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-// ----------------------------------------------------------------------------
-// Quiz Time: Toggling, Setting, and Clearing Bits
-// ----------------------------------------------------------------------------
-//
-// Another exciting thing about Zig is its suitability for embedded
-// programming. Your Zig code doesn't have to remain on your laptop; you can
-// also deploy your code to microcontrollers! This means you can write Zig to
-// drive your next robot or greenhouse climate control system! Ready to enter
-// the exciting world of embedded programming? Let's get started!
-//
-// ----------------------------------------------------------------------------
-// Some Background
-// ----------------------------------------------------------------------------
-//
-// A common activity in microcontroller programming is setting and clearing
-// bits on input and output pins. This lets you control LEDs, sensors, motors
-// and more! In a previous exercise (097_bit_manipulation.zig) you learned how
-// to swap two bytes using the ^ (XOR - exclusive or) operator. This quiz will
-// test your knowledge of bit manipulation in Zig while giving you a taste of
-// what it's like to control registers in a real microcontroller. Included at
-// the end are some helper functions that demonstrate how we might make our
-// code a little more readable.
-//
-// Below is a pinout diagram for the famous ATmega328 AVR microcontroller used
-// as the primary microchip on popular microcontroller platforms like the
-// Arduino UNO.
-//
-//  ============ PINOUT DIAGRAM FOR ATMEGA328 MICROCONTROLLER ============
-//                                _____ _____
-//                               |     U     |
-//                 (RESET) PC6 --|  1     28 |-- PC5
-//                         PD0 --|  2     27 |-- PC4
-//                         PD1 --|  3     26 |-- PC3
-//                         PD2 --|  4     25 |-- PC2
-//                         PD3 --|  5     24 |-- PC1
-//                         PD4 --|  6     23 |-- PC0
-//                         VCC --|  7     22 |-- GND
-//                         GND --|  8     21 |-- AREF
-//                     |-- PB6 --|  9     20 |-- AVCC
-//                     |-- PB7 --| 10     19 |-- PB5 --|
-//                     |   PD5 --| 11     18 |-- PB4 --|
-//                     |   PD6 --| 12     17 |-- PB3 --|
-//                     |   PD7 --| 13     16 |-- PB2 --|
-//                     |-- PB0 --| 14     15 |-- PB1 --|
-//                     |         |___________|         |
-//                     \_______________________________/
-//                                    |
-//                                  PORTB
-//
-// Drawing inspiration from this diagram, we'll use the pins for PORTB as our
-// mental model for this quiz on bit manipulation. It should be noted that
-// in the following problems we are using ordinary variables, one of which we
-// have named PORTB, to simulate modifying the bits of real hardware registers.
-// But in actual microcontroller code, PORTB would be defined something like
-// this:
-//          pub const PORTB = @as(*volatile u8, @ptrFromInt(0x25));
-//
-// This lets the compiler know not to make any optimizations to PORTB so that
-// the IO pins are properly mapped to our code.
-//
-// NOTE : To keep things simple, the following problems are given using type
-// u4, so applying the output to PORTB would only affect the lower four pins
-// PB0..PB3. Of course, there is nothing to prevent you from swapping the u4
-// with a u8 so you can control all 8 of PORTB's IO pins.
-
-const std = @import("std");
-const print = std.debug.print;
-const testing = std.testing;
-
-pub fn main() !void {
-    var PORTB: u4 = 0b0000; // only 4 bits wide for simplicity
-
-    // ------------------------------------------------------------------------
-    // Quiz
-    // ------------------------------------------------------------------------
-
-    // See if you can solve the following problems. The last two problems throw
-    // you a bit of a curve ball. Try solving them on your own. If you need
-    // help, scroll to the bottom of main to see some in depth explanations on
-    // toggling, setting, and clearing bits in Zig.
-
-    print("Toggle pins with XOR on PORTB\n", .{});
-    print("-----------------------------\n", .{});
-    PORTB = 0b1100;
-    print("  {b:0>4} // (initial state of PORTB)\n", .{PORTB});
-    print("^ {b:0>4} // (bitmask)\n", .{0b0101});
-    PORTB ^= (1 << 1) | (1 << 0); // What's wrong here?
