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            You are to write an interpreter for a simple computer. This computer uses a processor with a small number of machine instructions. Furthermore, it is equipped with 32 byte of memory, one 8-bit accumulator (accu) and a 5-bit program counter (pc). The memory contains data as well as code, which is the usual von Neumann architecture.

            The program counter holds the address of the instruction to be executed next. Each instruction has a length of 1 byte - the highest 3 bits define the type of instruction and the lowest 5 bits define an optional operand which is always a memory address (xxxxx). For instructions that don't need an operand the lowest 5 bits have no meaning (-----). Here is a list of the machine instructions and their semantics:

            000xxxxx   STA x   store the value of the accu into memory byte x
            001xxxxx   LDA x   load the value of memory byte x into the accu
            010xxxxx   BEQ x   if the value of the accu is 0 load the value x into the pc
            011-----   NOP     no operation
            100-----   DEC     subtract 1 from the accu
            101-----   INC     add 1 to the accu
            110xxxxx   JMP x   load the value x into the pc
            111-----   HLT     terminate program

            In the beginning, program counter and accumulator are set to 0. After fetching an instruction but before its execution, the program counter is incremented. You can assume that programs will terminate.

            Input Specification

            The input file contains several test cases. Each test case specifies the contents of the memory prior to execution of the program. Byte 0 through 31 are given on separate lines in binary representation. A byte is denoted by its highest-to-lowest bits. Input is terminated by EOF.

            Output Specification

            For each test case, output on a line the value of the accumulator on termination in binary representation, again highest bits first.

            Sample Input

            00111110
                        10100000
                        01010000
                        11100000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00111111
                        10000000
                        00000010
                        11000010
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        00000000
                        11111111
                        10001001
                        

            Sample Output

            10000111
            很好的題,很容易錯。
            需要計算機組成原理的一點知識,沒學過也能做。
            指令譯碼,(將二進制轉化為十進制并從中獲得操作類型和立即數x)可以用位運算,
            指令執行 pc,accu,立即數x都可以用int表示且是全局變量,memory用數組表示。
            有很多注意的地方,
            pc不能超過32;不能小于0.
            accu不能超過256.不能小于0.
            自己都沒有注意到。
            pc,accu,
            posted on 2009-07-24 10:59 luis 閱讀(305) 評論(0)  編輯 收藏 引用 所屬分類: 粗心題
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