Avoid silently truncating BigInt to Int

- Introduce internal helper `castToInt`, which issues an error when the input
BigInt can't be represented as Int.

- Use `castToInt` wherever we were using `toInt` in a potentially unsafe way.

2 files changed, 17 insertions, 8 deletions

diff --git a/chiselFrontend/src/main/scala/chisel3/core/Bits.scala b/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
index 43a851ed..e35d12f0 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Bits.scala
@@ -162,7 +162,7 @@ sealed abstract class Bits(private[chisel3] val width: Width) extends Element wi
     // This preserves old behavior while a more more consistent API is under debate
     // See https://github.com/freechipsproject/chisel3/issues/867
     litOption.map { value =>
-      (((value >> x.toInt) & 1) == 1).asBool
+      (((value >> castToInt(x, "Index")) & 1) == 1).asBool
     }.getOrElse {
       requireIsHardware(this, "bits to be indexed")
       pushOp(DefPrim(sourceInfo, Bool(), BitsExtractOp, this.ref, ILit(x), ILit(x)))
@@ -238,7 +238,7 @@ sealed abstract class Bits(private[chisel3] val width: Width) extends Element wi
 
   /** @group SourceInfoTransformMacro */
   final def do_apply(x: BigInt, y: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
-    apply(x.toInt, y.toInt)
+    apply(castToInt(x, "High index"), castToInt(y, "Low index"))
 
   private[core] def unop[T <: Data](sourceInfo: SourceInfo, dest: T, op: PrimOp): T = {
     requireIsHardware(this, "bits operated on")
@@ -866,13 +866,13 @@ sealed class UInt private[core] (width: Width) extends Bits(width) with Num[UInt
   override def do_<< (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
     binop(sourceInfo, UInt(this.width + that), ShiftLeftOp, validateShiftAmount(that))
   override def do_<< (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
-    this << that.toInt
+    this << castToInt(that, "Shift amount")
   override def do_<< (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
     binop(sourceInfo, UInt(this.width.dynamicShiftLeft(that.width)), DynamicShiftLeftOp, that)
   override def do_>> (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
     binop(sourceInfo, UInt(this.width.shiftRight(that)), ShiftRightOp, validateShiftAmount(that))
   override def do_>> (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
-    this >> that.toInt
+    this >> castToInt(that, "Shift amount")
   override def do_>> (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): UInt =
     binop(sourceInfo, UInt(this.width), DynamicShiftRightOp, that)
 
@@ -1155,13 +1155,13 @@ sealed class SInt private[core] (width: Width) extends Bits(width) with Num[SInt
   override def do_<< (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
     binop(sourceInfo, SInt(this.width + that), ShiftLeftOp, validateShiftAmount(that))
   override def do_<< (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
-    this << that.toInt
+    this << castToInt(that, "Shift amount")
   override def do_<< (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
     binop(sourceInfo, SInt(this.width.dynamicShiftLeft(that.width)), DynamicShiftLeftOp, that)
   override def do_>> (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
     binop(sourceInfo, SInt(this.width.shiftRight(that)), ShiftRightOp, validateShiftAmount(that))
   override def do_>> (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
-    this >> that.toInt
+    this >> castToInt(that, "Shift amount")
   override def do_>> (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): SInt =
     binop(sourceInfo, SInt(this.width), DynamicShiftRightOp, that)
 
@@ -1602,13 +1602,13 @@ sealed class FixedPoint private (width: Width, val binaryPoint: BinaryPoint)
   override def do_<< (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
     binop(sourceInfo, FixedPoint(this.width + that, this.binaryPoint), ShiftLeftOp, validateShiftAmount(that))
   override def do_<< (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
-    (this << that.toInt).asFixedPoint(this.binaryPoint)
+    (this << castToInt(that, "Shift amount")).asFixedPoint(this.binaryPoint)
   override def do_<< (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
     binop(sourceInfo, FixedPoint(this.width.dynamicShiftLeft(that.width), this.binaryPoint), DynamicShiftLeftOp, that)
   override def do_>> (that: Int)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
     binop(sourceInfo, FixedPoint(this.width.shiftRight(that), this.binaryPoint), ShiftRightOp, validateShiftAmount(that))
   override def do_>> (that: BigInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
-    (this >> that.toInt).asFixedPoint(this.binaryPoint)
+    (this >> castToInt(that, "Shift amount")).asFixedPoint(this.binaryPoint)
   override def do_>> (that: UInt)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions): FixedPoint =
     binop(sourceInfo, FixedPoint(this.width, this.binaryPoint), DynamicShiftRightOp, that)
 
diff --git a/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala b/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
index 4105a699..1163171c 100644
--- a/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
+++ b/chiselFrontend/src/main/scala/chisel3/internal/Builder.scala
@@ -378,3 +378,12 @@ object DynamicNamingStack {
     prefixRef
   }
 }
+
+/** Casts BigInt to Int, issuing an error when the input isn't representable. */
+private[chisel3] object castToInt {
+  def apply(x: BigInt, msg: String): Int = {
+    val res = x.toInt
+    require(x == res, s"$msg $x is too large to be represented as Int")
+    res
+  }
+}