CSCI 2021 Lab05: Shifting and Masking

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                            LAB 05 QUESTIONS
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Lab Instructions
================

  Follow the instructions below to experiment with topics related to
  this lab.
  - For sections marked QUIZ, fill in an (X) for the appropriate
    response in this file. Use the command `make test-quiz' to see if
    all of your answers are correct.
  - For sections marked CODE, complete the code indicated. Use the
    command `make test-code' to check if your code is complete.
  - DO NOT CHANGE any parts of this file except the QUIZ sections as it
    may interfere with the tests otherwise.
  - If your `QUESTIONS.txt' file seems corrupted, restore it by copying
    over the `QUESTIONS.txt.bk' backup file.
  - When you complete the exercises, check your answers with `make test'
    and if all is well, create a zip file with `make zip' and upload it
    to Gradescope. Ensure that the Autograder there reflects your local
    results.
  - IF YOU WORK IN A GROUP only one member needs to submit and then add
    the names of their group.


QUIZ mask.c
===========

  Study the code in `masking.c' which uses a number of bit-wise
  operations that have recently been discussed in lecture. These
  include:
  ,----
  | | Operation | Description          |
  | |-----------+----------------------|
  | | x & y     | Bit-wise And         |
  | | x | y     | Bit-wise Or          |
  | | x ^ y     | Bit-wise Xor         |
  | | ~x        | Bit-wise inversion   |
  | | x << y    | Bit-wise Left-shift  |
  | | x >> y    | Bit-wise Right-shift |
  `----
  Study the examples provided in `masking.c' and ensure you understand
  their meaning according to the context provided. Then answer the
  following questions.


Terminology
~~~~~~~~~~~

  - "Setting" a given bit means to place a 1 that position; "Set bit 7"
    means to ensure that the 7th bit from the left is a 1
  - "Clearing" a give bit means to place a 0 at that position; "Clear
    bit 7" means to ensure that the 7th bit from the left is a 0


Shift with Or
~~~~~~~~~~~~~

  What is the effect of the following line of code:
  ,----
  | x = x | (1 << 19);
  `----

  - ( ) Changes `x' so that only its 19th bit is a 1, all other bits are
    0.
  - ( ) Changes `x' so that only its 19th bit is a 0, all other bits are
    unchanged.
  - ( ) Changes `x' so that its 19th bit is set to 1, all other bits
    unchanged.
  - ( ) Changes `x' so that its bits are shifted left by 19 places.


Shift with Or with Pattern
~~~~~~~~~~~~~~~~~~~~~~~~~~

  If `x' is cleared (value all 0's), what is the effect of the following
  line of code:
  ,----
  | x = x | (0b110101 << 8);
  `----

  - ( ) Sets the bits of `x' to the given pattern `0b110101' starting
    with the 8th position.
  - ( ) Checks that `x' has the given pattern `0b110101' starting with
    the 8th position.
  - ( ) Copies the given pattern `0b110101' 8 times throughout `x'
  - ( ) Adds 53 on the value of `x' faster than normal addition.


Shift with Invert with And
~~~~~~~~~~~~~~~~~~~~~~~~~~

  What is the effect of the following line of code:
  ,----
  | x = x & ~(1 << 8);
  `----

  - ( ) Changes `x' so that only its 8th bit is a 1, all other bits are
    0.
  - ( ) Changes `x' so that only its 8th bit is a 0, all other bits are
    unchanged.
  - ( ) Changes `x' so that its 8th bit is set to 1, all other bits
    unchanged.
  - ( ) Changes `x' so that its bits are shifted left by 8 places.


Shift with And
~~~~~~~~~~~~~~

  What is the effect of the following line of code:
  ,----
  | if( x & (1 << 13) ){ ... }
  `----

  - ( ) Conditionally execute only if the 13th bit of `x' is 0 and set
    that bit subsequently.
  - ( ) Conditionally execute only if the 13th bit of `x' is 0 but leave
    `x' unchanged.
  - ( ) Conditionally execute only if the 13th bit of `x' is 1 and set
    that bit subsequently.
  - ( ) Conditionally execute only if the 13th bit of `x' is 1 but leave
    `x' unchanged.


CODE Complete masking.c
=======================

  Complete the TODO items in the `masking.c' file so that the missing
  blocks produce the effect mentioned in the `printf()' statements.

  Test that the code behaves correctly via the command
  ,----
  | make test-code
  `----

  and verify that both code/quiz are correct via
  ,----
  | make test
  `----

  before using
  ,----
  | make zip
  `----

  to create a zip to submit.