Add Bitwise Operations concept

concepts/bitwise-operations/.meta/config.json

@@ -0,0 +1,7 @@
+{
+  "authors": [
+    "colinleach"
+  ],
+  "contributors": [],
+  "blurb": "Kotlin provides a set of bitwise operations that allow you to manipulate the individual bits of integers."
+}

concepts/bitwise-operations/about.md

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+# About Bits
+
+Binary digits ultimately map directly to the transistors in your CPU or RAM, and whether each is "on" or "off".
+
+Low-level manipulation, informally called "bit-twiddling", is particularly important in system languages.
+
+Higher-level languages like Kotlin usually abstract away most of this detail.
+However, a basic range of bit-level operations [is available][ref-bitwise].
+
+~~~~Exercism/note
+To see human-readable binary output, nearly all the examples below need to be wrapped in an [`Integer.toBinaryString()`][web-binstring] function, or converted with `toString(radix = 2)`.
+
+This is visually distracting, so most occurrences of this function have been edited out, and the results are represented with `0b` notation.
+
+[web-binstring]: https://www.baeldung.com/kotlin/int-binary-representation
+~~~~
+
+## Bit-shift operations
+
+`Int` or `Long` types, signed or unsigned, can be represented as a string of 1's and 0's and manipulated as a sequence of bits.
+
+Perhaps surprisingly, `Byte` or `Short` types are not compatible with most bitwise operations in Kotlin.
+All the examples below use 32-bit integers (`Int` or `UInt`).
+
+```kotlin
+val ns = 0b111  // 7 decimal
+Integer.toBinaryString(ns)  // => "111"
+```
+
+Bit-shifts just move everything to the left or right by a specified number of positions.
+Some bits drop off one end, and the other end is padded with zeros or ones.
+
+- Left shift with `shl`: zero-padding.
+- Right shift with `shr` or `ushr`: zero padding for positive numbers.
+- See below for more on negative signed integers.
+
+```kotlin
+val ns = 0b111  // 7 decimal
+ns shl 1  // => 0b1110, decimal 14
+ns shr 1  // => 0b11, decimal 3
+ns ushr 1  // => 0b11
+
+val nu: UInt = 0b111u  // 7 unsigned
+nu shr 1  //  => 0b11
+```
+
+Each left-shift doubles the value, and each right-shift halves it (subject to truncation).
+This is more obvious in decimal representation:
+
+```kotlin
+3 shl 2  // => 12
+24 shr 3 // => 3
+```
+
+Such bit-shifting is much faster than "proper" arithmetic, making the technique very popular in low-level coding.
+
+With _negative integers_, we need to be a bit more careful.
+
+Negative values are stored in [two's complement][wiki-2complement] form, which means that the left-most bit is 1.
+No problem for a left-shift, but when right-shifting how do we pad the left-most bits?
+
+```kotlin
+val ns = -0b111  // => 0b11111111111111111111111111111001
+
+// shift left: simple
+ns shl 1  // => 0b11111111111111111111111111110010, decimal -14
+
+// shift right: preserves sign bit
+ns shr 1  // => 0b11111111111111111111111111111100, decimal -4
+
+// unsigned shift right: left-pads with zeros
+ns ushr 1 // => 0b01111111111111111111111111111100, decimal 2147483644
+```
+
+The [`shr`][ref-shr] operator performs [arithmetic shift][wiki-arithmetic], preserving the sign bit.
+
+The [`ushr`][ref-ushr] operator performs [logical shift][wiki-logical], padding with zeros as if the number was unsigned.
+
+## Bitwise logic
+
+We saw in the [Booleans Concept][concept-booleans] that the operators `&&` (and), `||` (or) and `!` (not) are used with boolean values.
+
+There are equivalent operators `and`, `or`, `xor` ([exclusive-or][wiki-xor]) to compare the bits in two integers, and an `inv` (inversion) function to flip all the bits.
+
+```kotlin
+0b1011 and 0b0010 //  bit is 1 in both numbers
+// => 0b0010
+
+0b1011 or 0b0010 // bit is 1 in at least one number
+// => 0b1011
+
+0b1011 xor 0b0010 // bit is 1 in exactly one number, not both
+// => 0b1001
+
+0b1011.inv() // flip all bits (in a 32-bit signed Int)
+// => 0b11111111111111111111111111110100
+```
+
+
+[ref-bitwise]: https://kotlinlang.org/docs/numbers.html#bitwise-operations
+[wiki-xor]: https://en.wikipedia.org/wiki/Exclusive_or
+[wiki-2complement]: https://en.wikipedia.org/wiki/Two%27s_complement
+[wiki-arithmetic]: https://en.wikipedia.org/wiki/Arithmetic_shift
+[wiki-logical]: https://en.wikipedia.org/wiki/Logical_shift
+[web-binstring]: https://www.baeldung.com/kotlin/int-binary-representation
+[ref-shr]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/shr.html
+[ref-ushr]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/ushr.html
+[concept-booleans]: https://exercism.org/tracks/kotlin/concepts/booleans

