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Task/Balanced-ternary/Liberty-BASIC/balanced-ternary.basic

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+global tt$
+tt$="-0+"   '-1 0 1; +2 -> 1 2 3, instr
+
+'Test case:
+'With balanced ternaries a from string "+-0++0+", b from native integer -436, c "+-++-":
+'* write out a, b and c in decimal notation;
+'* calculate a * (b - c), write out the result in both ternary and decimal notations.
+
+a$="+-0++0+"
+a=deci(a$)
+print "a",a, a$
+
+b=-436
+b$=ternary$(b)
+print "b",b, b$
+
+c$="+-++-"
+c=deci(c$)
+print "c",c, c$
+
+'calculate in ternary
+
+res$=multTernary$(a$, subTernary$(b$, c$))
+print "a * (b - c)", res$
+print "In decimal:",deci(res$)
+
+print "Check:"
+print "a * (b - c)", a * (b - c)
+end
+
+function deci(s$)
+    pow = 1
+    for i = len(s$) to 1 step -1
+        c$ = mid$(s$,i,1)
+        'select case c$
+        '    case "+":sign= 1
+        '    case "-":sign=-1
+        '    case "0":sign= 0
+        'end select
+        sign = instr(tt$,c$)-2
+        deci = deci+pow*sign
+        pow = pow*3
+    next
+end function
+
+function ternary$(n)
+    while abs(n)>3^k/2
+        k=k+1
+    wend
+    k=k-1
+
+    pow = 3^k
+    for i = k to 0 step -1
+        sign = (n>0) - (n<0)
+        sign = sign * (abs(n)>pow/2)
+        ternary$ = ternary$+mid$(tt$,sign+2,1)
+        n = n - sign*pow
+        pow = pow/3
+    next
+    if  ternary$ = "" then  ternary$ ="0"
+end function
+
+function multTernary$(a$, b$)
+
+    c$ = ""
+    t$ = ""
+    shift$ = ""
+    for i = len(a$) to 1 step -1
+
+        select case mid$(a$,i,1)
+        case "+": t$ = b$
+        case "0": t$ = "0"
+        case "-": t$ = negate$(b$)
+        end select
+
+        c$ = addTernary$(c$, t$+shift$)
+
+        shift$ = shift$ +"0"
+    'print d, t$, c$
+    next
+    multTernary$ = c$
+end function
+
+function subTernary$(a$, b$)
+     subTernary$ = addTernary$(a$, negate$(b$))
+end function
+
+function negate$(s$)
+    negate$=""
+    for i = 1 to len(s$)
+        'print mid$(s$,i,1), instr(tt$, mid$(s$,i,1)), 4-instr(tt$, mid$(s$,i,1))
+        negate$=negate$+mid$(tt$, 4-instr(tt$, mid$(s$,i,1)), 1)
+    next
+end function
+
+function addTernary$(a$, b$)
+'add a$ + b$, for now only positive
+    l = max(len(a$), len(b$))
+    a$=pad$(a$,l)
+    b$=pad$(b$,l)
+    c$ = "" 'result
+    carry = 0
+    for i = l to 1 step -1
+        a = instr(tt$,mid$(a$,i,1))-2
+        b = instr(tt$,mid$(b$,i,1))-2     '-1 0 1
+        c = a+b+carry
+
+        select case
+        case abs(c)<2
+            carry = 0
+        case c>0
+            carry =1: c=c-3
+        case c<0
+            carry =-1: c=c+3
+        end select
+
+        'print a, b, c
+        c$ = mid$(tt$,c+2,1)+c$
+    next
+    if carry<>0 then c$ = mid$(tt$,carry+2,1) +c$
+    'print c$
+    'have to trim leading 0's
+    i=0
+    while mid$(c$,i+1,1)="0"
+        i=i+1
+    wend
+    c$=mid$(c$,i+1)
+    if c$="" then c$="0"
+    addTernary$ = c$
+end function
+
+function pad$(a$,n)  'pad from right with 0 to length n
+     pad$ = a$
+     while len(pad$)<n
+        pad$ = "0"+pad$
+     wend
+end function