-    checkAnswer(0b1001, PORTB);
-
-    newline();
-
-    PORTB = 0b1100;
-    print("  {b:0>4} // (initial state of PORTB)\n", .{PORTB});
-    print("^ {b:0>4} // (bitmask)\n", .{0b0011});
-    PORTB ^= (1 << 1) & (1 << 0); // What's wrong here?
-    checkAnswer(0b1111, PORTB);
-
-    newline();
-
-    print("Set pins with OR on PORTB\n", .{});
-    print("-------------------------\n", .{});
-
-    PORTB = 0b1001; // reset PORTB
-    print("  {b:0>4} // (initial state of PORTB)\n", .{PORTB});
-    print("| {b:0>4} // (bitmask)\n", .{0b0100});
-    PORTB = PORTB ??? (1 << 2); // What's missing here?
-    checkAnswer(0b1101, PORTB);
-
-    newline();
-
-    PORTB = 0b1001; // reset PORTB
-    print("  {b:0>4} // (reset state)\n", .{PORTB});
-    print("| {b:0>4} // (bitmask)\n", .{0b0100});
-    PORTB ??? (1 << 2); // What's missing here?
-    checkAnswer(0b1101, PORTB);
-
-    newline();
-
-    print("Clear pins with AND and NOT on PORTB\n", .{});
-    print("------------------------------------\n", .{});
-
-    PORTB = 0b1110; // reset PORTB
-    print("  {b:0>4} // (initial state of PORTB)\n", .{PORTB});
-    print("& {b:0>4} // (bitmask)\n", .{0b1011});
-    PORTB = PORTB & ???@as(u4, 1 << 2); // What character is missing here?
-    checkAnswer(0b1010, PORTB);
-
-    newline();
-
-    PORTB = 0b0111; // reset PORTB
-    print("  {b:0>4} // (reset state)\n", .{PORTB});
-    print("& {b:0>4} // (bitmask)\n", .{0b1110});
-    PORTB &= ~(1 << 0); // What's missing here?
-    checkAnswer(0b0110, PORTB);
-
-    newline();
-    newline();
-}
-
-// ************************************************************************
-//                    IN-DEPTH EXPLANATIONS BELOW
-// ************************************************************************
-//
-//
-//
-//
-//
-//
-//
-//
-//
-//
-//
-// ------------------------------------------------------------------------
-// Toggling bits with XOR:
-// ------------------------------------------------------------------------
-// XOR stands for "exclusive or". We can toggle bits with the ^ (XOR)
-// bitwise operator, like so:
-//
-//
-// In order to output a 1, the logic of an XOR operation requires that the
-// two input bits are of different values. Therefore, 0 ^ 1 and 1 ^ 0 will
-// both yield a 1 but 0 ^ 0 and 1 ^ 1 will output 0. XOR's unique behavior
-// of outputting a 0 when both inputs are 1s is what makes it different from
-// the OR operator; it also gives us the ability to toggle bits by putting
-// 1s into our bitmask.
-//
-// - 1s in our bitmask operand, can be thought of as causing the
-//   corresponding bits in the other operand to flip to the opposite value.
-// - 0s cause no change.
-//
-//                            The 0s in our bitmask preserve these values
-// -XOR op- ---expanded---    in the output.
-//            _______________/
-//           /       /
-//   1100   1   1   0   0
-// ^ 0101   0   1   0   1 (bitmask)
-// ------   -   -   -   -
-// = 1001   1   0   0   1 <- This bit was already cleared.
-//              \_______\
-//                       \
-//                         We can think of these bits having flipped
-//                         because of the presence of 1s in those columns
-//                         of our bitmask.
-//
-// Now let's take a look at setting bits with the | operator.
-//
-//
-//
-//
-//
-// ------------------------------------------------------------------------
-// Setting bits with OR:
-// ------------------------------------------------------------------------
-// We can set bits on PORTB with the | (OR) operator, like so:
-//
-// var PORTB: u4 = 0b1001;
-// PORTB = PORTB | 0b0010;
-// print("PORTB: {b:0>4}\n", .{PORTB}); // output: 1011
-//
-// -OR op-  ---expanded---
-//                    _ Set only this bit.
