From 9036d96bb032c19de31131f2296120e708cbc3dc Mon Sep 17 00:00:00 2001
From: ducky
Date: Thu, 5 May 2016 11:50:39 -0700
Subject: Move Chisel API into separate chiselFrontend compilation unit in
 preparation for source locator macros

---
 chiselFrontend/src/main/scala/Chisel/Bits.scala | 571 ++++++++++++++++++++++++
 1 file changed, 571 insertions(+)
 create mode 100644 chiselFrontend/src/main/scala/Chisel/Bits.scala

(limited to 'chiselFrontend/src/main/scala/Chisel/Bits.scala')

diff --git a/chiselFrontend/src/main/scala/Chisel/Bits.scala b/chiselFrontend/src/main/scala/Chisel/Bits.scala
new file mode 100644
index 00000000..44d9b660
--- /dev/null
+++ b/chiselFrontend/src/main/scala/Chisel/Bits.scala
@@ -0,0 +1,571 @@
+// See LICENSE for license details.
+
+package Chisel
+
+import internal._
+import internal.Builder.pushOp
+import internal.firrtl._
+import firrtl.PrimOp._
+
+/** Element is a leaf data type: it cannot contain other Data objects. Example
+  * uses are for representing primitive data types, like integers and bits.
+  */
+abstract class Element(dirArg: Direction, val width: Width) extends Data(dirArg)
+
+/** A data type for values represented by a single bitvector. Provides basic
+  * bitwise operations.
+  */
+sealed abstract class Bits(dirArg: Direction, width: Width, override val litArg: Option[LitArg])
+    extends Element(dirArg, width) {
+  // TODO: perhaps make this concrete?
+  // Arguments for: self-checking code (can't do arithmetic on bits)
+  // Arguments against: generates down to a FIRRTL UInt anyways
+
+  private[Chisel] def fromInt(x: BigInt): this.type
+
+  private[Chisel] def flatten: IndexedSeq[Bits] = IndexedSeq(this)
+
+  def cloneType: this.type = cloneTypeWidth(width)
+
+  override def <> (that: Data): Unit = this := that
+
+  def tail(n: Int): UInt = {
+    val w = width match {
+      case KnownWidth(x) =>
+        require(x >= n, s"Can't tail($n) for width $x < $n")
+        Width(x - n)
+      case UnknownWidth() => Width()
+    }
+    binop(UInt(width = w), TailOp, n)
+  }
+
+  def head(n: Int): UInt = {
+    width match {
+      case KnownWidth(x) => require(x >= n, s"Can't head($n) for width $x < $n")
+      case UnknownWidth() =>
+    }
+    binop(UInt(width = n), HeadOp, n)
+  }
+
+  /** Returns the specified bit on this wire as a [[Bool]], statically
+    * addressed.
+    */
+  final def apply(x: BigInt): Bool = {
+    if (x < 0) {
+      Builder.error(s"Negative bit indices are illegal (got $x)")
+    }
+    if (isLit()) {
+      Bool(((litValue() >> x.toInt) & 1) == 1)
+    } else {
+      pushOp(DefPrim(Bool(), BitsExtractOp, this.ref, ILit(x), ILit(x)))
+    }
+  }
+
+  /** Returns the specified bit on this wire as a [[Bool]], statically
+    * addressed.
+    *
+    * @note convenience method allowing direct use of Ints without implicits
+    */
+  final def apply(x: Int): Bool =
+    apply(BigInt(x))
+
+  /** Returns the specified bit on this wire as a [[Bool]], dynamically
+    * addressed.
+    */
+  final def apply(x: UInt): Bool =
+    (this >> x)(0)
+
+  /** Returns a subset of bits on this wire from `hi` to `lo` (inclusive),
+    * statically addressed.
+    *
+    * @example
+    * {{{
+    * myBits = 0x5 = 0b101
+    * myBits(1,0) => 0b01  // extracts the two least significant bits
+    * }}}
+    */
+  final def apply(x: Int, y: Int): UInt = {
+    if (x < y || y < 0) {
+      Builder.error(s"Invalid bit range ($x,$y)")
+    }
+    val w = x - y + 1
+    if (isLit()) {
+      UInt((litValue >> y) & ((BigInt(1) << w) - 1), w)
+    } else {
+      pushOp(DefPrim(UInt(width = w), BitsExtractOp, this.ref, ILit(x), ILit(y)))
+    }
+  }
+
+  // REVIEW TODO: again, is this necessary? Or just have this and use implicits?
