supported.
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Enumerations can be defined; they simply become words that push
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integers:
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BEGIN-ENUM: 0
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ENUM: int xuzzy
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ENUM: int bax
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END-ENUM
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The parameter to BEGIN-ENUM specifies the starting index.
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