The following pseudocode helps to illustrate how a column is allocated, then deallocated, then allocated again.
When this pseudocode executes, column C is allocated when the invoke statement of line 6 executes. It is deallocated at the end of the subroutine. However, the same column is re-allocated when the subroutine is invoked again on line 8.
A | B | C | Explanation |
line# | x |
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pre | ? |
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| 5 | 4 |
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| 6 | retline# | ||
| 7 |
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| 2 | 5 | ||
| 3 | retline# | At this point, column C is deallocated, making it the leftmost available column again. |
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| 7 | 15 |
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| 8 | retline# | Because column C is the leftmost available column, it is allocated again for the purpose of storing the return line number. |
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| post | The actual return line number is different this time. |
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| 2 | 16 |
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| 3 | retline# | ||
post |
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