diff options
Diffstat (limited to 'exercises')
| -rw-r--r-- | exercises/046_optionals2.zig | 2 | ||||
| -rw-r--r-- | exercises/058_quiz7.zig | 2 | ||||
| -rw-r--r-- | exercises/060_floats.zig | 8 | ||||
| -rw-r--r-- | exercises/065_builtins2.zig | 20 | ||||
| -rw-r--r-- | exercises/099_formatting.zig | 2 | ||||
| -rw-r--r-- | exercises/100_for4.zig | 4 | ||||
| -rw-r--r-- | exercises/105_threading2.zig | 2 | ||||
| -rw-r--r-- | exercises/106_files.zig | 2 | ||||
| -rw-r--r-- | exercises/107_files2.zig | 2 | ||||
| -rw-r--r-- | exercises/108_labeled_switch.zig | 20 | ||||
| -rw-r--r-- | exercises/109_vectors.zig | 147 | ||||
| -rw-r--r-- | exercises/110_quiz9.zig | 484 |
12 files changed, 665 insertions, 30 deletions
diff --git a/exercises/046_optionals2.zig b/exercises/046_optionals2.zig index a5436d9..b5fffbb 100644 --- a/exercises/046_optionals2.zig +++ b/exercises/046_optionals2.zig @@ -48,7 +48,7 @@ pub fn main() void { // If e1 and e2 are valid pointers to elephants, // this function links the elephants so that e1's tail "points" to e2. fn linkElephants(e1: ?*Elephant, e2: ?*Elephant) void { - e1.?.*.tail = e2.?; + e1.?.tail = e2.?; } // This function visits all elephants once, starting with the diff --git a/exercises/058_quiz7.zig b/exercises/058_quiz7.zig index cf32fc3..fda83fc 100644 --- a/exercises/058_quiz7.zig +++ b/exercises/058_quiz7.zig @@ -190,7 +190,7 @@ const TripItem = union(enum) { fn printMe(self: TripItem) void { switch (self) { // Oops! The hermit forgot how to capture the union values - // in a switch statement. Please capture both values as + // in a switch statement. Please capture each value as // 'p' so the print statements work! .place => print("{s}", .{p.name}), .path => print("--{}->", .{p.dist}), diff --git a/exercises/060_floats.zig b/exercises/060_floats.zig index 6f341ad..b570518 100644 --- a/exercises/060_floats.zig +++ b/exercises/060_floats.zig @@ -41,14 +41,14 @@ pub fn main() void { // The approximate weight of the Space Shuttle upon liftoff // (including boosters and fuel tank) was 4,480,000 lb. // - // We'll convert this weight from pound to kilograms at a - // conversion of 0.453592kg to the pound. - const shuttle_weight: f16 = 0.453592 * 4480e6; + // We'll convert this weight from pounds to metric units at a + // conversion of 0.453592 kg to the pound. + const shuttle_weight: f16 = 0.453592 * 4480e3; // By default, float values are formatted in scientific // notation. Try experimenting with '{d}' and '{d:.3}' to see // how decimal formatting works. - print("Shuttle liftoff weight: {d:.0}kg\n", .{shuttle_weight}); + print("Shuttle liftoff weight: {d:.0} metric tons\n", .{shuttle_weight}); } // Floating further: diff --git a/exercises/065_builtins2.zig b/exercises/065_builtins2.zig index 0790db4..6b8168c 100644 --- a/exercises/065_builtins2.zig +++ b/exercises/065_builtins2.zig @@ -110,15 +110,15 @@ pub fn main() void { // name will not be printed if the field is of type 'void' // (which is a zero-bit type that takes up no space at all!): if (fields[0].??? != void) { - print(" {s}", .{@typeInfo(Narcissus).@"struct".fields[0].name}); + print(" {s}", .{fields[0].name}); } if (fields[1].??? != void) { - print(" {s}", .{@typeInfo(Narcissus).@"struct".fields[1].name}); + print(" {s}", .{fields[1].name}); } if (fields[2].??? != void) { - print(" {s}", .{@typeInfo(Narcissus).@"struct".fields[2].name}); + print(" {s}", .