Add a benchmark for RSP accumulator

package.json

@@ -25,6 +25,7 @@
   "dependencies": {
     "@popperjs/core": "^2.11.8",
     "bootstrap": "^5.3.2",
-    "lil-gui": "^0.18.2"
+    "lil-gui": "^0.18.2",
+    "mitata": "^0.1.6"
   }
 }

src/rsp.bench.js

@@ -0,0 +1,65 @@
+import { run, bench, group } from 'mitata';
+
+const vAccMem = new ArrayBuffer(8 * 8); // Actually 48 bits, not 64. 
+const vAcc = new BigInt64Array(vAccMem);
+const vAccS32 = new Int32Array(vAccMem);
+const vAccU32 = new Uint32Array(vAccMem);
+const vAccS16 = new Int16Array(vAccMem);
+const vAccU16 = new Uint16Array(vAccMem);
+
+group('updateAccU32', () => {
+  bench('updateAccU32Orig', () => {
+    updateAccU32Orig(0, 0x0001_0000);
+  });
+  bench('updateAccU32New', () => {
+    updateAccU32New(0, 0x0001_0000);
+  });
+});
+
+group('updateAcc32SignedShift16', () => {
+  bench('updateAcc32SignedShift16Orig', () => {
+    updateAcc32SignedShift16Orig(0, 0x0001_0000);
+  });
+  bench('updateAcc32SignedShift16New', () => {
+    updateAcc32SignedShift16New(0, 0x0001_0000);
+  });
+});
+
+function setAccS48(el, v) { vAcc[el] = BigInt.asIntN(48, v); }
+
+function updateAccU32Orig(el, v) {
+  setAccS48(el, vAcc[el] + BigInt(v));
+}
+
+function updateAccU32New(el, v) {
+  const x0 = vAccU32[(el * 2) + 0];
+  const x1 = vAccS32[(el * 2) + 1];
+  const y0 = v;
+
+  const z0 = x0 + y0;
+  const c = ((x0 & y0) | ((x0 | y0) & ~z0)) >>> 31;
+  const z1 = x1 + c;
+
+  vAccS32[(el * 2) + 1] = (z1 << 16) >> 16;  // truncate to s48 / sign extend
+  vAccU32[(el * 2) + 0] = z0;
+}
+
+function updateAcc32SignedShift16Orig(el, v) {
+  setAccS48(el, vAcc[el] + (BigInt(v) << 16n));
+}
+
+function updateAcc32SignedShift16New(el, v) {
+  const x0 = vAccU32[(el * 2) + 0];
+  const x1 = vAccS32[(el * 2) + 1];
+  const y0 = v << 16;
+  const y1 = v >> 16;
+
+  const z0 = x0 + y0;
+  const c = ((x0 & y0) | ((x0 | y0) & ~z0)) >>> 31;
+  const z1 = x1 + y1 + c;
+
+  vAccS32[(el * 2) + 1] = (z1 << 16) >> 16;  // truncate to s48 / sign extend
+  vAccU32[(el * 2) + 0] = z0;
+}
+
+await run({});