CSE-111C++讨论

CSE-111 • Spring 2022 • Program 1 • Overloading and operators 1 of 7
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  1. Using C++11/14/17 (g++ -std=gnu++20)
    All programming in this course will be done C++ style, not C style.
    Do not use : Instead, use :
    char* strings
    C arrays
    , ,
    pointers or
    union inheritance or

    Include only C++ header files and use the declaration using namespace std; Include
    files only when C++ header files do not provide a necessary facility.
    Include files from C only when an appropriate file does not
    exist. Use the script cpplint.py.perl (a wrapper for cpplint.py) to check style.
    The production system for all work is unix.ucsc.edu using g++. Compile with
    g++ -std=gnu++20 -g -O0 -Wall -Wextra -Wpedantic -Wshadow -Wold-style-cast
    Following is a description of these options :
    • -std=gnu++20 Gnu dialect of C++20.
    • -g produces debugging information into object files and the binary executable.
    This is necessary for gdb and valgrind to use symbolic names.
    • -O0 reduces compilation time and makes debugging produce more expected
    results. Optimization may rearrange bugs in code in unexpected ways.
    • -Wall enables all the warnngs about questionable constructions.
    • -Wextra enables extra warnings that are not enabled with -Wall.
    • -Wpedantic issues all warnings required by strict ISO C++ and rejects all programs
    that do not conform to ISO C++.
    • -Wshadow warns whenever a local variable or declaration shadows another variable,
    parameter, or class member.
    • -Wold-style-cast warns about the use of any old-style (C-style) cast. Instead,
    use one of : static_cast, dynamic_cast, const_cast, reinterpret_cast. Better
    yet, code in suchaway as to not need casts.
    • -fdiagnostics-color=never prevents the compiler from using those silly annoying
    colors in diagnostics.
    The particular g++ compiler we will be using is
    -bash-1$ which g++
    /opt/rh/devtoolset-11/root/usr/bin/g++
    -bash-2$ g++ --version | grep -i g++
    g++ (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1)
    -bash-3$ uname -npo
    unix1.lt.ucsc.edu x86_64 GNU/Linux
    If you develop on your personal system, be sure to port and test your code on the
    Linux timeshares. If it compiles and runs on your system, but not on the timeshares,
    then it does not wor k.
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 2 of 7
  2. Overview
    This assignment will involve overloading basic integer operators to perform arbitrary
    precision integer arithmetic in the style of dc(1). Your class bigint will intermix
    arbitrarily with simple integer arithmetic.
    To begin read the man(1) page for the command dc(1) :
    man -s 1 dc
    A copy of that page is also in this directory. Your program will use the standard dc
    as a reference implemention and must produce exactly the same output for the
    commands you have to implement :
    +-*/%^cdfpq
    If you have any questions as to the exact format of your output, just run dc(1) and
    make sure that, for the operators specified above, your program produces exactly
    the same output. A useful program to compare output from your program with that
    of dc(1) is diff(1), which compares the contents of two files and prints only the differences.
    Also look in the subdirectory misc/ for some examples.
    See also :
    • dc (computer program)
    https://en.wikipedia.org/wiki...(computer_program)
    • dc, an arbitrary precision calculator
    https://www.gnu.org/software/...
  3. Implementation strategy
    As before, you have been given starter code.
    (a) Makefile, debug, and util If you find you need a function which does not properly
    belong to a given module, you may add it to util.
    (b) The module scanner reads in tokens, namely a NUMBER, an OPERATOR, or SCANEOF.
    Each token returns a token_t, which indicates what kind of token it is (the
    terminal_symbol symbol), and the string lexinfo associated with the token.
    Only in the case of a number is there more than one character. Note that on
    input, an underscore (_) indicates a negative number. The minus sign (-) is
    reserved only as a binary operator. The scanner also has defined a couple of
    operator<< for printing out scanner results in debug mode. This is strictly for
    debugging.
    (c) The main program main.cpp, has been implemented for you. For the six binary
    arithmetic functions, the right operand is popped from the stack, then the left
    operand, then the result is pushed onto the stack.
    (d) The module iterstack can not just be the STL stack, since we want to iterate
    from top to bottom, and the STL stack does not have an iterator. A stack
    depends on the operations back(), push_back(), and pop_back() in the underlying
    container. We could use a vector, a deque, or just a list, as long as the requisite
    operations are available.
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 3 of 7
  4. Class bigint
    Then we come to the most complex part of the assignment, namely the class bigint.
    Operators in this class are heavily overloaded.
    (a) Most of the functions take a arguments of type const bigint&, i.e., a constant
    reference, for the sake of efficiency. But they have to return the result by
    value.