+  final def apply(x: BigInt, y: BigInt): UInt = apply(x.toInt, y.toInt)
+
+  private[Chisel] def unop[T <: Data](dest: T, op: PrimOp): T =
+    pushOp(DefPrim(dest, op, this.ref))
+  private[Chisel] def binop[T <: Data](dest: T, op: PrimOp, other: BigInt): T =
+    pushOp(DefPrim(dest, op, this.ref, ILit(other)))
+  private[Chisel] def binop[T <: Data](dest: T, op: PrimOp, other: Bits): T =
+    pushOp(DefPrim(dest, op, this.ref, other.ref))
+  private[Chisel] def compop(op: PrimOp, other: Bits): Bool =
+    pushOp(DefPrim(Bool(), op, this.ref, other.ref))
+  private[Chisel] def redop(op: PrimOp): Bool =
+    pushOp(DefPrim(Bool(), op, this.ref))
+
+  /** Returns this wire zero padded up to the specified width.
+    *
+    * @note for SInts only, this does sign extension
+    */
+  def pad (other: Int): this.type = binop(cloneTypeWidth(this.width max Width(other)), PadOp, other)
+
+  /** Shift left operation */
+  // REVIEW TODO: redundant
+  // REVIEW TODO: should these return this.type or Bits?
+  def << (other: BigInt): Bits
+
+  /** Returns this wire statically left shifted by the specified amount,
+    * inserting zeros into the least significant bits.
+    *
+    * The width of the output is `other` larger than the input.
+    */
+  def << (other: Int): Bits
+
+  /** Returns this wire dynamically left shifted by the specified amount,
+    * inserting zeros into the least significant bits.
+    *
+    * The width of the output is `pow(2, width(other))` larger than the input.
+    */
+  def << (other: UInt): Bits
+
+  /** Shift right operation */
+  // REVIEW TODO: redundant
+  def >> (other: BigInt): Bits
+
+  /** Returns this wire statically right shifted by the specified amount,
+    * inserting zeros into the most significant bits.
+    *
+    * The width of the output is the same as the input.
+    */
+  def >> (other: Int): Bits
+
+  /** Returns this wire dynamically right shifted by the specified amount,
+    * inserting zeros into the most significant bits.
+    *
+    * The width of the output is the same as the input.
+    */
+  def >> (other: UInt): Bits
+
+  /** Returns the contents of this wire as a [[Vec]] of [[Bool]]s.
+    */
+  def toBools: Vec[Bool] = Vec.tabulate(this.getWidth)(i => this(i))
+
+  /** Reinterpret cast to a SInt.
+    *
+    * @note value not guaranteed to be preserved: for example, an UInt of width
+    * 3 and value 7 (0b111) would become a SInt with value -1
+    */
+  def asSInt(): SInt
+
+  /** Reinterpret cast to an UInt.
+    *
+    * @note value not guaranteed to be preserved: for example, a SInt of width
+    * 3 and value -1 (0b111) would become an UInt with value 7
+    */
+  def asUInt(): UInt
+
+  /** Reinterpret cast to Bits. */
+  def asBits(): Bits = asUInt
+
+  @deprecated("Use asSInt, which makes the reinterpret cast more explicit", "chisel3")
+  final def toSInt(): SInt = asSInt
+  @deprecated("Use asUInt, which makes the reinterpret cast more explicit", "chisel3")
+  final def toUInt(): UInt = asUInt
+
+  def toBool(): Bool = width match {
+    case KnownWidth(1) => this(0)
+    case _ => throwException(s"can't covert UInt<$width> to Bool")
+  }
+
+  /** Returns this wire concatenated with `other`, where this wire forms the
+    * most significant part and `other` forms the least significant part.
+    *
+    * The width of the output is sum of the inputs.
+    */
+  def ## (other: Bits): UInt = {
+    val w = this.width + other.width
+    pushOp(DefPrim(UInt(w), ConcatOp, this.ref, other.ref))
+  }
+
+  @deprecated("Use asBits, which makes the reinterpret cast more explicit and actually returns Bits", "chisel3")
+  override def toBits: UInt = asUInt
+
+  override def fromBits(n: Bits): this.type = {
+    val res = Wire(this).asInstanceOf[this.type]
+    res := n
+    res
+  }
+}
+
+/** Provides a set of operations to create UInt types and literals.
