feat: add fp8 e4m3 decode support

src/main/scala/radiance/core/TensorDPU.scala

@@ -7,6 +7,37 @@ import chisel3._
 import chisel3.util._
 import freechips.rocketchip.tile
 
+object FP8E4M3 {
+  private val Bias = 7
+
+  private def decodeToFloat(bits: Int): Float = {
+    val sign = (bits >> 7) & 0x1
+    val exp = (bits >> 3) & 0xf
+    val frac = bits & 0x7
+
+    val magnitude =
+      if (exp == 0) {
+        if (frac == 0) 0.0
+        else (frac.toDouble / 8.0) * Math.pow(2.0, 1 - Bias)
+      } else {
+        (1.0 + frac.toDouble / 8.0) * Math.pow(2.0, exp - Bias)
+      }
+
+    val value = if (sign == 1) -magnitude else magnitude
+    value.toFloat
+  }
+
+  private def fp32Bits(bits: Int): BigInt = {
+    BigInt(java.lang.Float.floatToRawIntBits(decodeToFloat(bits)).toLong & 0xffffffffL)
+  }
+
+  def toFloat32(x: UInt): UInt = {
+    MuxLookup(x, 0.U(32.W))((0 until 256).map { bits =>
+      bits.U(8.W) -> fp32Bits(bits).U(32.W)
+    })
+  }
+}
+
 // Implements the four-element dot product (FEDP) unit in Volta Tensor Cores.
 // `half`: if True, generate fp16 MACs; if False fp32.
 class TensorDotProductUnit(

src/test/scala/radiance/FP8E4M3Test.scala

@@ -0,0 +1,35 @@
+package radiance.core
+
+import chisel3._
+import chiseltest._
+import org.scalatest.flatspec.AnyFlatSpec
+
+class FP8E4M3DecodeHarness extends Module {
+  val io = IO(new Bundle {
+    val in = Input(UInt(8.W))
+    val out = Output(UInt(32.W))
+  })
+
+  io.out := FP8E4M3.toFloat32(io.in)
+}
+
+class FP8E4M3Test extends AnyFlatSpec with ChiselScalatestTester {
+  behavior of "FP8E4M3"
+
+  it should "decode representative E4M3 values to FP32 bits" in {
+    test(new FP8E4M3DecodeHarness) { c =>
+      Seq(
+        0x00 -> 0x00000000L,
+        0x80 -> 0x80000000L,
+        0x38 -> 0x3f800000L,
+        0x40 -> 0x40000000L,
+        0x30 -> 0x3f000000L,
+        0x3c -> 0x3fc00000L
+      ).foreach { case (fp8, fp32) =>
+        c.io.in.poke(fp8.U)
+        c.clock.step()
+        c.io.out.expect(fp32.U)
+      }
+    }
+  }
+}