-//                   /
-//   1001   1   0   0   1
-// | 0010   0   0   1   0 (bitmask)
-// ------   -   -   -   -
-// = 1011   1   0   1   1
-//           \___\_______\
-//                        \
-//                          These bits remain untouched because OR-ing with
-//                          a 0 effects no change.
-//
-// ------------------------------------------------------------------------
-// To create a bitmask like 0b0010 used above:
-//
-// 1. First, shift the value 1 over one place with the bitwise << (shift
-// left) operator as indicated below:
-//           1 << 0 -> 0001
-//           1 << 1 -> 0010  <-- Shift 1 one place to the left
-//           1 << 2 -> 0100
-//           1 << 3 -> 1000
-//
-// This allows us to rewrite the above code like this:
-//
-// var PORTB: u4 = 0b1001;
-// PORTB = PORTB | (1 << 1);
-// print("PORTB: {b:0>4}\n", .{PORTB}); // output: 1011
-//
-// Finally, as in the C language, Zig allows us to use the |= operator, so
-// we can rewrite our code again in an even more compact and idiomatic
-// form: PORTB |= (1 << 1)
-
-// So now we've covered how to toggle and set bits. What about clearing
-// them? Well, this is where Zig throws us a curve ball. Don't worry we'll
-// go through it step by step.
-//
-//
-//
-//
-//
-// ------------------------------------------------------------------------
-// Clearing bits with AND and NOT:
-// ------------------------------------------------------------------------
-// We can clear bits with the & (AND) bitwise operator, like so:
-
-// PORTB = 0b1110; // reset PORTB
-// PORTB = PORTB & 0b1011;
-// print("PORTB: {b:0>4}\n", .{PORTB}); // output -> 1010
-//
-// - 0s clear bits when used in conjunction with a bitwise AND.
-// - 1s do nothing, thus preserving the original bits.
-//
-// -AND op- ---expanded---
-//                __________ Clear only this bit.
-//               /
-//   1110   1   1   1   0
-// & 1011   1   0   1   1 (bitmask)
-// ------   -   -   -   -
-// = 1010   1   0   1   0 <- This bit was already cleared.
-//           \_______\
-//                    \
-//                      These bits remain untouched because AND-ing with a
-//                      1 preserves the original bit value whether 0 or 1.
-//
-// ------------------------------------------------------------------------
-// We can use the ~ (NOT) operator to easily create a bitmask like 1011:
-//
-//  1. First, shift the value 1 over two places with the bit-wise << (shift
-//     left) operator as indicated below:
-//          1 << 0 -> 0001
-//          1 << 1 -> 0010
-//          1 << 2 -> 0100 <- The 1 has been shifted two places to the left
-//          1 << 3 -> 1000
-//
-//  2. The second step in creating our bitmask is to invert the bits
-//          ~0100 -> 1011
-//     in C we would write this as:
-//          ~(1 << 2) -> 1011
-//
-//     But if we try to compile ~(1 << 2) in Zig, we'll get an error:
-//          unable to perform binary not operation on type 'comptime_int'
-//
-//     Before Zig can invert our bits, it needs to know the number of
-//     bits it's being asked to invert.
-//
-//     We do this with the @as (cast as) built-in like this:
-//          @as(u4, 1 << 2) -> 0100
-//
-//     Finally, we can invert our new mask by placing the NOT ~ operator
-//     before our expression, like this:
-//          ~@as(u4, 1 << 2) -> 1011
-//
-//     If you are offput by the fact that you can't simply invert bits like
-//     you can in languages such as C without casting to a particular size
-//     of integer, you're not alone. However, this is actually another
-//     instance where Zig is really helpful because it protects you from
-//     difficult to debug integer overflow bugs that can have you tearing
-//     your hair out. In the interest of keeping things sane, Zig requires
-//     you simply to tell it the size of number you are inverting. In the
-//     words of Andrew Kelley, "If you want to invert the bits of an
-//     integer, zig has to know how many bits there are."
