Ethiopian multiplication: Difference between revisions
Added XPL0
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;pretty small, just 24 bytes </lang>
=={{header|XPL0}}==
<lang XPL0>include c:\cxpl\codes; \intrinsic 'code' declarations
func Halve(N); \Return half of N
int N;
return N>>1;
func Double(N); \Return N doubled
int N;
return N<<1;
func IsEven(N); \Return 'true' if N is an even number
int N;
return (N&1)=0;
func EthiopianMul(A, B); \Multiply A times B using Ethiopian method
int A, B;
int I, J, S, Left(100), Right(100);
[Left(0):= A; Right(0):= B; \1. write numbers to be multiplied
I:= 1; \2. repeatedly halve number on left
repeat A:= Halve(A);
Left(I):= A; I:= I+1;
until A=1;
J:= 1; \3. repeatedly double number on right
repeat B:= Double(B);
Right(J):= B; J:= J+1;
until J=I; \stop where left column = 1
for J:= 0 to I-1 do \4. discard right value if left is even
if IsEven(Left(J)) then Right(J):= 0;
S:= 0; \5. sum remaining values on right
for J:= 0 to I-1 do
S:= S + Right(J);
for J:= 0 to I-1 do \show this insanity
[IntOut(0, Left(J)); ChOut(0, 9\tab\); IntOut(0, Right(J)); CrLf(0)];
Text(0, " --------
");
return S; \sum = product
];
int Product;
[Product:= EthiopianMul(17, 34);
ChOut(0, 9); IntOut(0, Product); CrLf(0); CrLf(0);
Product:= EthiopianMul(1234, 5678);
ChOut(0, 9); IntOut(0, Product); CrLf(0);
]</lang>
{{out}}
<pre>
17 34
8 0
4 0
2 0
1 544
--------
578
1234 0
617 11356
308 0
154 0
77 90848
38 0
19 363392
9 726784
4 0
2 0
1 5814272
--------
7006652
</pre>
[[Category:Arithmetic]]
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