Reorganize website docs (#1806)

Updates to chisel3 documentation for website:
* guard code examples with mdoc and fix errors encountered along the way
* move some website content here vs splitting the content across two repos
* Bring in the interval-types and loading memories content so that it will be visible from the website
* remove all references to the wiki (deprecated)
* Remove reference to Wiki from the README
* fix tabbing and compile of chisel3-vs-chisel2 section
* Appendix: faqs now guarded and compile
* FAQs: move to resources section

1 files changed, 65 insertions, 0 deletions

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+---
+layout: docs
+title:  "Operators"
+section: "chisel3"
+---
+
+# Chisel Operators
+
+Chisel defines a set of hardware operators:
+
+| Operation        | Explanation |
+| ---------        | ---------           |
+| **Bitwise operators**                       | **Valid on:** SInt, UInt, Bool    |
+| `val invertedX = ~x`                        | Bitwise NOT |
+| `val hiBits = x & "h_ffff_0000".U`          | Bitwise AND                     |
+| `val flagsOut = flagsIn \| overflow`         | Bitwise OR                      |
+| `val flagsOut = flagsIn ^ toggle`           | Bitwise XOR                     |
+| **Bitwise reductions.**                     | **Valid on:** SInt and UInt. Returns Bool. |
+| `val allSet = x.andR`                       | AND reduction                     |
+| `val anySet = x.orR`                        | OR reduction                      |
+| `val parity = x.xorR`                       | XOR reduction                     |
+| **Equality comparison.**                    | **Valid on:** SInt, UInt, and Bool. Returns Bool. |
+| `val equ = x === y`                         | Equality                          |
+| `val neq = x =/= y`                         | Inequality                        |
+| **Shifts**                                  | **Valid on:** SInt and UInt       |
+| `val twoToTheX = 1.S << x`                  | Logical shift left                |
+| `val hiBits = x >> 16.U`                    | Right shift (logical on UInt and arithmetic on SInt). |
+| **Bitfield manipulation**                   | **Valid on:** SInt, UInt, and Bool. |
+| `val xLSB = x(0)`                           | Extract single bit, LSB has index 0.     |
+| `val xTopNibble = x(15, 12)`                | Extract bit field from end to start bit position.     |
+| `val usDebt = Fill(3, "hA".U)`              | Replicate a bit string multiple times.     |
+| `val float = Cat(sign, exponent, mantissa)` | Concatenates bit fields, with first argument on left.     |
+| **Logical Operations**                      | **Valid on:** Bool
+| `val sleep = !busy`                         | Logical NOT                       |
+| `val hit = tagMatch && valid`               | Logical AND                       |
+| `val stall = src1busy || src2busy`          | Logical OR                        |
+| `val out = Mux(sel, inTrue, inFalse)`       | Two-input mux where sel is a Bool |
+| **Arithmetic operations**                   | **Valid on Nums:** SInt and UInt.  |
+| `val sum = a + b` *or* `val sum = a +% b`   | Addition (without width expansion) |
+| `val sum = a +& b`                          | Addition (with width expansion)    |
+| `val diff = a - b` *or* `val diff = a -% b` | Subtraction (without width expansion) |
+| `val diff = a -& b`                         | Subtraction (with width expansion) |
+| `val prod = a * b`                          | Multiplication                     |
+| `val div = a / b`                           | Division                           |
+| `val mod = a % b`                           | Modulus                            |
+| **Arithmetic comparisons**                  | **Valid on Nums:** SInt and UInt. Returns Bool. |
+| `val gt = a > b`                            | Greater than                       |
+| `val gte = a >= b`                          | Greater than or equal              |
+| `val lt = a < b`                            | Less than                          |
+| `val lte = a <= b`                          | Less than or equal                 |
+
+>Our choice of operator names was constrained by the Scala language.
+We have to use triple equals```===``` for equality and ```=/=```
+for inequality to allow the
+native Scala equals operator to remain usable.
+
+The Chisel operator precedence is not directly defined as part of the Chisel language.
+Practically, it is determined by the evaluation order of the circuit,
+which natuarally follows the [Scala operator precedence](https://docs.scala-lang.org/tour/operators.html).
+If in doubt of operator precedence, use parentheses.
+
+> The Chisel/Scala operator precedence is similar but
+not identical to precedence in Java or C. Verilog has the same operator precedence as C, but VHDL
+does not. Verilog has precedence ordering for logic operations, but in VHDL
+those operators have the same precedence and are evaluated from left to right.