    (b) The operator<< can’t be a member since its left operand is an ostream, so we
    make it a friend, so that it can see the innards of a bigint. Note now dc prints
    really big numbers. operator<< is used by debugging functions.
    (c) The function print (suitably modified) is used for actual output.
    (d) The relational operators == and < are coded individually as member functions.
    The others, !=, <=, >, and >= are defined in terms of the essential two.
    (e) All of the functions of bigint only work with the sign, using ubigint to do the
    actual computations. So bigint::operator+ and bigint::operator- will check
    the signs of the two operands then call ubigint::operator+ or ubigint::operator-,
    as appropriate, depending on the relative signs and magnitudes. The
    multiplication and division operators just call the corresponding ubigint operators,
    then adjust the resulting sign according to the rule of signs.
  5. Class ubigint
    Class ubigint implements unsigned large integers and is where the computational
    work takes place. Class bigint takes care of the sign. Now we turn to the representation
    of a ubigint, which will be represented by vector of bytes.
    (a) Replace the declaration
    using ubigvalue_t = unsigned long;
    with
    using ubigvalue_t = vector;
    in the header file . The type uint8_t is an unsigned 8-bit integer
    defined in .
    (b) In storing the big integer, each digit is kept as an integer in the range 0 to 9 in
    an element of the vector. Since the arithmetic operators add and subtract
    work from least significant digit to most significant digit, store the elements of
    the vector in the same order. That means, for example, that the number 4629
    would be stored in a vector v as : v[3]==4, v[2]==6, v[1]==2, v[0]==9. In other
    words, if v[k]==d, then the digit’s place value is d*pow(10,k). In mathematical
    notation, the value of a radix 10 (base 10) number v with n digits is :
    n−1
    i=0
    Σ vi10i
    = vn−110n−1
  6. vn−210n−2
  7. ... + v2102
  8. v1101
  9. v0100
    (c) In order for the comparisons to work correctly, always store numbers in a
    canonical form : After computing a value from any one of the six arithmetic
    operators, always trim the vector by removing all high-order zeros :
    while (size() > 0 and back() == 0) pop_back();
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 4 of 7
    (d) Canonical form.
    • Zero is represented as a vector of size zero and a positive sign.
    • High-order zeros are suppressed.
    • All digits are stored as uint8_t values in the range 0...9, not as characters in
    the range ’0’...’9’.
    • To print a digit, cast it to an integer : cout << static_cast (digit).
    • This can be done more easily by : cout << int (digit), which looks like a
    ctor call.
    (e) The scanner will produce numbers as strings, so scan each string from the end
    of the string, using a const_reverse_iterator (or other means) from the end of
    the string (least significant digit) to the beginning of the string (most signifi-
    cant digit) using push_back to append them to the vector.
  10. Implementation of operators
    (a) For bigint::operator+, check the signs.
    (1) If the signs are the same :
    • Call ubigint::operator+ with the unsigned numbers.
    • The sign of the result is the sign of either number.
    (2) If the signs are different :
    • Call ubigint::operator- with the larger number as its left number.
    • The sign of the result is the sign of the larger number.
    (b) The operator bigint::operator-, check the signs.
    (1) If the signs are different :
    • Call ubigint::operator+ with the unsigned numbers.
    • The sign of the result is the sign of the left number.
    (2) If the signs are the same :
    • Call ubigint::operator- with the larger number as its left number.
    • If the left number is larger, the sign of the result is its sign.
    • Else the the result has the opposite of the sign of the right number.
    (c) For the above bigint::operator+ and bigint::operator-, to find the ‘‘larger’’
    number, make use of ubigint::operator<. Since the numbers are kept in
    canonical form (see above), to compare them :
    (1) Check the size() of each vector. If different, the larger number has the
    greater size.
    (2) If the sizes are the same, write a loop iterating from the highest-order
    digit toward the lowest-order digit, comparing digit by digit.
    • As soon as a difference is found, return true or false, as appriate.
    • If all digits are the same, then return false.
    (d) To implement ubigint::operator+, create a new ubigint and proceed from the
    low order end to the high order end, adding digits pairwise. For any sum >=
    10, take the remainder and add the carry to the next digit. Use push_back to
    append the new digits to the ubigint. When you run out of digits in the
    shorter number, continue, matching the longer vector with zeros, until it is
    done. Make sure the sign of 0 is positive.
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 5 of 7
    (e) To implement ubigint::operator-, also create a new empty vector, starting
    from the low order end and continuing until the high end. If the left digit is
    smaller than the right digit, the subtraction will be less than zero. In that
    case, add 10 to the digit, and set the borrow to the next digit to −1. After the
    algorithm is done, pop_back all high order zeros from the vector before returning
    it. Make sure the sign of 0 is positive.
