http://en.wikipedia.org/wiki/Multiplication_ALU
1011 (this is 11 in decimal)
x 1110 (this is 14 in decimal)
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0000 (this is 1011 x 0)
1011 (this is 1011 x 1, shifted one position to the left)
1011 (this is 1011 x 1, shifted two positions to the left)
+ 1011 (this is 1011 x 1, shifted three positions to the left)
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10011010 (this is 154 in decimal)
乘以2 相当于二进制各位左移一位后右补0
遇到偶数(二进制末位为0)把中间和删掉,相当于乘以二进制0