+  * Identical in functionality to the UInt companion object.
+  */
+object Bits extends UIntFactory
+
+// REVIEW TODO: Further discussion needed on what Num actually is.
+/** Abstract trait defining operations available on numeric-like wire data
+  * types.
+  */
+abstract trait Num[T <: Data] {
+  // def << (b: T): T
+  // def >> (b: T): T
+  //def unary_-(): T
+
+  // REVIEW TODO: double check ops conventions against FIRRTL
+
+  /** Outputs the sum of `this` and `b`. The resulting width is the max of the
+    * operands plus 1 (should not overflow).
+    */
+  def +  (b: T): T
+
+  /** Outputs the product of `this` and `b`. The resulting width is the sum of
+    * the operands.
+    *
+    * @note can generate a single-cycle multiplier, which can result in
+    * significant cycle time and area costs
+    */
+  def *  (b: T): T
+
+  /** Outputs the quotient of `this` and `b`.
+    *
+    * TODO: full rules
+    */
+  def /  (b: T): T
+
+  def %  (b: T): T
+
+  /** Outputs the difference of `this` and `b`. The resulting width is the max
+   *  of the operands plus 1 (should not overflow).
+    */
+  def -  (b: T): T
+
+  /** Outputs true if `this` < `b`.
+    */
+  def <  (b: T): Bool
+
+  /** Outputs true if `this` <= `b`.
+    */
+  def <= (b: T): Bool
+
+  /** Outputs true if `this` > `b`.
+    */
+  def >  (b: T): Bool
+
+  /** Outputs true if `this` >= `b`.
+    */
+  def >= (b: T): Bool
+
+  /** Outputs the minimum of `this` and `b`. The resulting width is the max of
+    * the operands.
+    */
+  def min(b: T): T = Mux(this < b, this.asInstanceOf[T], b)
+
+  /** Outputs the maximum of `this` and `b`. The resulting width is the max of
+    * the operands.
+    */
+  def max(b: T): T = Mux(this < b, b, this.asInstanceOf[T])
+}
+
+/** A data type for unsigned integers, represented as a binary bitvector.
+  * Defines arithmetic operations between other integer types.
+  */
+sealed class UInt private[Chisel] (dir: Direction, width: Width, lit: Option[ULit] = None)
+    extends Bits(dir, width, lit) with Num[UInt] {
+  private[Chisel] override def cloneTypeWidth(w: Width): this.type =
+    new UInt(dir, w).asInstanceOf[this.type]
+  private[Chisel] def toType = s"UInt$width"
+
+  override private[Chisel] def fromInt(value: BigInt): this.type = UInt(value).asInstanceOf[this.type]
+
+  override def := (that: Data): Unit = that match {
+    case _: UInt => this connect that
+    case _ => this badConnect that
+  }
+
+  // TODO: refactor to share documentation with Num or add independent scaladoc
+  def unary_- : UInt = UInt(0) - this
+  def unary_-% : UInt = UInt(0) -% this
+  def +& (other: UInt): UInt = binop(UInt((this.width max other.width) + 1), AddOp, other)
+  def + (other: UInt): UInt = this +% other
+  def +% (other: UInt): UInt = (this +& other) tail 1
+  def -& (other: UInt): UInt = binop(UInt((this.width max other.width) + 1), SubOp, other)
+  def - (other: UInt): UInt = this -% other
+  def -% (other: UInt): UInt = (this -& other) tail 1
+  def * (other: UInt): UInt = binop(UInt(this.width + other.width), TimesOp, other)
+  def * (other: SInt): SInt = other * this
+  def / (other: UInt): UInt = binop(UInt(this.width), DivideOp, other)
+  def % (other: UInt): UInt = binop(UInt(this.width), RemOp, other)
+
+  def & (other: UInt): UInt = binop(UInt(this.width max other.width), BitAndOp, other)
+  def | (other: UInt): UInt = binop(UInt(this.width max other.width), BitOrOp, other)
+  def ^ (other: UInt): UInt = binop(UInt(this.width max other.width), BitXorOp, other)
+
+  /** Returns this wire bitwise-inverted. */
+  def unary_~ : UInt = unop(UInt(width = width), BitNotOp)
+
+  // REVIEW TODO: Can this be defined on Bits?
