Merge pull request #39 from ucb-bar/coresplit

Break Core.scala into bite-sized pieces

1 files changed, 72 insertions, 0 deletions

diff --git a/src/main/scala/Chisel/BitPat.scala b/src/main/scala/Chisel/BitPat.scala
new file mode 100644
index 00000000..1f0182e4
--- /dev/null
+++ b/src/main/scala/Chisel/BitPat.scala
@@ -0,0 +1,72 @@
+// See LICENSE for license details.
+
+package Chisel
+
+object BitPat {
+  /** Parses a bit pattern string into (bits, mask, width).
+    *
+    * @return bits the literal value, with don't cares being 0
+    * @return mask the mask bits, with don't cares being 0 and cares being 1
+    * @return width the number of bits in the literal, including values and
+    * don't cares.
+    */
+  private def parse(x: String): (BigInt, BigInt, Int) = {
+    // REVIEW TODO: can this be merged with literal parsing creating one unified
+    // Chisel string to value decoder (which can also be invoked by libraries
+    // and testbenches?
+    // REVIEW TODO: Verilog Xs also handle octal and hex cases.
+    require(x.head == 'b', "BitPats must be in binary and be prefixed with 'b'")
+    var bits = BigInt(0)
+    var mask = BigInt(0)
+    for (d <- x.tail) {
+      if (d != '_') {
+        if (!"01?".contains(d)) Builder.error({"Literal: " + x + " contains illegal character: " + d})
+        mask = (mask << 1) + (if (d == '?') 0 else 1)
+        bits = (bits << 1) + (if (d == '1') 1 else 0)
+      }
+    }
+    (bits, mask, x.length - 1)
+  }
+
+  /** Creates a [[BitPat]] literal from a string.
+   *
+    * @param n the literal value as a string, in binary, prefixed with 'b'
+    * @note legal characters are '0', '1', and '?', as well as '_' as white
+    * space (which are ignored)
+    */
+  def apply(n: String): BitPat = {
+    val (bits, mask, width) = parse(n)
+    new BitPat(bits, mask, width)
+  }
+
+  /** Creates a [[BitPat]] of all don't cares of a specified width. */
+  // REVIEW TODO: is this really necessary? if so, can there be a better name?
+  def DC(width: Int): BitPat = BitPat("b" + ("?" * width))
+
+  // BitPat <-> UInt
+  /** enable conversion of a bit pattern to a UInt */
+  // REVIEW TODO: Doesn't having a BitPat with all mask bits high defeat the
+  // point of using a BitPat in the first place?
+  implicit def BitPatToUInt(x: BitPat): UInt = {
+    require(x.mask == (BigInt(1) << x.getWidth) - 1)
+    UInt(x.value, x.getWidth)
+  }
+
+  /** create a bit pattern from a UInt */
+  // REVIEW TODO: Similar, what is the point of this?
+  implicit def apply(x: UInt): BitPat = {
+    require(x.isLit)
+    BitPat("b" + x.litValue.toString(2))
+  }
+}
+
+// TODO: Break out of Core? (this doesn't involve FIRRTL generation)
+/** Bit patterns are literals with masks, used to represent values with don't
+  * cares. Equality comparisons will ignore don't care bits (for example,
+  * BitPat(0b10?1) === UInt(0b1001) and UInt(0b1011)).
+  */
+sealed class BitPat(val value: BigInt, val mask: BigInt, width: Int) {
+  def getWidth: Int = width
+  def === (other: UInt): Bool = UInt(value) === (other & UInt(mask))
+  def != (other: UInt): Bool = !(this === other)
+}