85 lines
4.2 KiB
ArmAsm
85 lines
4.2 KiB
ArmAsm
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;****************************************************************************
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;* SET-FILE-POSITION will move the file pointer to a new position *
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;* and update a pointer in the buffer to point to a new location. *
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;* The offset variable can be: *
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;* 0 for positioning from the start of the file *
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;* 1 for positioning relative to the current position *
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;* 2 for positioning from the end of the file *
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;****************************************************************************
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(define set-file-position! ; ==> filepos.s
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(lambda (port #-of-bytes offset)
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(let ((current-pos (%reify-port port 9))
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(end-of-buffer (%reify-port port 10))
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(new-pos '())
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(current-chunk (max 0 (-1+ (%reify-port port 12))))
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(new-chunk '())
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(messages '())
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(file-size (+ (* (%reify-port port 4) 65536) (%reify-port port 6)))
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(port-flags (%reify-port port 11)))
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(if (and (port? port)
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(=? (%logand port-flags 4) 0))
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(case offset
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((0) ; offset from the start of the file
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(set! #-of-bytes (abs #-of-bytes))
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(if (=? (%logand port-flags 3) 0)
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(set! #-of-bytes (min #-of-bytes file-size)))
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(set! new-chunk (truncate (/ #-of-bytes 256)))
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(set! new-pos (- #-of-bytes (* new-chunk 256)))
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(if (and (<? new-pos end-of-buffer)
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(>=? new-pos 0)
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(=? (%logand port-flags 3) 0) ; open for reading
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(=? new-chunk current-chunk))
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(%reify-port! port 9 new-pos)
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(%sfpos port new-chunk new-pos)))
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((1) ; offset from the current position
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(set! new-pos (+ current-pos #-of-bytes))
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(if (and (<? new-pos end-of-buffer)
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(>=? new-pos 0)
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(=? (%logand port-flags 3) 0)) ; open for reading
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(%reify-port! port 9 new-pos)
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(begin
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(set! new-pos (+ (+ current-pos (* 256 current-chunk))
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#-of-bytes)) ; offset from the begining of the file
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(if (and (>? new-pos file-size)
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(=? (%logand port-flags 3) 0))
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(set! new-pos file-size))
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(if (<? new-pos 0)
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(set! new-pos 0))
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(set! new-chunk (truncate (/ new-pos 256)))
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(%sfpos port new-chunk (- new-pos (* new-chunk 256))))))
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((2) ; offset from the end of the file
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(set! #-of-bytes (min (abs #-of-bytes) file-size))
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(set! new-pos (- file-size (abs #-of-bytes))) ; absolute position
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(set! new-chunk (truncate (/ new-pos 256)))
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(set! new-pos (- newpos (* new-chunk 256))) ; buffer position
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(if (=? (%logand port-flags 3) 0)
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(if (and (<? new-pos end-of-buffer)
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(>=? new-pos 0)
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(=? new-chunk current-chunk))
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(%reify-port! port 9 new-pos)
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(%sfpos port new-chunk new-pos))
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(display "Offset from the end of the file can only be used with files open for reading!")
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))
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(else (display "Offset must be 0, 1 or 2!")))
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(display "First parameter must be a file!")))))
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;******************************************************************
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;* get-file-position will return the current file position in the *
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;* number of bytes from the beginning of the file. *
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;******************************************************************
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(define get-file-position
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(lambda (port)
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(let (( result '())
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(chunk (max 1 (%reify-port port 12))))
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(if (and (port? port)
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(=? (%logand (%reify-port port 11) 4) 0))
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(set! result (+ (* 256 (-1+ chunk)) ; chunk#
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(%reify-port port 9))) ; current position
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(set! result "Needs to be a port/file object!"))
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result)))
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