+  def orR: Bool = this != UInt(0)
+  def andR: Bool = ~this === UInt(0)
+  def xorR: Bool = redop(XorReduceOp)
+
+  def < (other: UInt): Bool = compop(LessOp, other)
+  def > (other: UInt): Bool = compop(GreaterOp, other)
+  def <= (other: UInt): Bool = compop(LessEqOp, other)
+  def >= (other: UInt): Bool = compop(GreaterEqOp, other)
+  def != (other: UInt): Bool = compop(NotEqualOp, other)
+  def =/= (other: UInt): Bool = compop(NotEqualOp, other)
+  def === (other: UInt): Bool = compop(EqualOp, other)
+  def unary_! : Bool = this === Bits(0)
+
+  // REVIEW TODO: Can these also not be defined on Bits?
+  def << (other: Int): UInt = binop(UInt(this.width + other), ShiftLeftOp, other)
+  def << (other: BigInt): UInt = this << other.toInt
+  def << (other: UInt): UInt = binop(UInt(this.width.dynamicShiftLeft(other.width)), DynamicShiftLeftOp, other)
+  def >> (other: Int): UInt = binop(UInt(this.width.shiftRight(other)), ShiftRightOp, other)
+  def >> (other: BigInt): UInt = this >> other.toInt
+  def >> (other: UInt): UInt = binop(UInt(this.width), DynamicShiftRightOp, other)
+
+  def bitSet(off: UInt, dat: Bool): UInt = {
+    val bit = UInt(1, 1) << off
+    Mux(dat, this | bit, ~(~this | bit))
+  }
+
+  def === (that: BitPat): Bool = that === this
+  def != (that: BitPat): Bool = that != this
+  def =/= (that: BitPat): Bool = that =/= this
+
+  /** Returns this UInt as a [[SInt]] with an additional zero in the MSB.
+    */
+  // TODO: this eventually will be renamed as toSInt, once the existing toSInt
+  // completes its deprecation phase.
+  def zext(): SInt = pushOp(DefPrim(SInt(width + 1), ConvertOp, ref))
+
+  /** Returns this UInt as a [[SInt]], without changing width or bit value. The
+    * SInt is not guaranteed to have the same value (for example, if the MSB is
+    * high, it will be interpreted as a negative value).
+    */
+  def asSInt(): SInt = pushOp(DefPrim(SInt(width), AsSIntOp, ref))
+
+  def asUInt(): UInt = this
+}
+
+// This is currently a factory because both Bits and UInt inherit it.
+private[Chisel] sealed trait UIntFactory {
+  /** Create a UInt type with inferred width. */
+  def apply(): UInt = apply(NO_DIR, Width())
+  /** Create a UInt type or port with fixed width. */
+  def apply(dir: Direction = NO_DIR, width: Int): UInt = apply(dir, Width(width))
+  /** Create a UInt port with inferred width. */
+  def apply(dir: Direction): UInt = apply(dir, Width())
+
+  /** Create a UInt literal with inferred width. */
+  def apply(value: BigInt): UInt = apply(value, Width())
+  /** Create a UInt literal with fixed width. */
+  def apply(value: BigInt, width: Int): UInt = apply(value, Width(width))
+  /** Create a UInt literal with inferred width. */
+  def apply(n: String): UInt = apply(parse(n), parsedWidth(n))
+  /** Create a UInt literal with fixed width. */
+  def apply(n: String, width: Int): UInt = apply(parse(n), width)
+
+  /** Create a UInt type with specified width. */
+  def apply(width: Width): UInt = apply(NO_DIR, width)
+  /** Create a UInt port with specified width. */
+  def apply(dir: Direction, width: Width): UInt = new UInt(dir, width)
+  /** Create a UInt literal with specified width. */
+  def apply(value: BigInt, width: Width): UInt = {
+    val lit = ULit(value, width)
+    new UInt(NO_DIR, lit.width, Some(lit))
+  }
+
+  private def parse(n: String) = {
+    val (base, num) = n.splitAt(1)
+    val radix = base match {
+      case "x" | "h" => 16
+      case "d" => 10
+      case "o" => 8
+      case "b" => 2
+      case _ => Builder.error(s"Invalid base $base"); 2
+    }
+    BigInt(num.filterNot(_ == '_'), radix)
+  }
+
+  private def parsedWidth(n: String) =
+    if (n(0) == 'b') {
+      Width(n.length-1)
+    } else if (n(0) == 'h') {
+      Width((n.length-1) * 4)
+    } else {
+      Width()
+    }
+}
+
+object UInt extends UIntFactory
+
+sealed class SInt private (dir: Direction, width: Width, lit: Option[SLit] = None)
+    extends Bits(dir, width, lit) with Num[SInt] {