-//
-//     For more insight into the Zig team's position on why the language
-//     takes the approach it does with the ~ operator, take a look at
-//     Andrew's comments on the following github issue:
-//     https://github.com/ziglang/zig/issues/1382#issuecomment-414459529
-//
-// Whew, so after all that what we end up with is:
-//          PORTB = PORTB & ~@as(u4, 1 << 2);
-//
-// We can shorten this with the &= combined AND and assignment operator,
-// which applies the AND operator on PORTB and then reassigns PORTB. Here's
-// what that looks like:
-//          PORTB &= ~@as(u4, 1 << 2);
-//
-
-// ------------------------------------------------------------------------
-// Conclusion
-// ------------------------------------------------------------------------
-//
-// While the examples in this quiz have used only 4-bit wide variables,
-// working with 8 bits is no different. Here's an example where we set
-// every other bit beginning with the two's place:
-
-// var PORTD: u8 = 0b0000_0000;
-// print("PORTD: {b:0>8}\n", .{PORTD});
-// PORTD |= (1 << 1);
-// PORTD = setBit(u8, PORTD, 3);
-// PORTD |= (1 << 5) | (1 << 7);
-// print("PORTD: {b:0>8} // set every other bit\n", .{PORTD});
-// PORTD = ~PORTD;
-// print("PORTD: {b:0>8} // bits flipped with NOT (~)\n", .{PORTD});
-// newline();
-//
-// // Here we clear every other bit beginning with the two's place.
-//
-// PORTD = 0b1111_1111;
-// print("PORTD: {b:0>8}\n", .{PORTD});
-// PORTD &= ~@as(u8, 1 << 1);
-// PORTD = clearBit(u8, PORTD, 3);
-// PORTD &= ~@as(u8, (1 << 5) | (1 << 7));
-// print("PORTD: {b:0>8} // clear every other bit\n", .{PORTD});
-// PORTD = ~PORTD;
-// print("PORTD: {b:0>8} // bits flipped with NOT (~)\n", .{PORTD});
-// newline();
-
-// ----------------------------------------------------------------------------
-// Here are some helper functions for manipulating bits
-// ----------------------------------------------------------------------------
-
-// Functions for setting, clearing, and toggling a single bit
-fn setBit(comptime T: type, byte: T, comptime bit_pos: T) !T {
-    return byte | (1 << bit_pos);
-}
-
-test "setBit" {
-    try testing.expectEqual(setBit(u8, 0b0000_0000, 3), 0b0000_1000);
-}
-
-fn clearBit(comptime T: type, byte: T, comptime bit_pos: T) T {
-    return byte & ~@as(T, (1 << bit_pos));
-}
-
-test "clearBit" {
-    try testing.expectEqual(clearBit(u8, 0b1111_1111, 0), 0b1111_1110);
-}
-
-fn toggleBit(comptime T: type, byte: T, comptime bit_pos: T) T {
-    return byte ^ (1 << bit_pos);
-}
-
-test "toggleBit" {
-    var byte = toggleBit(u8, 0b0000_0000, 0);
-    try testing.expectEqual(byte, 0b0000_0001);
-    byte = toggleBit(u8, byte, 0);
-    try testing.expectEqual(byte, 0b0000_0000);
-}
-
-// ----------------------------------------------------------------------------
-// Some additional functions for setting, clearing, and toggling multiple bits
-// at once with a tuple because, hey, why not?