{fields[2].name}); } // Yuck, look at all that repeated code above! I don't know @@ -136,14 +136,16 @@ pub fn main() void { // But a change after Zig 0.10.0 added the source file name to the // type. "Narcissus" became "065_builtins2.Narcissus". // -// To fix this, I've added this function to strip the filename from -// the front of the type name in the dumbest way possible. (It returns -// a slice of the type name starting at character 14 (assuming -// single-byte characters). +// To fix this, we've added this function to strip the filename from +// the front of the type name. (It returns a slice of the type name +// starting at the index + 1 of character ".") // // We'll be seeing @typeName again in Exercise 070. For now, you can // see that it takes a Type and returns a u8 "string". fn maximumNarcissism(myType: anytype) []const u8 { - // Turn '065_builtins2.Narcissus' into 'Narcissus' - return @typeName(myType)[14..]; + const indexOf = @import("std").mem.indexOf; + + // Turn "065_builtins2.Narcissus" into "Narcissus" + const name = @typeName(myType); + return name[indexOf(u8, name, ".").? + 1 ..]; } diff --git a/exercises/099_formatting.zig b/exercises/099_formatting.zig index 4b64209..37fab45 100644 --- a/exercises/099_formatting.zig +++ b/exercises/099_formatting.zig @@ -16,7 +16,7 @@ // Therefore, the comments for the format() function are the only // way to definitively learn how to format strings in Zig: // -// https://github.com/ziglang/zig/blob/master/lib/std/fmt.zig#L29 +// https://github.com/ziglang/zig/blob/master/lib/std/fmt.zig#L33 // // Zig already has a very nice selection of formatting options. // These can be used in different ways, but generally to convert diff --git a/exercises/100_for4.zig b/exercises/100_for4.zig index e0fa602..c8a1161 100644 --- a/exercises/100_for4.zig +++ b/exercises/100_for4.zig @@ -41,12 +41,12 @@ pub fn main() void { for (hex_nums, ???) |hn, ???| { if (hn != dn) { - std.debug.print("Uh oh! Found a mismatch: {d} vs {d}\n", .{ hn, dn }); + print("Uh oh! Found a mismatch: {d} vs {d}\n", .{ hn, dn }); return; } } - std.debug.print("Arrays match!\n", .{}); + print("Arrays match!\n", .{}); } // // You are perhaps wondering what happens if one of the two lists diff --git a/exercises/105_threading2.zig b/exercises/105_threading2.zig index 7ca8f5c..7e16a1c 100644 --- a/exercises/105_threading2.zig +++ b/exercises/105_threading2.zig @@ -39,7 +39,7 @@ // in practice. Because either you don't need the precision, or you use a // calculator in which the number is stored as a very precise constant. // But at some point this constant was calculated and we are doing the same -// now.The question at this point is, how many partial values do we have +// now. The question at this point is, how many partial values do we have // to calculate for which accuracy? // // The answer is chewing, to get 8 digits after the decimal point we need diff --git a/exercises/106_files.zig b/exercises/106_files.zig index f5fd1ac..b224508 100644 --- a/exercises/106_files.zig +++ b/exercises/106_files.zig @@ -9,7 +9,7 @@ // by organizing them into directories, which hold files and other directories, // thus creating a tree structure that can be navigated. // -// Fortunately, the Zig standard library provides a simple API for interacting +// Fortunately, the Zig Standard Library provides a simple API for interacting // with the file system, see the detail documentation here: // // https://ziglang.org/documentation/master/std/#std.fs diff --git a/exercises/107_files2.zig b/exercises/107_files2.zig index 45e12f5..6768898 100644 --- a/exercises/107_files2.zig +++ b/exercises/107_files2.zig @@ -40,7 +40,7 @@ pub fn main() !void { // okay, seems like a threat of violence is not the answer in this case // can you go here to find a way to read the content? // https://ziglang.org/documentation/master/std/#std.fs.File - // hint: you might find two answers that are both vaild in this case + // hint: you might find two answers that are both valid in this case const bytes_read = zig_read_the_file_or_i_will_fight_you(&content); // Woah, too screamy. I know you're excited for zigling time but tone it down a bit. diff --git a/exercises/108_labeled_switch.zig b/exercises/108_labeled_switch.zig index 88cb196..16a5879 100644 --- a/exercises/108_labeled_switch.zig +++ b/exercises/108_labeled_switch.zig @@ -15,11 +15,11 @@ // 1 => { op = 2; continue; }, // 2 => { op = 3; continue; }, // 3 => return, -// 4 => {}, +// else => {}, // } // break; // } -// std.debug.print("This statement cannot be reached"); +// std.debug.print("This statement cannot be reached\n", .