30 lines
2.4 KiB
Rexx
30 lines
2.4 KiB
Rexx
/*REXX program displays (all) the sums of a full 4─bit adder (with carry). */
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call hdr1; call hdr2 /*note the order of headers & trailers.*/
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/* [↓] traipse thru all possibilities.*/
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do j=0 for 16
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do m=0 for 4; a.m=bit(j, m); end /*m*/
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do k=0 for 16
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do m=0 for 4; b.m=bit(k, m); end /*m*/
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sc=4bitAdder(a., b.)
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z=a.3 a.2 a.1 a.0 '_+_' b.3 b.2 b.1 b.0 "_=_" sc ',' s.3 s.2 s.1 s.0
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say translate(space(z, 0), , '_') /*remove all the underbars (_) from Z. */
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end /*k*/
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end /*j*/
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call hdr2; call hdr1 /*display two trailers (note the order)*/
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exit /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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bit: procedure; parse arg x,y; return substr( reverse( x2b( d2x(x) ) ), y+1, 1)
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halfAdder: procedure expose c; parse arg x,y; c=x & y; return x && y
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hdr1: say 'aaaa + bbbb = c, sum [c=carry]'; return
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hdr2: say '════ ════ ══════' ; return
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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fullAdder: procedure expose c; parse arg x,y,fc
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_1=halfAdder(fc, x); c1=c
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_2=halfAdder(_1, y); c=c | c1; return _2
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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4bitAdder: procedure expose s. a. b.; carry.=0
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do j=0 for 4; n=j-1
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s.j=fullAdder(a.j, b.j, carry.n); carry.j=c
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end /*j*/
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return c
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