refactor: extract typed spectrum math

src/trx-client/trx-frontend/trx-frontend-http/assets/web/generated/app.js

@@ -461,6 +461,69 @@
     return Math.max(stepBw, Math.round(clamped / stepBw) * stepBw);
   }
 
+  // src/features/spectrum/math.ts
+  function isNumericBins(value) {
+    return Array.isArray(value) ? value.every((item) => typeof item === "number") : ArrayBuffer.isView(value) && !(value instanceof DataView);
+  }
+  var base64Lookup = new Uint8Array(128).fill(255);
+  var base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+  for (let index = 0; index < base64Alphabet.length; index += 1) {
+    base64Lookup[base64Alphabet.charCodeAt(index)] = index;
+  }
+  var spectrumBinBuffer = new Int8Array(0);
+  function decodeBase64Int8(value) {
+    let end = value.length;
+    while (end > 0 && value.charCodeAt(end - 1) === 61) end -= 1;
+    const outputLength = end * 3 >>> 2;
+    if (spectrumBinBuffer.length !== outputLength) spectrumBinBuffer = new Int8Array(outputLength);
+    let outputIndex = 0;
+    for (let index = 0; index < end; ) {
+      const sextets = [0, 0, 0, 0];
+      for (let offset = 0; offset < 4 && index < end; offset += 1, index += 1) {
+        const code = value.charCodeAt(index);
+        const decoded = code < base64Lookup.length ? base64Lookup[code] : void 0;
+        if (decoded === void 0 || decoded === 255) throw new TypeError("Invalid base64 spectrum frame");
+        sextets[offset] = decoded;
+      }
+      const packed = (sextets[0] ?? 0) << 18 | (sextets[1] ?? 0) << 12 | (sextets[2] ?? 0) << 6 | (sextets[3] ?? 0);
+      if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed >> 16 & 255;
+      if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed >> 8 & 255;
+      if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed & 255;
+    }
+    return spectrumBinBuffer;
+  }
+  var nthScratch = new Float64Array(0);
+  function nthElement(values, target) {
+    if (values.length === 0 || target < 0 || target >= values.length) return null;
+    if (nthScratch.length < values.length) nthScratch = new Float64Array(values.length);
+    for (let index = 0; index < values.length; index += 1) nthScratch[index] = values[index] ?? 0;
+    let low = 0;
+    let high = values.length - 1;
+    while (low < high) {
+      const pivot = nthScratch[low + (high - low >> 1)] ?? 0;
+      let left = low;
+      let right = high;
+      while (left <= right) {
+        while ((nthScratch[left] ?? Infinity) < pivot) left += 1;
+        while ((nthScratch[right] ?? -Infinity) > pivot) right -= 1;
+        if (left <= right) {
+          const temporary = nthScratch[left] ?? 0;
+          nthScratch[left] = nthScratch[right] ?? 0;
+          nthScratch[right] = temporary;
+          left += 1;
+          right -= 1;
+        }
+      }
+      if (right < target) low = left;
+      if (target < left) high = right;
+    }
+    return nthScratch[target] ?? null;
+  }
+  function estimateNoiseFloorDb(bins) {
+    if (!isNumericBins(bins) || bins.length === 0) return null;
+    return nthElement(bins, Math.floor(bins.length * 0.15));
+  }
+
   // src/app.js
   void loadDecoderRegistry(refreshOperatorLayoutCapabilities);
   var authRole = null;
@@ -1814,7 +1877,7 @@
     return { startIdx, endIdx };
   }
   function pushOverviewWaterfallFrame(data) {
-    if (!overviewCanvas || !data || !isBinsArray(data.bins) || data.bins.length === 0) return;