{}); // } // // By combining all we've learned so far, we can now proceed with a labeled switch @@ -34,21 +34,23 @@ // 1 => continue :foo 2, // 2 => continue :foo 3, // 3 => return, -// 4 => {}, +// else => {}, // } -// std.debug.print("This statement cannot be reached"); +// std.debug.print("This statement cannot be reached\n", .{}); // } // // The flow of execution on this second case is: // 1. The switch starts with value '1'; // 2. The switch evaluates to case '1' which in turn uses the continue statement -// to re-evaluate the labeled switch again, now providing the value '2'; +// to re-evaluate the labeled switch again, now providing the value '2'; // 3. In the case '2' we repeat the same pattern as case '1' -// but instead the value to be evaluated is now '3'; -// 4. Finally we get to case '3', where we return from the function as a whole. +// but instead the value to be evaluated is now '3'; +// 4. Finally we get to case '3', where we return from the function as a whole, +// so the debug statement is never executed. +// 5. In this example, since the input does not have clear, exhaustive patterns and +// can essentially be any 'u8' integer, we need to handle all cases not explicitly +// covered by using the 'else => {}' branch as the default case. // -// Since step 4 or a break stament do not exist in this switch, the debug statement is -// never executed // const std = @import("std"); diff --git a/exercises/109_vectors.zig b/exercises/109_vectors.zig new file mode 100644 index 0000000..96892ca --- /dev/null +++ b/exercises/109_vectors.zig @@ -0,0 +1,147 @@ +// So far in Ziglings, we've seen how for loops can be used to +// repeat calculations across an array in several ways. +// +// For loops are generally great for this kind of task, but +// sometimes they don't fully utilize the capabilities of the +// CPU. +// +// Most modern CPUs can execute instructions in which SEVERAL +// calculations are performed WITHIN registers at the SAME TIME. +// These are known as "single instruction, multiple data" (SIMD) +// instructions. SIMD instructions can make code significantly +// more performant. +// +// To see why, imagine we have a program in which we take the +// square root of four (changing) f32 floats. +// +// A simple compiler would take the program and produce machine code +// which calculates each square root sequentially. Most registers on +// modern CPUs have 64 bits, so we could imagine that each float moves +// into a 64-bit register, and the following happens four times: +// +// 32 bits 32 bits +// +-------------------+ +// register | 0 | x | +// +-------------------+ +// +// | +// [SQRT instruction] +// V +// +// +-------------------+ +// | 0 | sqrt(x) | +// +-------------------+ +// +// Notice that half of the register contains blank data to which +// nothing happened. What a waste! What if we were able to use +// that space instead? This is the idea at the core of SIMD. +// +// Most modern CPUs contain specialized registers with at least 128 bits +// for performing SIMD instructions. On a machine with 128-bit SIMD +// registers, a smart compiler would probably NOT issue four sqrt +// instructions as above, but instead pack the floats into a single +// 128-bit register, then execute a single "packed" sqrt +// instruction to do ALL the square root calculations at once. +// +// For example: +// +// +// 32 bits 32 bits 32 bits 32 bits +// +---------------------------------------+ +// register | 4.0 | 9.0 | 25.0 | 49.0 | +// +---------------------------------------+ +// +// | +// [SIMD SQRT