Cleanup SIMD vector length setting

Simplify the logic.

Change-Id: I9e295bfb494b5abff2ff383c2fdab7d221e7b7bd

hdl/chisel/src/kelvin/Parameters.scala

diff --git a/hdl/chisel/src/kelvin/Parameters.scala b/hdl/chisel/src/kelvin/Parameters.scala
index 2024883..4d1ab66 100644
--- a/hdl/chisel/src/kelvin/Parameters.scala
+++ b/hdl/chisel/src/kelvin/Parameters.scala
@@ -10,7 +10,12 @@
     val big = 2
   }
 
-  val core = sys.env.get("KELVIN_SIMD").getOrElse("256").toInt match {
+  // Vector Length (register-file and compute).
+  // 128 = faster builds, but not production(?).
+  val vectorBits = sys.env.get("KELVIN_SIMD").getOrElse("256").toInt
+  assert(vectorBits == 512 || vectorBits == 256 || vectorBits == 128)
+
+  val core = vectorBits match {
     case 128 => Core.tiny
     case 256 => Core.little
     case 512 => Core.big
@@ -21,16 +26,7 @@
   val instructionBits = 32
   val instructionLanes = 4
 
-  // Vector Length (register-file and compute).
-  val vectorBits = core match {
-    case Core.tiny   => 128
-    case Core.little => 256
-    case Core.big    => 512
-  }
-
   val vectorCountBits = log2Ceil(vectorBits / 8) + 1 + 2  // +2 stripmine
-  assert(vectorBits == 512 || vectorBits == 256
-      || vectorBits == 128)  // 128 = faster builds, but not production(?).
 
   // Vector queue.
   val vectorFifoDepth = 16

tests/verilator_sim/kelvin/kelvin_cfg.h

diff --git a/tests/verilator_sim/kelvin/kelvin_cfg.h b/tests/verilator_sim/kelvin/kelvin_cfg.h
index ef2a2b5..424a507 100644
--- a/tests/verilator_sim/kelvin/kelvin_cfg.h
+++ b/tests/verilator_sim/kelvin/kelvin_cfg.h
@@ -1,14 +1,12 @@
+// Copyright 2023 Google LLC.
+
 #ifndef TESTS_VERILATOR_SIM_KELVIN_KELVIN_CFG_H_
 #define TESTS_VERILATOR_SIM_KELVIN_KELVIN_CFG_H_
 
 #ifndef KELVIN_SIMD
 #error KELVIN_SIMD must be defined in Environment or Makefile.
-#elif KELVIN_SIMD == 128
-constexpr int kVector = 128;
-#elif KELVIN_SIMD == 256
-constexpr int kVector = 256;
-#elif KELVIN_SIMD == 512
-constexpr int kVector = 512;
+#elif (KELVIN_SIMD == 128) || (KELVIN_SIMD == 256) || (KELVIN_SIMD == 512)
+constexpr int kVector = KELVIN_SIMD;
 #else
 #error KELVIN_SIMD unsupported configuration.
 #endif