-// ----------------------------------------------------------------------------
-//
-
-fn createBitmask(comptime T: type, comptime bits: anytype) !T {
-    comptime var bitmask: T = 0;
-    inline for (bits) |bit| {
-        if (bit >= @bitSizeOf(T)) return error.BitPosTooLarge;
-        if (bit < 0) return error.BitPosTooSmall;
-
-        bitmask |= (1 << bit);
-    }
-    return bitmask;
-}
-
-test "creating bitmasks from a tuple" {
-    try testing.expectEqual(createBitmask(u8, .{0}), 0b0000_0001);
-    try testing.expectEqual(createBitmask(u8, .{1}), 0b0000_0010);
-    try testing.expectEqual(createBitmask(u8, .{2}), 0b0000_0100);
-    try testing.expectEqual(createBitmask(u8, .{3}), 0b0000_1000);
-    //
-    try testing.expectEqual(createBitmask(u8, .{ 0, 4 }), 0b0001_0001);
-    try testing.expectEqual(createBitmask(u8, .{ 1, 5 }), 0b0010_0010);
-    try testing.expectEqual(createBitmask(u8, .{ 2, 6 }), 0b0100_0100);
-    try testing.expectEqual(createBitmask(u8, .{ 3, 7 }), 0b1000_1000);
-
-    try testing.expectError(error.BitPosTooLarge, createBitmask(u4, .{4}));
-}
-
-fn setBits(byte: u8, bits: anytype) !u8 {
-    const bitmask = try createBitmask(u8, bits);
-    return byte | bitmask;
-}
-
-test "setBits" {
-    try testing.expectEqual(setBits(0b0000_0000, .{0}), 0b0000_0001);
-    try testing.expectEqual(setBits(0b0000_0000, .{7}), 0b1000_0000);
-
-    try testing.expectEqual(setBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111);
-    try testing.expectEqual(setBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111);
-
-    try testing.expectEqual(setBits(0b0000_0000, .{ 2, 3, 4, 5 }), 0b0011_1100);
-
-    try testing.expectError(error.BitPosTooLarge, setBits(0b1111_1111, .{8}));
-    try testing.expectError(error.BitPosTooSmall, setBits(0b1111_1111, .{-1}));
-}
-
-fn clearBits(comptime byte: u8, comptime bits: anytype) !u8 {
-    const bitmask: u8 = try createBitmask(u8, bits);
-    return byte & ~@as(u8, bitmask);
-}
-
-test "clearBits" {
-    try testing.expectEqual(clearBits(0b1111_1111, .{0}), 0b1111_1110);
-    try testing.expectEqual(clearBits(0b1111_1111, .{7}), 0b0111_1111);
-
-    try testing.expectEqual(clearBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000);
-    try testing.expectEqual(clearBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000);
-
-    try testing.expectEqual(clearBits(0b1111_1111, .{ 0, 1, 6, 7 }), 0b0011_1100);
-
-    try testing.expectError(error.BitPosTooLarge, clearBits(0b1111_1111, .{8}));
-    try testing.expectError(error.BitPosTooSmall, clearBits(0b1111_1111, .{-1}));
-}
-
-fn toggleBits(comptime byte: u8, comptime bits: anytype) !u8 {
-    const bitmask = try createBitmask(u8, bits);
-    return byte ^ bitmask;
-}
-
-test "toggleBits" {
-    try testing.expectEqual(toggleBits(0b0000_0000, .{0}), 0b0000_0001);
-    try testing.expectEqual(toggleBits(0b0000_0000, .{7}), 0b1000_0000);
-
-    try testing.expectEqual(toggleBits(0b1111_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b000_0000);
-    try testing.expectEqual(toggleBits(0b0000_0000, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_1111);
-
-    try testing.expectEqual(toggleBits(0b0000_1111, .{ 0, 1, 2, 3, 4, 5, 6, 7 }), 0b1111_0000);
-    try testing.expectEqual(toggleBits(0b0000_1111, .{ 0, 1, 2, 3 }), 0b0000_0000);
-
-    try testing.expectEqual(toggleBits(0b0000_0000, .{ 0, 2, 4, 6 }), 0b0101_0101);
-
-    try testing.expectError(error.BitPosTooLarge, toggleBits(0b1111_1111, .{8}));
-    try testing.expectError(error.BitPosTooSmall, toggleBits(0b1111_1111, .{-1}));
-}
-
-// ----------------------------------------------------------------------------
-// Utility functions
-// ----------------------------------------------------------------------------
-
-fn newline() void {
-    print("\n", .{});
-}
-
-fn checkAnswer(expected: u4, answer: u4) void {
-    if (expected != answer) {
-        print("*************************************************************\n", .{});
-        print("= {b:0>4} <- INCORRECT! THE EXPECTED OUTPUT IS {b:0>4}\n", .{ answer, expected });
-        print("*************************************************************\n", .{});
-    } else {
-        print("= {b:0>4}", .{answer});
-    }
-    newline();
-}