Merge pull request #37 from ucb-bar/utilsplit

Break out Utils.scala into smaller portions

1 files changed, 62 insertions, 0 deletions

diff --git a/src/main/scala/Chisel/util/OneHot.scala b/src/main/scala/Chisel/util/OneHot.scala
new file mode 100644
index 00000000..38b96511
--- /dev/null
+++ b/src/main/scala/Chisel/util/OneHot.scala
@@ -0,0 +1,62 @@
+// See LICENSE for license details.
+
+/** Circuit generators for working with one-hot representations.
+  */
+
+package Chisel
+
+/** Converts from One Hot Encoding to a UInt indicating which bit is active
+  * This is the inverse of [[Chisel.UIntToOH UIntToOH]]*/
+object OHToUInt {
+  def apply(in: Seq[Bool]): UInt = apply(Vec(in))
+  def apply(in: Vec[Bool]): UInt = apply(in.toBits, in.size)
+  def apply(in: Bits): UInt = apply(in, in.getWidth)
+
+  def apply(in: Bits, width: Int): UInt = {
+    if (width <= 2) {
+      Log2(in, width)
+    } else {
+      val mid = 1 << (log2Up(width)-1)
+      val hi = in(width-1, mid)
+      val lo = in(mid-1, 0)
+      Cat(hi.orR, apply(hi | lo, mid))
+    }
+  }
+}
+
+/** @return the bit position of the trailing 1 in the input vector
+  * with the assumption that multiple bits of the input bit vector can be set
+  * @example {{{ data_out := PriorityEncoder(data_in) }}}
+  */
+object PriorityEncoder {
+  def apply(in: Seq[Bool]): UInt = PriorityMux(in, (0 until in.size).map(UInt(_)))
+  def apply(in: Bits): UInt = apply(in.toBools)
+}
+
+/** Returns the one hot encoding of the input UInt.
+  */
+object UIntToOH
+{
+  def apply(in: UInt, width: Int = -1): UInt =
+    if (width == -1) {
+      UInt(1) << in
+    } else {
+      (UInt(1) << in(log2Up(width)-1,0))(width-1,0)
+    }
+}
+
+/** Returns a bit vector in which only the least-significant 1 bit in
+  the input vector, if any, is set.
+  */
+object PriorityEncoderOH
+{
+  private def encode(in: Seq[Bool]): UInt = {
+    val outs = Vec.tabulate(in.size)(i => UInt(BigInt(1) << i, in.size))
+    PriorityMux(in :+ Bool(true), outs :+ UInt(0, in.size))
+  }
+  def apply(in: Seq[Bool]): Vec[Bool] = {
+    val enc = encode(in)
+    Vec.tabulate(in.size)(enc(_))
+  }
+  def apply(in: Bits): UInt = encode((0 until in.getWidth).map(i => in(i)))
+}