+  private[Chisel] override def cloneTypeWidth(w: Width): this.type =
+    new SInt(dir, w).asInstanceOf[this.type]
+  private[Chisel] def toType = s"SInt$width"
+
+  override def := (that: Data): Unit = that match {
+    case _: SInt => this connect that
+    case _ => this badConnect that
+  }
+
+  override private[Chisel] def fromInt(value: BigInt): this.type = SInt(value).asInstanceOf[this.type]
+
+  def unary_- : SInt = SInt(0) - this
+  def unary_-% : SInt = SInt(0) -% this
+  /** add (width +1) operator */
+  def +& (other: SInt): SInt = binop(SInt((this.width max other.width) + 1), AddOp, other)
+  /** add (default - no growth) operator */
+  def + (other: SInt): SInt = this +% other
+  /** add (no growth) operator */
+  def +% (other: SInt): SInt = (this +& other).tail(1).asSInt
+  /** subtract (width +1) operator */
+  def -& (other: SInt): SInt = binop(SInt((this.width max other.width) + 1), SubOp, other)
+  /** subtract (default - no growth) operator */
+  def - (other: SInt): SInt = this -% other
+  /** subtract (no growth) operator */
+  def -% (other: SInt): SInt = (this -& other).tail(1).asSInt
+  def * (other: SInt): SInt = binop(SInt(this.width + other.width), TimesOp, other)
+  def * (other: UInt): SInt = binop(SInt(this.width + other.width), TimesOp, other)
+  def / (other: SInt): SInt = binop(SInt(this.width), DivideOp, other)
+  def % (other: SInt): SInt = binop(SInt(this.width), RemOp, other)
+
+  def & (other: SInt): SInt = binop(UInt(this.width max other.width), BitAndOp, other).asSInt
+  def | (other: SInt): SInt = binop(UInt(this.width max other.width), BitOrOp, other).asSInt
+  def ^ (other: SInt): SInt = binop(UInt(this.width max other.width), BitXorOp, other).asSInt
+
+  /** Returns this wire bitwise-inverted. */
+  def unary_~ : SInt = unop(UInt(width = width), BitNotOp).asSInt
+
+  def < (other: SInt): Bool = compop(LessOp, other)
+  def > (other: SInt): Bool = compop(GreaterOp, other)
+  def <= (other: SInt): Bool = compop(LessEqOp, other)
+  def >= (other: SInt): Bool = compop(GreaterEqOp, other)
+  def != (other: SInt): Bool = compop(NotEqualOp, other)
+  def =/= (other: SInt): Bool = compop(NotEqualOp, other)
+  def === (other: SInt): Bool = compop(EqualOp, other)
+  def abs(): UInt = Mux(this < SInt(0), (-this).asUInt, this.asUInt)
+
+  def << (other: Int): SInt = binop(SInt(this.width + other), ShiftLeftOp, other)
+  def << (other: BigInt): SInt = this << other.toInt
+  def << (other: UInt): SInt = binop(SInt(this.width.dynamicShiftLeft(other.width)), DynamicShiftLeftOp, other)
+  def >> (other: Int): SInt = binop(SInt(this.width.shiftRight(other)), ShiftRightOp, other)
+  def >> (other: BigInt): SInt = this >> other.toInt
+  def >> (other: UInt): SInt = binop(SInt(this.width), DynamicShiftRightOp, other)
+
+  def asUInt(): UInt = pushOp(DefPrim(UInt(this.width), AsUIntOp, ref))
+  def asSInt(): SInt = this
+}
+
+object SInt {
+  /** Create an SInt type with inferred width. */
+  def apply(): SInt = apply(NO_DIR, Width())
+  /** Create an SInt type or port with fixed width. */
+  def apply(dir: Direction = NO_DIR, width: Int): SInt = apply(dir, Width(width))
+  /** Create an SInt port with inferred width. */
+  def apply(dir: Direction): SInt = apply(dir, Width())
+
+  /** Create an SInt literal with inferred width. */
+  def apply(value: BigInt): SInt = apply(value, Width())
+  /** Create an SInt literal with fixed width. */
+  def apply(value: BigInt, width: Int): SInt = apply(value, Width(width))
+
+  /** Create an SInt type with specified width. */
+  def apply(width: Width): SInt = new SInt(NO_DIR, width)
+  /** Create an SInt port with specified width. */
+  def apply(dir: Direction, width: Width): SInt = new SInt(dir, width)
+  /** Create an SInt literal with specified width. */
+  def apply(value: BigInt, width: Width): SInt = {
+    val lit = SLit(value, width)
+    new SInt(NO_DIR, lit.width, Some(lit))
+  }
+}
+
+// REVIEW TODO: Why does this extend UInt and not Bits? Does defining airth
+// operations on a Bool make sense?
