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Diffstat (limited to 'exercises/097_bit_manipulation.zig')
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diff --git a/exercises/097_bit_manipulation.zig b/exercises/097_bit_manipulation.zig deleted file mode 100644 index 0e64ad7..0000000 --- a/exercises/097_bit_manipulation.zig +++ /dev/null @@ -1,95 +0,0 @@ -// -// Bit manipulation is a very powerful tool, 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. -// -// At first glance, it is often not easy to understand what exactly these -// algorithms do when only "numbers" in memory areas change outwardly. -// However, it should 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 -// "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 { - - // Let us use 1101 and 1011 as values for x and y - var x: u8 = 0b1101; - var y: u8 = 0b1011; - - // 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 = {b}; y = {b}\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. |