4位ALU逻辑运算器，用VHDL语言编写-4-bit ALU process using VHDL

This 4-Bit ALU performs four below operations: 00 (S14=0 & S04=0) : OR 01 (S14=0 & S04=1) : AND 10 (S14=1 & S04=0) : ADD 11 (S14=1 & S04=1) : SUB

a 4 BIT alu implemented using vhdl as core language. Works fine on spartan 3e. tested and verified