+/** A data type for booleans, defined as a single bit indicating true or false.
+  */
+sealed class Bool(dir: Direction, lit: Option[ULit] = None) extends UInt(dir, Width(1), lit) {
+  private[Chisel] override def cloneTypeWidth(w: Width): this.type = {
+    require(!w.known || w.get == 1)
+    new Bool(dir).asInstanceOf[this.type]
+  }
+
+  override private[Chisel] def fromInt(value: BigInt): this.type = {
+    require(value == 0 || value == 1)
+    Bool(value == 1).asInstanceOf[this.type]
+  }
+
+  // REVIEW TODO: Why does this need to exist and have different conventions
+  // than Bits?
+  def & (other: Bool): Bool = binop(Bool(), BitAndOp, other)
+  def | (other: Bool): Bool = binop(Bool(), BitOrOp, other)
+  def ^ (other: Bool): Bool = binop(Bool(), BitXorOp, other)
+
+  /** Returns this wire bitwise-inverted. */
+  override def unary_~ : Bool = unop(Bool(), BitNotOp)
+
+  /** Outputs the logical OR of two Bools.
+   */
+  def || (that: Bool): Bool = this | that
+
+  /** Outputs the logical AND of two Bools.
+   */
+  def && (that: Bool): Bool = this & that
+}
+
+object Bool {
+  /** Creates an empty Bool.
+   */
+  def apply(dir: Direction = NO_DIR): Bool = new Bool(dir)
+
+  /** Creates Bool literal.
+   */
+  def apply(x: Boolean): Bool = new Bool(NO_DIR, Some(ULit(if (x) 1 else 0, Width(1))))
+}
+
+object Mux {
+  /** Creates a mux, whose output is one of the inputs depending on the
+    * value of the condition.
+    *
+    * @param cond condition determining the input to choose
+    * @param con the value chosen when `cond` is true
+    * @param alt the value chosen when `cond` is false
+    * @example
+    * {{{
+    * val muxOut = Mux(data_in === UInt(3), UInt(3, 4), UInt(0, 4))
+    * }}}
+    */
+  def apply[T <: Data](cond: Bool, con: T, alt: T): T = (con, alt) match {
+    // Handle Mux(cond, UInt, Bool) carefully so that the concrete type is UInt
+    case (c: Bool, a: Bool) => doMux(cond, c, a).asInstanceOf[T]
+    case (c: UInt, a: Bool) => doMux(cond, c, a << 0).asInstanceOf[T]
+    case (c: Bool, a: UInt) => doMux(cond, c << 0, a).asInstanceOf[T]
+    case (c: Bits, a: Bits) => doMux(cond, c, a).asInstanceOf[T]
+    case _ => doAggregateMux(cond, con, alt)
+  }
+
+  private def doMux[T <: Data](cond: Bool, con: T, alt: T): T = {
+    require(con.getClass == alt.getClass, s"can't Mux between ${con.getClass} and ${alt.getClass}")
+    val d = alt.cloneTypeWidth(con.width max alt.width)
+    pushOp(DefPrim(d, MultiplexOp, cond.ref, con.ref, alt.ref))
+  }
+
+  private def doAggregateMux[T <: Data](cond: Bool, con: T, alt: T): T = {
+    require(con.getClass == alt.getClass, s"can't Mux between ${con.getClass} and ${alt.getClass}")
+    for ((c, a) <- con.flatten zip alt.flatten)
+      require(c.width == a.width, "can't Mux between aggregates of different width")
+    doMux(cond, con, alt)
+  }
+}
+
-- 
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