+    if (!overviewCanvas || !data || !isNumericBins(data.bins) || data.bins.length === 0) return;
     overviewWaterfallRows.push(data.bins.slice());
     overviewWaterfallPushCount++;
     trimOverviewWaterfallRows();
@@ -1869,7 +1932,7 @@
     overviewWfTexHeight = iH;
     ensureWaterfallLut(pal, minDb, maxDb);
     function renderRow(dstY, srcBins) {
-      if (!isBinsArray(srcBins) || srcBins.length === 0) return;
+      if (!isNumericBins(srcBins) || srcBins.length === 0) return;
       const { startIdx, endIdx } = overviewVisibleBinWindow(lastSpectrumData, srcBins.length);
       const spanBins = Math.max(1, endIdx - startIdx);
       const rowBase = dstY * rowStride;
@@ -2440,7 +2503,7 @@
     });
   }
   function spectrumBinIndexForHz(data, hz) {
-    if (!data || !isBinsArray(data.bins) || data.bins.length < 2 || !Number.isFinite(hz)) {
+    if (!data || !isNumericBins(data.bins) || data.bins.length < 2 || !Number.isFinite(hz)) {
       return null;
     }
     const maxIdx = data.bins.length - 1;
@@ -2454,7 +2517,7 @@
     return 10 ** (clamped / 10);
   }
   function sweetSpotCandidateForFrame(data, freqHz, bandwidthHz) {
-    if (!data || !isBinsArray(data.bins) || data.bins.length < 16) {
+    if (!data || !isNumericBins(data.bins) || data.bins.length < 16) {
       return null;
     }
     if (!Number.isFinite(freqHz) || !Number.isFinite(bandwidthHz) || bandwidthHz <= 0) {
@@ -4590,7 +4653,7 @@ ${unsupportedBandSummary()}`;
     currentStyle,
     cssColorToRgba,
     rgbaWithAlpha,
-    isBinsArray,
+    isBinsArray: isNumericBins,
     estimateNoiseFloorDb,
     spectrumVisibleRange,
     drawSpectrum,
@@ -4938,7 +5001,7 @@ ${unsupportedBandSummary()}`;
       if (!sdrSquelchSupported) return;
       let pct = 0;
       const data = lastSpectrumData || window.lastSpectrumData;
-      if (data && isBinsArray(data.bins) && data.bins.length > 0) {
+      if (data && isNumericBins(data.bins) && data.bins.length > 0) {
         const noiseDb = estimateNoiseFloorDb(data.bins);
         if (noiseDb != null && Number.isFinite(noiseDb)) {
           const thresholdDb = noiseDb + 6;
@@ -6129,34 +6192,6 @@ ${unsupportedBandSummary()}`;
   var waterfallGamma = 1;
   var SPECTRUM_HEADROOM_DB = 20;
   var SPECTRUM_SMOOTH_ALPHA = 0.42;
-  var _b64Lut = new Uint8Array(128);
-  for (let i = 0; i < 128; i++) _b64Lut[i] = 255;
-  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".split("").forEach((c, i) => {
-    _b64Lut[c.charCodeAt(0)] = i;
-  });
-  var _spectrumBinI8 = new Int8Array(0);
-  function isBinsArray(v) {
-    return Array.isArray(v) || ArrayBuffer.isView(v);
-  }
-  function decodeBase64ToInt8(b64) {
-    let end = b64.length;
-    while (end > 0 && b64.charCodeAt(end - 1) === 61) end--;
-    const outLen = end * 3 >>> 2;
-    if (_spectrumBinI8.length !== outLen) _spectrumBinI8 = new Int8Array(outLen);
-    const out = _spectrumBinI8;
-    let j = 0;
-    for (let i = 0; i < end; ) {
-      const a = _b64Lut[b64.charCodeAt(i++)];
-      const b = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-      const c = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-      const d = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-      const n = a << 18 | b << 12 | c << 6 | d;
-      if (j < outLen) out[j++] = n >> 16 & 255;
-      if (j < outLen) out[j++] = n >> 8 & 255;
