diff options
| -rw-r--r-- | build.zig | 4 | ||||
| -rw-r--r-- | exercises/097_bit_manipulation.zig | 94 | ||||
| -rw-r--r-- | patches/patches/097_bit_manipulation.patch | 4 |
3 files changed, 102 insertions, 0 deletions
@@ -505,6 +505,10 @@ const exercises = [_]Exercise{ .output = "Running Average: 0.30 0.25 0.20 0.18 0.22", }, .{ + .main_file = "097_bit_manipulation.zig", + .output = "x = 0; y = 1", + }, + .{ .main_file = "999_the_end.zig", .output = "\nThis is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.", }, diff --git a/exercises/097_bit_manipulation.zig b/exercises/097_bit_manipulation.zig new file mode 100644 index 0000000..3b8791b --- /dev/null +++ b/exercises/097_bit_manipulation.zig @@ -0,0 +1,94 @@ +// Bit manipulations is a very powerful tool just also from Zig. +// Since the dawn of the computer age, numerous algorithms have been +// developed that solve tasks solely by moving, setting, or logically +// combining bits. +// +// Zig also uses direct bit manipulation in its standard library for +// functions where possible. And it is often possible with calculations +// based on integers. +// +// Often it is not easy to understand at first glance what exactly these +// algorithms do when only "numbers" in memory areas change outwardly. +// But it must never be forgotten that the numbers only represent the +// interpretation of the bit sequences. +// +// Quasi the reversed case we have otherwise, namely that we represent +// numbers in bit sequences. +// +// We remember: 1 byte = 8 bits = 11111111 = 255 decimal = FF hex. +// +// Zig provides all the necessary functions to change the bits inside +// a variable. It is distinguished whether the bit change leads to an +// overflow or not.The details are in the Zig documentation in section +// 10.1 "Table of Operators". +// +// Here are some examples of how the bits of variables can be changed: +// +// const numOne: u8 = 15; // = 0000 1111 +// const numTwo: u8 = 245; // = 1111 0101 +// +// const res1 = numOne >> 4; // = 0000 0000 - shift right +// const res2 = numOne << 4; // = 1111 0000 - shift left +// const res3 = numOne & numTwo; // = 0000 0101 - and +// const res4 = numOne | numTwo; // = 1111 1111 - or +// const res5 = numOne ^ numTwo; // = 1111 1010 - xor +// +// +// To familiarize ourselves with bit manipulation, we start with a simple +// but often underestimated function and then add other exercises in +// loose order. +// +// The following text contains excerpts from Wikipedia. +// +// Swap +// In computer programming, the act of swapping two variables refers to +// mutually exchanging the values of the variables. Usually, this is +// done with the data in memory. For example, in a program, two variables +// may be defined thus (in pseudocode): +// +// data_item x := 1 +// data_item y := 0 +// +// swap (x, y); +// +// After swap() is performed, x will contain the value 0 and y will +// contain 1; their values have been exchanged. The simplest and probably +// most widely used method to swap two variables is to use a third temporary +// variable: +// +// define swap (x, y) +// temp := x +// x := y +// y := temp +// +// However, with integers we can also achieve the swap function simply by +// bit manipulation. To do this, the variables are mutually linked with xor +// and the result is the same. + +const std = @import("std"); +const print = std.debug.print; + +pub fn main() !void { + + // As in the example above, we use 1 and 0 as values for x and y + var x: u8 = 1; + var y: u8 = 0; + + // Now we swap the values of the two variables by doing xor on them + x ^= y; + y ^= x; + + // What must be written here? + ???; + + print("x = {d}; y = {d}\n", .{ x, y }); +} + +// This variable swap takes advantage of the fact that the value resulting +// from the xor of two values contains both of these values. +// This circumstance was (and still is) sometimes used for encryption. +// Value XOR Key = Crypto. => Crypto XOR Key = Value. +// Since this can be swapped arbitrarily, you can swap two variables in this way. +// +// For Crypto it is better not to use this, but in sorting algorithms like +// Bubble Sort it works very well. diff --git a/patches/patches/097_bit_manipulation.patch b/patches/patches/097_bit_manipulation.patch new file mode 100644 index 0000000..e216309 --- /dev/null +++ b/patches/patches/097_bit_manipulation.patch @@ -0,0 +1,4 @@ +82c82 +< ???; +--- +> x ^= y; |