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diff --git a/exercises/110_bit_manipulation3.zig b/exercises/110_bit_manipulation3.zig deleted file mode 100644 index 4ac2032..0000000 --- a/exercises/110_bit_manipulation3.zig +++ /dev/null @@ -1,454 +0,0 @@ -// ---------------------------------------------------------------------------- -// 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? This exercise is designed to -// give you a taste of what it's like to control registers in a -// microcontroller. Let's get started! -// -// 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. In this -// exercise, we'll take a closer look at bit manipulation and how we can write -// code that sets and clears specific bits as we would if we were programming -// the pins on a real microcontroller. Included at the end of this exercise 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 exercise in bit manipulation. It should be noted that -// in the following examples 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 examples 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 - // - // Let's first take a look at toggling bits. - // - // ------------------------------------------------------------------------ - // 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 outputing 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. - // _______________/ - // / / - // 0110 1 1 0 0 - // ^ 1111 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. - - 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(); - - // 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 (bit mask) - // ------ - - - - - // = 1011 1 0 1 1 - // \___\_______\ - // \ - // These bits remain untouched because OR-ing with - // a 0 effects no change. - // - // ------------------------------------------------------------------------ - // To create a bit mask 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) - - 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(); - - // 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 conjuction 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 (bit mask) - // ------ - - - - - // = 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 bit mask 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 bit mask 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); - // - - 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(); - - // ------------------------------------------------------------------------ - // Conclusion - // ------------------------------------------------------------------------ - // - // While the examples in this exercise have used only 4-bit wide variables, - // working with 8 bits is no different. Here's a 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(); -} |