-      if (j < outLen) out[j++] = n & 255;
-    }
-    return out;
-  }
   var spectrumCrosshairX = null;
   var spectrumCrosshairY = null;
   var _bwDragEdge = null;
@@ -6231,13 +6266,13 @@ ${unsupportedBandSummary()}`;
     let removeCount = 0;
     for (let i = 0; i < spectrumPeakHoldFrames.length; i++) {
       const f = spectrumPeakHoldFrames[i];
-      if (f && isBinsArray(f.bins) && now - f.t <= holdMs) break;
+      if (f && isNumericBins(f.bins) && now - f.t <= holdMs) break;
       removeCount++;
     }
     if (removeCount > 0) spectrumPeakHoldFrames.splice(0, removeCount);
   }
   function pushSpectrumPeakHoldFrame(frame) {
-    if (!frame || !isBinsArray(frame.bins) || frame.bins.length === 0) {
+    if (!frame || !isNumericBins(frame.bins) || frame.bins.length === 0) {
       clearSpectrumPeakHoldFrames();
       return;
     }
@@ -6256,56 +6291,26 @@ ${unsupportedBandSummary()}`;
   }
   function buildSpectrumPeakHoldBins(currentBins) {
     const holdMs = Math.max(0, Number.isFinite(overviewPeakHoldMs) ? overviewPeakHoldMs : 0);
-    if (holdMs <= 0 || !isBinsArray(currentBins) || currentBins.length === 0) {
+    if (holdMs <= 0 || !isNumericBins(currentBins) || currentBins.length === 0) {
       return null;
     }
     pruneSpectrumPeakHoldFrames();
     if (spectrumPeakHoldFrames.length === 0) return null;
     const peakBins = currentBins.slice();
     for (const frame of spectrumPeakHoldFrames) {
-      if (!frame || !isBinsArray(frame.bins) || frame.bins.length !== peakBins.length) continue;
+      if (!frame || !isNumericBins(frame.bins) || frame.bins.length !== peakBins.length) continue;
       for (let i = 0; i < peakBins.length; i++) {
         if (frame.bins[i] > peakBins[i]) peakBins[i] = frame.bins[i];
       }
     }
     return peakBins;
   }
-  function estimateNoiseFloorDb(bins) {
-    if (!isBinsArray(bins) || bins.length === 0) return null;
-    const k = Math.floor(bins.length * 0.15);
-    return nthElement(bins, k);
-  }
-  function nthElement(arr, k) {
-    const tmp = _nthScratch.length >= arr.length ? _nthScratch : new Float64Array(arr.length);
-    if (tmp.length > _nthScratch.length) _nthScratch = tmp;
-    for (let i = 0; i < arr.length; i++) tmp[i] = arr[i];
-    let lo = 0, hi = arr.length - 1;
-    while (lo < hi) {
-      const pivot = tmp[lo + (hi - lo >> 1)];
-      let i = lo, j = hi;
-      while (i <= j) {
-        while (tmp[i] < pivot) i++;
-        while (tmp[j] > pivot) j--;
-        if (i <= j) {
-          const t = tmp[i];
-          tmp[i] = tmp[j];
-          tmp[j] = t;
-          i++;
-          j--;
-        }
-      }
-      if (j < k) lo = i;
-      if (k < i) hi = j;
-    }
-    return tmp[k];
-  }
-  var _nthScratch = new Float64Array(0);
   var _smoothBins = [];
   function buildSpectrumRenderData(frame) {
-    if (!frame || !isBinsArray(frame.bins)) return frame;
+    if (!frame || !isNumericBins(frame.bins)) return frame;
     const n = frame.bins.length;
     const prev = lastSpectrumRenderData;
-    const canBlend = prev && isBinsArray(prev.bins) && prev.bins.length === n && prev.sample_rate === frame.sample_rate && prev.center_hz === frame.center_hz;
+    const canBlend = prev && isNumericBins(prev.bins) && prev.bins.length === n && prev.sample_rate === frame.sample_rate && prev.center_hz === frame.center_hz;
     if (_smoothBins.length !== n) _smoothBins = new Array(n);
