12

Builtin Operators

Taiki Mineno edited this page 2019-07-14 16:23:03 +09:00

Table of Contents

• List of operators

List of 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.

Prev (Combinational Circuits) Next (Width Inference)