26 lines
2.4 KiB
Rexx
26 lines
2.4 KiB
Rexx
/*REXX program calculates and displays the fusc (or Stern's Diatomic) sequence. */
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parse arg st # xw . /*obtain optional arguments from the CL*/
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if st=='' | st=="," then st= 0 /*Not specified? Then use the default.*/
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if #=='' | #=="," then #= 61 /* " " " " " " */
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if xw=='' | xw=="," then xw= 0 /* " " " " " " */
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list= xw<1 /*boolean value: LIST to show numbers*/
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@.=; @.0= 0; @.1= 1 /*assign array default; assign low vals*/
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mL= 0 /*the maximum length (digits) so far. */
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$= /* " list of fusc numbers " " */
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do j=0 for # /*process a bunch of integers from zero*/
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if j>1 then if j//2 then do; _= (j-1) % 2; p= (j+1) % 2; @.j= @._ + @.p; end
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else do; _= j % 2; @.j= @._; end
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if list then if j>=st then $= $ commas(@.j) /*add it to a list*/
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else nop /*NOP≡placeholder.*/
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else do; if length(@.j)<=mL then iterate /*still too small.*/
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mL= length(@.j) /*found increase. */
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if mL==1 then say '═══index═══ ═══fusc number═══'
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say right( commas(j), 9) right( commas(@.j), 14)
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if mL==xw then leave /*Found max length? Then stop looking.*/
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end /* [↑] display fusc #s of maximum len.*/
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end /*j*/
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/*$ has a superfluous leading blank. */
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if $\=='' then say strip($) /*display a horizontal list of fusc #s.*/
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exit 0 /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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commas: parse arg ?; do _=length(?)-3 to 1 by -3; ?=insert(',', ?, _); end; return ?
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