mirror of
https://git.sr.ht/~crc_/retroforth
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69 lines
1.7 KiB
Forth
69 lines
1.7 KiB
Forth
# Float
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## Description
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This implements a means of encoding floating point values into signed
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integer cells. The technique is described in the paper titled "Encoding
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floating point numbers to shorter integers" by Kiyoshi Yoneda and
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Charles Childers.
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This will extend the `f:` vocabulary and adds a new `u:` vocabulary.
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## Code & Commentary
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Define some constants. The range is slightly reduced from the standard
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integer range as the smallest value is used for NaN.
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~~~
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n:MAX n:dec 'u:MAX const
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n:MAX n:dec n:negate 'u:MIN const
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n:MIN 'u:NAN const
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n:MAX 'u:INF const
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n:MAX n:negate 'u:-INF const
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~~~
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~~~
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:u:n? (u-f)
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u:MIN n:inc u:MAX n:dec n:between? ;
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:u:max? (u-f) u:MAX eq? ;
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:u:min? (u-f) u:MIN eq? ;
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:u:zero? (u-f) n:zero? ;
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:u:nan? (u-f) u:NAN eq? ;
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:u:inf? (u-f) u:INF eq? ;
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:u:-inf? (u-f) u:-INF eq? ;
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:u:clip (u-u) u:MIN u:MAX n:limit ;
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~~~
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~~~
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{{
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:s .10.0e-4 ;
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:f:encode .0.5 f:power s .-1.0 f:power f:* ;
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:f:decode f:square s f:square f:* ;
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---reveal---
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:f:to-u (-u|f:a-)
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f:dup f:encode f:round f:to-number u:clip
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f:dup f:nan? [ drop u:NAN ] if
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f:dup f:inf? [ drop u:INF ] if
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f:dup f:-inf? [ drop u:-INF ] if
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f:drop ;
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:u:to-f (u-|f:-b)
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dup n:to-float f:decode
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dup u:nan? [ f:drop f:NAN ] if
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dup u:inf? [ f:drop f:INF ] if
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dup u:-inf? [ f:drop f:-INF ] if
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drop ;
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}}
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~~~
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```
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:tab #9 c:put #9 c:put #9 c:put ;
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.103.333 f:to-u dup n:put tab u:to-f f:put nl
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..000412 f:to-u dup n:put sp sp tab u:to-f f:put nl
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.129192.232415 f:to-u dup n:put tab u:to-f f:put nl
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f:NAN f:to-u dup n:put sp sp sp sp sp u:to-f f:put nl
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f:INF f:to-u dup n:put sp sp sp sp sp u:to-f f:put nl
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```
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