     const src = frame.bins;
     if (canBlend) {
@@ -6339,7 +6344,7 @@ ${unsupportedBandSummary()}`;
     return range.visLoHz + cssX / cssW * range.visSpanHz;
   }
   function nearestSpectrumPeak(cssX, cssW, data) {
-    if (!data || !isBinsArray(data.bins) || data.bins.length === 0 || cssW <= 0) {
+    if (!data || !isNumericBins(data.bins) || data.bins.length === 0 || cssW <= 0) {
       return null;
     }
     const bins = data.bins;
@@ -6400,7 +6405,7 @@ ${unsupportedBandSummary()}`;
     return nearestSpectrumPeakHz(cssX, cssW, data) ?? Math.round(canvasXToHz(cssX, cssW, range));
   }
   function visibleSpectrumPeakIndices(data, limit = 24) {
-    if (!data || !isBinsArray(data.bins) || data.bins.length < 3) {
+    if (!data || !isNumericBins(data.bins) || data.bins.length < 3) {
       return [];
     }
     const bins = data.bins;
@@ -6470,7 +6475,7 @@ ${unsupportedBandSummary()}`;
         const sampleRate = Number(evt.data.slice(commaA + 1, commaB));
         const b64 = evt.data.slice(commaB + 1);
         const hadSpectrum = !!lastSpectrumData;
-        const bins = decodeBase64ToInt8(b64);
+        const bins = decodeBase64Int8(b64);
         const rds = lastSpectrumData?.rds;
         lastSpectrumData = { bins, center_hz: centerHz, sample_rate: sampleRate, rds };
         window.lastSpectrumData = lastSpectrumData;
@@ -6914,7 +6919,7 @@ ${unsupportedBandSummary()}`;
       spectrumTmpFillPoints.push(binX(i), binYFromBins(bins, i));
     }
     spectrumGl.drawFilledArea(spectrumTmpFillPoints, H, cssColorToRgba(pal.spectrumFill));
-    if (isBinsArray(peakHoldBins) && peakHoldBins.length === n) {
+    if (isNumericBins(peakHoldBins) && peakHoldBins.length === n) {
       spectrumTmpPeakPoints.length = 0;
       for (let i = 0; i < n; i++) {
         spectrumTmpPeakPoints.push(binX(i), binYFromBins(peakHoldBins, i));
@@ -7011,7 +7016,7 @@ ${unsupportedBandSummary()}`;
   window.addEventListener("resize", _updateCachedCanvasSizes);
   _updateCachedCanvasSizes();
   function pushSpectrumWaterfallFrame(data) {
-    if (!spectrumWaterfallCanvas || !data || !isBinsArray(data.bins) || data.bins.length === 0) return;
+    if (!spectrumWaterfallCanvas || !data || !isNumericBins(data.bins) || data.bins.length === 0) return;
     spectrumWfRows.push(data.bins.slice());
     spectrumWfPushCount++;
     trimSpectrumWaterfallRows();
@@ -7067,7 +7072,7 @@ ${unsupportedBandSummary()}`;
     spectrumWfTexHeight = iH;
     ensureWaterfallLut(pal, minDb, maxDb);
     function renderRow(dstY, srcBins) {
-      if (!isBinsArray(srcBins) || srcBins.length === 0) return;
+      if (!isNumericBins(srcBins) || srcBins.length === 0) return;
       const { startIdx, endIdx } = overviewVisibleBinWindow(lastSpectrumData, srcBins.length);
       const spanBins = Math.max(1, endIdx - startIdx);
       const rowBase = dstY * rowStride;
@@ -7528,7 +7533,7 @@ ${unsupportedBandSummary()}`;
         } else {
           let auto = 30;
           const data = lastSpectrumData || window.lastSpectrumData;
-          if (data && isBinsArray(data.bins) && data.bins.length > 0) {
+          if (data && isNumericBins(data.bins) && data.bins.length > 0) {
             const noiseDb = estimateNoiseFloorDb(data.bins);
             if (noiseDb != null && Number.isFinite(noiseDb)) {
               const thresholdDb = noiseDb + 6;

