diff options
| -rw-r--r-- | src/main/scala/chisel3/util/Math.scala | 36 | ||||
| -rw-r--r-- | src/test/scala/chiselTests/Math.scala | 50 |
2 files changed, 84 insertions, 2 deletions
diff --git a/src/main/scala/chisel3/util/Math.scala b/src/main/scala/chisel3/util/Math.scala index f9278c7d..105b4161 100644 --- a/src/main/scala/chisel3/util/Math.scala +++ b/src/main/scala/chisel3/util/Math.scala @@ -5,8 +5,7 @@ package chisel3.util -import chisel3._ -import chisel3.internal.chiselRuntimeDeprecated +import chisel3.internal /** Compute the log2 of a Scala integer, rounded up, with min value of 1. * Useful for getting the number of bits needed to represent some number of states (in - 1), @@ -99,3 +98,36 @@ object isPow2 { def apply(in: BigInt): Boolean = in > 0 && ((in & (in-1)) == 0) def apply(in: Int): Boolean = apply(BigInt(in)) } + + +object unsignedBitLength { + /** Return the number of bits required to encode a specific value, assuming no sign bit is required. + * + * Basically, `n.bitLength`. NOTE: This will return 0 for a value of 0. + * This reflects the Chisel assumption that a zero width wire has a value of 0. + * @param in - the number to be encoded. + * @return - an Int representing the number of bits to encode. + */ + def apply(in: BigInt): Int = { + require(in >= 0) + in.bitLength + } +} + +object signedBitLength { + /** Return the number of bits required to encode a specific value, assuming a sign bit is required. + * + * Basically, 0 for 0, 1 for -1, and `n.bitLength` + 1 for everything else. + * This reflects the Chisel assumption that a zero width wire has a value of 0. + * @param in - the number to be encoded. + * @return - an Int representing the number of bits to encode. + */ + def apply(in: BigInt): Int = { + in.toInt match { + case 0 => 0 + case -1 => 1 + case _ => in.bitLength + 1 + } + + } +} diff --git a/src/test/scala/chiselTests/Math.scala b/src/test/scala/chiselTests/Math.scala new file mode 100644 index 00000000..aa32a828 --- /dev/null +++ b/src/test/scala/chiselTests/Math.scala @@ -0,0 +1,50 @@ +// See LICENSE for license details. + +package chiselTests + +import org.scalacheck.Shrink + +class Math extends ChiselPropSpec { + import chisel3.util._ + // Disable shrinking on error. + implicit val noShrinkListVal = Shrink[List[Int]](_ => Stream.empty) + implicit val noShrinkInt = Shrink[Int](_ => Stream.empty) + + property ("unsignedBitLength is computed correctly") { + forAll(safeUIntWidth) { case (width: Int) => + for ( offset <- List(-1, 0, 1)) { + val n = (1 << width) + offset + if (n >= 0) { + val d = unsignedBitLength(n) + val t = if (n == 0) 0 else if (offset < 0) width else width + 1 + d shouldEqual (t) + } + } + } + } + + property ("signedBitLength is computed correctly") { + forAll(safeUIntWidth) { case (width: Int) => + for ( offset <- List(-1, 0, 1)) { + for ( mult <- List(-1, +1)) { + val n = ((1 << (width - 1)) + offset) * mult + val d = signedBitLength(n) + val t = n match { + case -2 => 2 + case -1 => 1 + case 0 => 0 + case 1 => 2 + case 2 => 3 + case _ => + if (n > 0) { + if (offset < 0) width else width + 1 + } else { + if (offset > 0) width + 1 else width + } + } + d shouldEqual (t) + } + } + } + } +} |