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Configuration
-------------
Natural ratio between input and output: n:m
Unseekable <=== (n == 0 || m == 0)
Configurational state
---------------------
Chosen ratio, without user intervention
Flag, possible to overide ratio above or not ?
Chosen ratio, after possible intervention by user
State
-----
Stream location of transformation. UpLoc
Stream location of start and end of the read buffer. UpLocBS, UpLocBE
Stream location of downstream channel. DwLoc
"End" = Location of the character behind the last character in the buffer.
!Integrity condition: (1) DwLoc "equivalent to" UpLocBE
(2) UpLocBS = UpLocBE = UpLoc for an empty buffer.
(3) UpLoc* % n == 0, i.e. a multiple of n.
Derived state
-------------
(up * m) / n = down (Position relative to starting point)
Zero = Position downstream "equivalent to" Zero position upward.
(1) DwLoc "equivalent to" UpLocBE
===> (UpLocBE * m) / n + Zero = DwLoc
===> Zero = (UpLocBE * m) / n - DwLoc
Actions
-------
Tell /done/
....
Report stream location of transformation.
Seek, general /done/
.............
[Tell]
Unseekable
===> Error
STOP_____________________________
Identity
===> discard read/write buffers,
pass request
set flag "changed"
STOP_____________________________
Seek, relative to start of stream (as seen by the transformation) /done/
.................................................................
Delta = NewPos - UpLoc
Seek (Delta, relative to current position)
STOP_____________________________
Seek, relative to current position (as seen by the transformation) /done/
..................................................................
(Delta % n) != 0
===> Error
NewUpLoc := UpLoc + Delta
NewUpLoc < 0
===> Error
NewUpLoc < UpLocBS
|| NewUpLoc >= UpLocBE
===> Discard read buffer
DeltaDown := ((NewUpLoc - UpLocBE) * m) / n
DeltaDown != 0
===> Seek down, relative to current: DeltaDown.
DwLoc := DwLoc + DeltaDown
UpLoc,UpLocBS,UpLocBE := NewUpLoc
STOP_____________________________
UpLoc := NewUpLoc
STOP_____________________________
Seek, relative to end of stream
...............................
??? not yet
STOP_____________________________
Write /done/
.....
// Partial writes (incomplete tuple?, seek effect)
// no seek!, no change of location
// next read discards incomplete information.
// next seek discards incomplete information! too.
UpLoc != UpLocBE
===> Get Zero
Discard read buffer.
DeltaDown := ((UpLocBE - UpLoc) * m) / n
Seek down, relative: DeltaDown.
DwLoc := DwLoc + DeltaDown
-- Now UpLoc "equivalent to" DwLoc
-- IOW Positions up and down are now in sync.
-- Phase == 0 now!
UpLoc,UpLocBS,UpLocBE := UpLoc += toWrite
DwLoc += (toWrite * m)/n
Write complete transformation results.
STOP_____________________________
// Handle only complete writes, in writer proc, do the above.
// Automatic handling of incomplete tuples as described //above
UpLoc == UpLocBE
-- No read buffer existing, positions are in sync.
Write complete transformation results.
STOP_____________________________
Read
....
Discard incomplete tuples in write buffer!
Repeat
Data in read buffer
===> Copy x from read buffer
UpLoc += x
Remove x from buffer
LOOP
Satisified
===> STOP
(Integrity: UpLoc == UpLocBE)
got := Read from down
transform
// got % m == 0 not assertable, can be fract
// maintain phase! value as last ditch correction value
DwLoc += got
UpLocBS := UpLocBE
UpLocBE += (got-phase) / m * n
endrepeat
STOP_____________________________
Stack /done/
.....
UpLoc,UpLocBS,UpLocBE := 0
DwLoc := Tell down.
Phase == 0.
Empty read/write buffers.
STOP_____________________________
Force identity
..............
Set flag "identity"
Unset flag "changed"
STOP_____________________________
Unforce identity
................
Changed
===> See "Stack"
STOP_____________________________
...
handling force unseekable ? for seekable transforms.
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