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80 lines
2.9 KiB
Forth
80 lines
2.9 KiB
Forth
\ KataDiversion in Forth
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\ -- utils
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\ empty the stack
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: EMPTY
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DEPTH 0 <> IF BEGIN
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DROP DEPTH 0 =
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UNTIL
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THEN ;
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\ power
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: ** ( n1 n2 -- n1_pow_n2 ) 1 SWAP ?DUP IF 0 DO OVER * LOOP THEN NIP ;
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\ compute the highest power of 2 below N.
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\ e.g. : 31 -> 16, 4 -> 4
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: MAXPOW2 ( n -- log2_n ) DUP 1 < IF 1 ABORT" Maxpow2 need a positive value."
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ELSE DUP 1 = IF 1
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ELSE
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1 >R
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BEGIN ( n |R: i=1)
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DUP DUP I - 2 *
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( n n 2*[n-i])
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R> 2 * >R ( … |R: i*2)
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> ( n n>2*[n-i] )
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UNTIL
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R> 2 /
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THEN
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THEN NIP ;
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\ -- kata
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\ test if the given N has two adjacent 1 bits
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\ e.g. : 11 -> 1011 -> -1
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\ 9 -> 1001 -> 0
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: ?NOT-TWO-ADJACENT-1-BITS ( n -- bool )
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\ the word uses the following algorithm :
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\ (stack|return stack)
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\ ( A N | X ) A: 0, X: N LOG2
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\ loop: if N-X > 0 then A++ else A=0 ; X /= 2
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\ return 0 if A=2
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\ if X=1 end loop and return -1
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0 SWAP DUP DUP 0 <> IF
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MAXPOW2 >R
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BEGIN
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DUP I - 0 >= IF
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SWAP DUP 1 = IF 1+ SWAP
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ELSE DROP 1 SWAP I -
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THEN
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ELSE NIP 0 SWAP
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THEN
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OVER
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2 =
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I 1 = OR
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R> 2 / >R
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UNTIL
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R> 2DROP
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2 <>
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ELSE 2DROP INVERT
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THEN ;
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\ return the maximum number which can be made with N (given number) bits
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: MAX-NB ( n -- m ) DUP 1 < IF DROP 0 ( 0 )
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ELSE
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DUP IF DUP 2 SWAP ** NIP 1 - ( 2**n - 1 )
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THEN
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THEN ;
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\ return the number of numbers which can be made with N (given number) bits
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\ or less, and which have not two adjacent 1 bits.
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\ see http://www.codekata.com/2007/01/code_kata_fifte.html
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: HOW-MANY-NB-NOT-TWO-ADJACENT-1-BITS ( n -- m )
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DUP 1 < IF DUP 0
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ELSE
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0 SWAP
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MAX-NB 1 + 0 DO I ?NOT-TWO-ADJACENT-1-BITS - LOOP
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THEN ;
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