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// SPDX-License-Identifier: Apache-2.0
package chiselTests.util
import chisel3._
import chisel3.util._
import chiseltest._
import chiseltest.formal._
import org.scalatest.flatspec.AnyFlatSpec
class GrayCodeTests extends AnyFlatSpec with ChiselScalatestTester with Formal {
behavior.of("GrayCode")
val Widths = Seq(1, 2, 3, 5, 8, 17, 65)
Widths.foreach { w =>
it should s"maintain identity (width=$w)" in {
verify(new GrayCodeIdentityCheck(w), Seq(BoundedCheck(1)))
}
it should s"ensure hamming distance of one (width=$w)" in {
verify(new GrayCodeHammingCheck(w), Seq(BoundedCheck(1)))
}
}
}
/** Checks that when we go from binary -> gray -> binary the result is always the same as the input. */
private class GrayCodeIdentityCheck(width: Int) extends Module {
val in = IO(Input(UInt(width.W)))
val gray = BinaryToGray(in)
val out = GrayToBinary(gray)
assert(in === out, "%b -> %b -> %b", in, gray, out)
}
/** Checks that if we increment the binary number, the gray code equivalent only changes by one bit. */
private class GrayCodeHammingCheck(width: Int) extends Module {
val a = IO(Input(UInt(width.W)))
val b = a + 1.U
val aGray = BinaryToGray(a)
val bGray = BinaryToGray(b)
val hamming = PopCount(aGray ^ bGray)
assert(hamming === 1.U, "%b ^ %b = %b", aGray, bGray, hamming)
}
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