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CSI2P II Mini Project

Introduction

Let's consider a CPU, which has 32 bits registers r0-r255 and a 256 bytes memory.

In this project, you need to implement a binary expression calculator.

Input

The input will contain several binary expressions consisting of integers, operators, parentheses, and three variables x, y, and z.

The following operators will appear in this project:

  • +, -, *, /, %
  • =
  • ++, -- (including prefix and suffix, such as x++, --y, ... and so on)
  • +, - (expressions such as +x, -y, ... and so on)
  • others such as >>, +=, are unavailable and will not appear.

At most 15 lines per testcase, 195 characters per line.

  • That is, you don't have to change the value of MAX_LENGTH defined in the template.

Output

The output is a list of assembly codes. The instruction set architecture are listed in the table below.

If the input expressions contains illegal expression, you should handle it with the error handler. For the details, please refer to Error Handler below.

The input expression is a subset of C expression, which means you can treat the input as part of C codes and get the corresponding value of x, y, and z if you initialize them correctly. The result of x, y, and z solved by your assembly should be identical to the result of C described above.

You may refer to Sample section to see examples.

Instruction Set Architecture

Memory Operation

Opcode Operand1 Operand2 Meaning Cycles
load reg [Addr] Load data in memory [Addr] and save into register reg. 200
store [Addr] reg Store the data of register reg into memory [Addr]. 200

Arithmetic Operation

Opcode Operand1 Operand2 Operand3 Meaning Cycles
add rd rs1 rs2 Perform rs1+rs2 and save the result into rd. 10
sub rd rs1 rs2 Perform rs1-rs2 and save the result into rd. 10
mul rd rs1 rs2 Perform rs1*rs2 and save the result into rd. 30
div rd rs1 rs2 Perform rs1/rs2 and save the result into rd. 50
rem rd rs1 rs2 Perform rs1%rs2 and save the result into rd. 60
  • Note that both rs1 and rs2 can be a register or a non-negative integer. However, rd must be a valid register.
  • All operands should be separated by spaces.
  • Using the first 8 registers has no penalty. However, using other registers would double the instruction cycle.
    • For example, add r0 r1 r7 cost 10 cycles, while add r8 r0 r23 cost 20 cycles.

Identifiers

  • The initial value of variables x, y, and z are stored in memory [0], [4], and [8] respectively. Before you use them, you have to load them into registers first.
  • After the evaluation of the assembly code, the answer of the variables x, y, and z has to be stored in memory [0], [4], and [8] respectively.

Grammar

Expression grammar for mini project.

Start with "statement".

Note that this only checks syntactical error such as "x++++y". However, semantic error like "5++" or "1=2+3" will pass the grammar.

tokens:
    END:        ";"
    ASSIGN:     "="
    ADD:        "+"
    SUB:        "-"
    MUL:        "*"
    DIV:        "/"
    REM:        "%"
    PREINC:     "++"
    PREDEC:     "--"
    POSTINC:    "++"
    POSTDEC:    "--"
    PLUS:       "+"
    MINUS:      "-"
    IDENTIFIER: xyz
    CONSTANT:   123
    LPAR:       "("
    RPAR:       ")"

STMT
    → END
    | EXPR END
    ;
EXPR
    → ASSIGN_EXPR
    ;
ASSIGN_EXPR
    → ADD_EXPR
    | UNARY_EXPR ASSIGN ASSIGN_EXPR
    ;
ADD_EXPR
    → MUL_EXPR
    | ADD_EXPR ADD MUL_EXPR
    | ADD_EXPR SUB MUL_EXPR
    ;
MUL_EXPR
    → UNARY_EXPR
    | MUL_EXPR MUL UNARY_EXPR
    | MUL_EXPR DIV UNARY_EXPR
    | MUL_EXPR REM UNARY_EXPR
    ;
UNARY_EXPR
    → POSTFIX_EXPR
    | PREINC UNARY_EXPR
    | PREDEC UNARY_EXPR
    | PLUS UNARY_EXPR
    | MINUS UNARY_EXPR
    ;
POSTFIX_EXPR
    → PRI_EXPR
    | POSTFIX_EXPR POSTINC
    | POSTFIX_EXPR POSTDEC
    ;
PRI_EXPR
    → IDENTIFIER
    | CONSTANT
    | LPAR EXPR RPAR
    ;

Error Handler

The expression we designed is a subset of C expression statement. That is:

  • If this expression cannot be compiled by GCC, it's an illegal expression.
  • Our expression cannot be split into multiple lines, and there must be a ';' at the end of an instruction.

