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103 lines
2.2 KiB
Forth
103 lines
2.2 KiB
Forth
The `buffer:` words are one of the few direct holdovers
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from RETRO11. I use them frequently, but don't have a
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good single example or description. So let's rectify
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that now.
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A buffer is just a linear sequence of memory. These
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words provide a way to incrementally store or retrieve
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values from it.
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To begin, create a memory region to use as a buffer.
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~~~
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'Test d:create #1025 allot
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~~~
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Then you can set this as the current buffer:
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~~~
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Test buffer:set
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~~~
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When a buffer is set, the vocabulary sets an internal
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index to the first address in it. This will be
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incremented when you add data and decremented when you
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remove data.
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Let's add some stuff using `buffer:add`:
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~~~
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#100 buffer:add
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#200 buffer:add
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#300 buffer:add
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~~~
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And then retreive the values:
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~~~
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buffer:get n:put nl
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buffer:get n:put nl
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buffer:get n:put nl
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~~~
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You can remove all values using `buffer:empty`:
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~~~
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#100 buffer:add
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#200 buffer:add
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#300 buffer:add
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buffer:empty
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~~~
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And ask the buffer how many items it contains:
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~~~
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buffer:size n:put nl
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#100 buffer:add
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#200 buffer:add
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#300 buffer:add
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buffer:size n:put nl
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buffer:empty
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~~~
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The other functions are `buffer:start`, which returns
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the address of the buffer, `buffer:end`, which returns
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the address of the last value, and `buffer:preserve`.
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The first is easy to demo:
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~~~
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buffer:start Test eq? n:put nl
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~~~
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The last one is useful. Only one buffer is ever active
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at a given time. The `buffer:preserve` combinator lets
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you execute a word, saving and restoring the current
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buffer indexes. So the word could assign and use a new
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buffer and this will reset the previous one after
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control returns.
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There are a few notes that need to be considered. The
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preserve combinator saves the start and current index
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but *not* the contents. If the word you call uses the
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same buffer, the contents will remain altered.
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Finally, the buffer words have one interesting trait:
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they store an ASCII NULL after adding each item to the
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buffer. This lets one use them to build strings easily.
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~~~
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Test buffer:set
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$h buffer:add
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$e buffer:add
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$l buffer:add
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$l buffer:add
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$o buffer:add
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$, buffer:add
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#32 buffer:add
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$w buffer:add
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$o buffer:add
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$r buffer:add
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$l buffer:add
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$d buffer:add
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buffer:start s:put nl
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~~~
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