instruction] +// V +// +// +---------------------------------------+ +// register | 2.0 | 3.0 | 5.0 | 7.0 | +// +---------------------------------------+ +// +// Pretty cool, right? +// +// Code with SIMD instructions is usually more performant than code +// without SIMD instructions. Zig cares a lot about performance, +// so it has built-in support for SIMD! It has a data structure that +// directly supports SIMD instructions: +// +// +-----------+ +// | Vectors | +// +-----------+ +// +// Operations performed on vectors in Zig will be done in parallel using +// SIMD instructions, whenever possible. +// +// Defining vectors in Zig is straightforwards. No library import is needed. +const v1 = @Vector(3, i32){ 1, 10, 100 }; +const v2 = @Vector(3, f32){ 2.0, 3.0, 5.0 }; + +// Vectors support the same builtin operators as their underlying base types. +const v3 = v1 + v1; // { 2, 20, 200}; +const v4 = v2 * v2; // { 4.0, 9.0, 25.0}; + +// Intrinsics that apply to base types usually extend to vectors. +const v5: @Vector(3, f32) = @floatFromInt(v3); // { 2.0, 20.0, 200.0} +const v6 = v4 - v5; // { 2.0, -11.0, -175.0} +const v7 = @abs(v6); // { 2.0, 11.0, 175.0} + +// We can make constant vectors, and reduce vectors. +const v8: @Vector(4, u8) = @splat(2); // { 2, 2, 2, 2} +const v8_sum = @reduce(.Add, v8); // 8 +const v8_min = @reduce(.Min, v8); // 2 + +// Fixed-length arrays can be automatically assigned to vectors (and vice-versa). +const single_digit_primes = [4]i8{ 2, 3, 5, 7 }; +const prime_vector: @Vector(4, i8) = single_digit_primes; + +// Now let's use vectors to simplify and optimize some code! +// +// Ewa is writing a program in which they frequently want to compare +// two lists of four f32s. Ewa expects the lists to be similar, and +// wants to determine the largest pairwise difference between the lists. +// +// Ewa wrote the following function to figure this out. + +fn calcMaxPairwiseDiffOld(list1: [4]f32, list2: [4]f32) f32 { + var max_diff: f32 = 0; + for (list1, list2) |n1, n2| { + const abs_diff = @abs(n1 - n2); + if (abs_diff > max_diff) { + max_diff = abs_diff; + } + } + return max_diff; +} + +// Ewa heard about vectors in Zig, and started writing a new vector +// version of the function, but has got stuck! +// +// Help Ewa finish the vector version! The examples above should help. + +const Vec4 = @Vector(4, f32); +fn calcMaxPairwiseDiffNew(a: Vec4, b: Vec4) f32 { + const abs_diff_vec = ???; + const max_diff = @reduce(???, abs_diff_vec); + return max_diff; +} + +// Quite the simplification! We could even write the function in one line +// and it would still be readable. +// +// Since the entire function is now expressed in terms of vector operations, +// the Zig compiler will easily be able to compile it down to machine code +// which utilizes the all-powerful SIMD instructions and does a lot of the +// computation in parallel. + +const std = @import("std"); +const print = std.debug.print; + +pub fn main() void { + const l1 = [4]f32{ 3.141, 2.718, 0.577, 1.000 }; + const l2 = [4]f32{ 3.154, 2.707, 0.591, 0.993 }; + const mpd_old = calcMaxPairwiseDiffOld(l1, l2); + const mpd_new = calcMaxPairwiseDiffNew(l1, l2); + print("Max difference (old fn): {d: >5.3}\n", .{mpd_old}); + print("Max difference (new fn): {d: >5.3}\n", .{mpd_new}); +} diff --git a/exercises/110_quiz9.zig b/exercises/110_quiz9.zig new file mode 100644 index 0000000..cd0048b --- /dev/null +++ b/exercises/110_quiz9.zig @@ -0,0 +1,484 @@ +// ---------------------------------------------------------------------------- +// 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 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. +// _______________/ +// / / +// 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 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 (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(); +} |