Illegal expressions such as:

  • x = 5++;

  • y = (((7/3);

  • z = ++(y++);

  • x = y 
  + 3;
  • and all expressions that cannot pass GCC compilers should be handled by error handler.

When an error occurs, no matter how much your assembly has outputted, your output must contain Compile Error! with newline.

Note that in our testcases, there won't be any undefined behavior expression. Such as:

  • 1/0 (divide by 0)
  • x = x++ (a variable updated twice or more in a single expression)
  • 2147483647+1 (signed overflow)
  • You may check if an expression is undefined behavior by compiling a C program with -Wall flag. If it is, there should be some warnings that shows the word "undefined", or refer to this site.

Assembly Compiler

ASMC - Assembly Compiler, which recognizes our ISA instructions as input, then parse them and output the value of x, y, z, and total CPU cycle. The input should end with EOF.

Note that ASMC is written in C++.

Prerequisites

C++ compiler that supports standard version c++11.

Compile

  • With command-line

    Run command:

    g++ -std=c++11 ASMC.cpp -o ASMC

    The executable file will be named as "ASMC".

  • With codeblocks

    1. Compile with codeblocks and execute.

Instruction

The initial value of (x, y, z) is (2, 3, 5). The final result of (x, y, z) will show up only when errors or EOF occur.

You are strongly recommended to use ASMC to debug.

With command-line, you can set the value of x, y, and z with given values by the following command:

./ASMC <x> <y> <z>

Replace <x>, <y>, and <z> with their initial values.

Sample

Sample Input 1

x = z + 5;

Sample Output 1

load r0 [8]
add r1 0 5
add r0 r0 r1
store [0] r0

If we initialize (x,y,z)=(2,3,5) and execute the input as part of C codes to see the value of x, y, and z, the result would be (x,y,z)=(10,3,5).

Feed the output into ASMC, you'll get the result of (x,y,z)=(10,3,5), which is identical to the result above, shows that the output is correct.

  • Total cycle cost: 200(load) + 2*10(add) + 200(store) = 420 cycles.

Sample Input 2

x = (y++) + (++z);
z = ++(y++);

Sample Output 2

load r255 [128]
Compile Error!
  • Note that in sample 2, the first expression is correct, while the second one causes compile error (semantic error).
  • The total cycle of compile error testcases will be recognized as 0.

Sample Input 3

7 + (x = (y = 3 * 5) % 9);
z = x * y;
z = 3;

Sample Output 3

add r0 0 6
store [0] r0
add r0 0 15
store [4] r0
add r0 1 2
store [8] r0
  • You don't actually need to keep the value of x, y, and z (i.e. [0], [4], and [8] in memory) correct after each expression, as long as the final result of x, y, and z is correct.
  • The instruction can be optimized, which means you can reduce the number of instructions while keeping the correctness of your answer as you wish.

Restrictions

Function itoa is not allowed. Please use sprintf instead.

  • Our judge system is linux-based system. itoa is not included in standard library. You'll receive compile error if you call itoa function.

Score

The project includes 2 parts:

  1. The 6 basic testcases, which will be provided by TAs.
  2. Contest: There will be 24 testcases at demo time. The first-six testcases are the same as basic testcases. Besides, the code with less total clock cycles is better. The top 10% will get extra points.

We will use ASMC and our mini project implementation to judge your code.

If your program runs more than 5 seconds in one testcase or exceeds 512MB in memory usage, you will get zero point at that testcase.