concepts/bitwise-operations/introduction.md

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+# Introduction
+
+Binary digits ultimately map directly to the transistors in your CPU or RAM, and whether each is "on" or "off".
+
+Low-level manipulation, informally called "bit-twiddling", is particularly important in system languages.
+
+Higher-level languages like Kotlin usually abstract away most of this detail.
+However, a basic range of bit-level operations [is available][ref-bitwise].
+
+## Bit-shift operations
+
+`Int` or `Long` types, signed or unsigned, can be represented as a string of 1's and 0's and manipulated as a sequence of bits.
+
+Perhaps surprisingly, `Byte` or `Short` types are not compatible with most bitwise operations in Kotlin.
+All the examples below use 32-bit integers (`Int` or `UInt`).
+
+```kotlin
+val ns = 0b111  // 7 decimal
+Integer.toBinaryString(ns)  // => "111"
+```
+
+Bit-shifts just move everything to the left or right by a specified number of positions.
+Some bits drop off one end, and the other end is padded with zeros or ones.
+
+- Left shift with `shl`: zero-padding.
+- Right shift with `shr` or `ushr`: zero padding for positive numbers.
+- See below for more on negative signed integers.
+
+```kotlin
+val ns = 0b111  // 7 decimal
+ns shl 1  // => 0b1110, decimal 14
+ns shr 1  // => 0b11, decimal 3
+ns ushr 1  // => 0b11
+
+val nu: UInt = 0b111u  // 7 unsigned
+nu shr 1  //  => 0b11
+```
+
+Each left-shift doubles the value, and each right-shift halves it (subject to truncation).
+This is more obvious in decimal representation:
+
+```kotlin
+3 shl 2  // => 12
+24 shr 3 // => 3
+```
+
+Such bit-shifting is much faster than "proper" arithmetic, making the technique very popular in low-level coding.
+
+With _negative integers_, we need to be a bit more careful.
+
+Negative values are stored in [two's complement][wiki-2complement] form, which means that the left-most bit is 1.
+No problem for a left-shift, but when right-shifting how do we pad the left-most bits?
+
+```kotlin
+val ns = -0b111  // => 0b11111111111111111111111111111001
+
+// shift left: simple
+ns shl 1  // => 0b11111111111111111111111111110010, decimal -14
+
+// shift right: preserves sign bit
+ns shr 1  // => 0b11111111111111111111111111111100, decimal -4
+
+// unsigned shift right: left-pads with zeros
+ns ushr 1 // => 0b01111111111111111111111111111100, decimal 2147483644
+```
+
+The `shr` operator performs [arithmetic shift][wiki-arithmetic], preserving the sign bit.
+
+The `ushr` operator performs [logical shift][wiki-logical], padding with zeros as if the number was unsigned.
+
+## Bitwise logic
+
+We saw in the [Booleans Concept][concept-booleans] that the operators `&&` (and), `||` (or) and `!` (not) are used with boolean values.
+
+There are equivalent operators `and`, `or`, `xor` ([exclusive-or][wiki-xor]) to compare the bits in two integers, and an `inv` (inversion) function to flip all the bits.
+
+```kotlin
+0b1011 and 0b0010 //  bit is 1 in both numbers
+// => 0b0010
+
+0b1011 or 0b0010 // bit is 1 in at least one number
+// => 0b1011
+
+0b1011 xor 0b0010 // bit is 1 in exactly one number, not both
+// => 0b1001
+
+0b1011.inv() // flip all bits (in a 32-bit signed Int)
+// => 0b11111111111111111111111111110100
+```
+
+
+[ref-bitwise]: https://kotlinlang.org/docs/numbers.html#bitwise-operations
+[wiki-xor]: https://en.wikipedia.org/wiki/Exclusive_or
+[wiki-2complement]: https://en.wikipedia.org/wiki/Two%27s_complement
+[wiki-arithmetic]: https://en.wikipedia.org/wiki/Arithmetic_shift
+[wiki-logical]: https://en.wikipedia.org/wiki/Logical_shift
+[concept-booleans]: https://exercism.org/tracks/kotlin/concepts/booleans

concepts/bitwise-operations/links.json

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+[
+  {
+    "url": "https://kotlinlang.org/docs/numbers.html#bitwise-operations",
+    "description": "Kotlin manual: bitwise operations"
+  }
+]

config.json

@@ -1387,6 +1387,11 @@
       "uuid": "168827c0-4867-449a-ad22-611c87314c48",
       "slug": "conditionals",
       "name": "Conditionals"
+    },
+    {
+      "uuid": "1050abed-4271-4519-a44c-a0ca121c7de2",
+      "slug": "bitwise-operations",
+      "name": "Bitwise Operations"
     }
   ],
   "key_features": [