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OVERLAY stage v1.0 |
Pipelines v1.6 |
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Purpose, Operands, Streams used, Usage notes, Examples, See also |
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Syntax |
_SPACE_
>>__OVERlay__|_______|_________________________________________________________________><
|_char__|
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Purpose |
Use the OVERLAY stage to read one record from each connected input stream and create a single output record such that each position in the output record contains the character in the relative position from the highest-numbered input stream. OVERLAY writes the output record to its primary output stream.
One character has the property that it does not overlay a character from a lower-numbered stream. By default, this character is a space. The operand may select a different character. If a record in the highest-numbered input stream contains the specified character in any position, OVERLAY replaces the character in the output record with the corresponding character from the next highest-numbered input stream that has something other than the specified character in that position.
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Operands |
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● |
SPACE specifies that a space character (hexadecimal value; x’20’) is the overlay character. This is the default. |
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● |
is a character which does not overlay data
on lower-numbered input streams. |
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Streams used |
The following streams are used by the OVERLAY stage:
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Stream |
Action |
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Input streams |
OVERLAY reads records from each
connected input stream. |
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Primary output stream |
After reading a record from each of its
connected input streams, OVERLAY combines the records into a single output
record which it writes to its primary output stream. |
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Usage notes |
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1) |
OVERLAY delays one record. |
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2) |
If the OVERLAY stage discovers
that its primary output stream is not connected, the OVERLAY stage ends. |
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3) |
If a position in each input
stream contains the specified character, OVERLAY places that character in the
output record. |
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4) |
If a record in the
highest-numbered input stream is not as long as a lower-numbered input stream
record, OVERLAY writes the remaining characters from the lower-numbered input
stream records to the output stream. |
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5) |
If OVERLAY processes input
streams where one input stream does not have a record to compare, it compares
the records from the other streams. Consider the following streams: stream 0 contains 12 recordsstream 1 contains 14 recordsstream 2 contains 10 records
OVERLAY combines the first 10
records from all three streams and writes those records to its output stream.
Then it compares the 11th and 12th records of its
primary and secondary input streams and writes those two records to its
output stream. Finally, OVERLAY copies the 13th and 14th
records from its secondary input stream to its output stream. |
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6) |
OVERLAY reads a record from an
input stream, processes it, and then releases it before it reads a record
from the next highest input stream or writes to its output stream. |
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7) |
OVERLAY processes input records
until all input streams reach the end-of-file. |
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8) |
OVERLAY verifies that its
secondary output stream is not connected and then begins execution. |
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Examples |
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1) |
The following diagram shows two
input streams for OVERLAY and its resulting output stream, where char is SPACE; the default.
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2) |
This next diagram uses the same
input stream data, but specifies char
as A.
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See also |
Reference the following link for additional information:
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History of change |
None.
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