    (f) To implement bigint::operator==, check to see if the signs are the same and
    ubigint::operator== returns true.
    (g) To implement ubigint::operator==, just use the vector::operator== comparison
    function.
    (h) To implement bigint::operator<, remember that a negative number is less
    than a positive number. If the signs are the same, use ubigint::operator< for
    a comparison. For positive numbers, the smaller one is less. and for negative
    nubmers, the larger one is less.
    (i) To implement ubigint::operator<, check the size() of each vector. The
    shorter one is less than the longer one. If the size() are the same, scan the
    vectors in parallel from the most significant digit to the last significant digit
    until a difference is found.
    (j) Implement function bigint::operator*, which uses the rule of signs to determine
    the result. The number crunching is delegated to ubigint::operator*,
    which produces the unsigned result.
    (k) Multiplication in ubigint::operator* proceeds by allocating a new vector
    whose size is equal to the sum of the sizes of the other two operands. If u is a
    vector of size m and v is a vector of size n, then in O(mn) speed, perform an outer
    loop over one argument and an inner loop over the other argument, adding the
    new partial products to the product p as you would by hand. The algorithm
    can be described as follows :
    p=all zeros
    for i in interval [0,m):
    carry = 0
    for j in interval [0,n):
    digit = p[i+j] + u[i] * v[j] + carry
    p[i+j] = digit % 10
    carry = digit / 10
    p[i+n] = carry
    Note that the interval [a,b) refers to the half-open interval including a but
    excluding b. This is the set {x| a<=x && xin C++ is used to bound an interval (begin and end pair).
    (l) Long division is complicated if done correctly. See a paper by P. Brinch
    Hansen, ‘‘Multiple-length division revisited : A tour of the minefield’’, Software
    — Practice and Experience 24, (June 1994), 579–601. Algorithms 1 to 12 are
    on pages 13–23, Note that in Pascal, array bounds are part of the type, which
    is not true for vectors in C++.
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 6 of 7
    • multiple-length-division.pdf
    http://brinch-hansen.net/pape...
    http://citeseerx.ist.psu.edu/...
    (m) The function divide as implemented uses the ancient Egyptian division algorithm,
    which is slower than Hansen’s Pascal program, but is easier to understand.
    Replace the long values in it by vector. The logic is shown
    also in misc/divisioncpp.cpp. The algorithm is rather slow, but the big-O
    analysis is reasonable.
    (n) The unsigned division function that is provided depends on two private functions,
    multiply_by_2 and divide_by_2, which are in-lace non-constant functions.
    They both perform without creating a new object.
    (1) To implement multiply_by_2, iterate from the low order digit, and double
    each digit (remainder 10), carrying to the next higher digit. At the end, if
    the carry is 1, use push_back.
    (2) To implement divide_by_2, iterate from the low order digit, and divide
    each digit by 2. Then, if the next higher digit is odd, add 5 to the current
    digit. Be careful of the end, and pop_back any remaining high order
    zeros.
    (o) Modify operator<<, first just to print out the number all in one line. You will
    need this to debug your program.
    (p) The function print will print numbers in the same way as dc(1) does.
    (q) The pow function uses other operations to raise a number to a power. If the
    exponent does not fit into a single long print an error message, otherwise do
    the computation. The power function is not a member of either bigint or ubigint,
    and is just considered a library function that is implemented using more
    primitive operations.
  11. Memory leak and other problems
    Make sure that you test your program completely so that it does not crash on a Segmentation
    Fault or any other unexpected error. Since you are not using pointers,
    and all values are inline, there should be no memory leak. Use valgrind(1) to check
    for and eliminate uninitialized variables and memory leak.
    If your program is producing strange output or segmentation faults, use gdb(1) and
    the debug macros in the debug module of the code/ subdirectory.
  12. What to submit
    Submit source files and only source files : Makefile, README, and all of the header
    and implementation files necessary to build the target executable. If gmake does not
    build ydc your program can not be tested and you lose 1/2 of the points for the
    assignment. Use checksource on your code to verify basic formatting.
    Look in the grader’s score subdirectory for instructions to graders. Read Syllabus/
    pair-programming/ and also submit PARTNER if you are doing pair programming.
    Either way submit the README described therein.
    CSE-111 • Spring 2022 • Program 1 • Overloading and operators 7 of 7
  13. Et cetera (και τα ‘´ετερα).
    The accuracy of the Unix utility dc(1) can be checked by :
    echo ’82 43/25 43+65P80P82P73P76P32P70P79P79P76P10P’ | dc

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