src/trx-client/trx-frontend/trx-frontend-http/frontend/src/app.js

@@ -37,6 +37,11 @@ import {
   updateTabHistory,
 } from "./features/navigation/routes.js";
 import { estimateOccupiedBandwidth } from "./features/radio/auto-bandwidth.js";
+import {
+  decodeBase64Int8 as decodeBase64ToInt8,
+  estimateNoiseFloorDb,
+  isNumericBins as isBinsArray,
+} from "./features/spectrum/math.js";
 
 // --- Decoder registry (fetched from /decoders on load) ---
 void loadDecoderRegistry(refreshOperatorLayoutCapabilities);
@@ -6072,38 +6077,6 @@ let waterfallGamma = 1.0;
 const SPECTRUM_HEADROOM_DB = 20;
 const SPECTRUM_SMOOTH_ALPHA = 0.42;
 let _spectrumBinBuf = []; // Reusable buffer for SSE bin decoding
-// Fast base64 → Int8Array decoder using a lookup table.
-// Avoids atob() (which allocates a UTF-16 string) and the subsequent
-// charCodeAt loop, decoding directly into a reusable typed array.
-const _b64Lut = new Uint8Array(128);
-for (let i = 0; i < 128; i++) _b64Lut[i] = 255;
-"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".split("").forEach((c, i) => {
-  _b64Lut[c.charCodeAt(0)] = i;
-});
-let _spectrumBinI8 = new Int8Array(0); // Reusable typed-array bin buffer
-// Check if a value is an array-like bins buffer (Array or TypedArray).
-function isBinsArray(v) { return Array.isArray(v) || ArrayBuffer.isView(v); }
-function decodeBase64ToInt8(b64) {
-  // Strip trailing '=' padding
-  let end = b64.length;
-  while (end > 0 && b64.charCodeAt(end - 1) === 61) end--;
-  const outLen = (end * 3 >>> 2); // exact byte count without padding
-  if (_spectrumBinI8.length !== outLen) _spectrumBinI8 = new Int8Array(outLen);
-  const out = _spectrumBinI8;
-  let j = 0;
-  for (let i = 0; i < end; ) {
-    const a = _b64Lut[b64.charCodeAt(i++)];
-    const b = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-    const c = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-    const d = i < end ? _b64Lut[b64.charCodeAt(i++)] : 0;
-    const n = (a << 18) | (b << 12) | (c << 6) | d;
-    if (j < outLen) out[j++] = (n >> 16) & 0xff;
-    if (j < outLen) out[j++] = (n >> 8) & 0xff;
-    if (j < outLen) out[j++] = n & 0xff;
-  }
-  return out;
-}
-
 // Crosshair state (CSS coords relative to spectrum canvas).
 let spectrumCrosshairX = null;
 let spectrumCrosshairY = null;
@@ -6237,35 +6210,6 @@ function buildSpectrumPeakHoldBins(currentBins) {
   return peakBins;
 }
 
-// Estimate noise floor as the 15th-percentile of visible bins (same heuristic as Auto).
-// Uses O(N) nth-element selection instead of O(N log N) sort.
-function estimateNoiseFloorDb(bins) {
-  if (!isBinsArray(bins) || bins.length === 0) return null;
-  const k = Math.floor(bins.length * 0.15);
-  return nthElement(bins, k);
-}
-
-// O(N) average-case selection algorithm (Floyd-Rivest / quickselect).
-function nthElement(arr, k) {
-  const tmp = _nthScratch.length >= arr.length ? _nthScratch : new Float64Array(arr.length);
-  if (tmp.length > _nthScratch.length) _nthScratch = tmp;
-  for (let i = 0; i < arr.length; i++) tmp[i] = arr[i];
-  let lo = 0, hi = arr.length - 1;
-  while (lo < hi) {
-    const pivot = tmp[lo + ((hi - lo) >> 1)];
-    let i = lo, j = hi;
-    while (i <= j) {
-      while (tmp[i] < pivot) i++;
-      while (tmp[j] > pivot) j--;
-      if (i <= j) { const t = tmp[i]; tmp[i] = tmp[j]; tmp[j] = t; i++; j--; }
-    }
-    if (j < k) lo = i;
-    if (k < i) hi = j;
-  }
-  return tmp[k];
-}
-let _nthScratch = new Float64Array(0);
-
 // Pre-allocated buffer for smoothed spectrum bins (avoids .map() allocation per frame).
 let _smoothBins = [];
 

src/trx-client/trx-frontend/trx-frontend-http/frontend/src/features/spectrum/math.ts

@@ -0,0 +1,75 @@
+// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+export type NumericBins = number[] | Int8Array | Uint8Array | Float32Array | Float64Array;
+
+export function isNumericBins(value: unknown): value is NumericBins {
+  return Array.isArray(value)
+    ? value.every((item) => typeof item === "number")
+    : ArrayBuffer.isView(value) && !(value instanceof DataView);
+}
+
+const base64Lookup = new Uint8Array(128).fill(255);
+const base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+for (let index = 0; index < base64Alphabet.length; index += 1) {
+  base64Lookup[base64Alphabet.charCodeAt(index)] = index;
+}
+let spectrumBinBuffer = new Int8Array(0);
+
+export function decodeBase64Int8(value: string): Int8Array {
+  let end = value.length;
+  while (end > 0 && value.charCodeAt(end - 1) === 61) end -= 1;
+  const outputLength = end * 3 >>> 2;
+  if (spectrumBinBuffer.length !== outputLength) spectrumBinBuffer = new Int8Array(outputLength);
+  let outputIndex = 0;
+  for (let index = 0; index < end;) {
+    const sextets = [0, 0, 0, 0];
+    for (let offset = 0; offset < 4 && index < end; offset += 1, index += 1) {
+      const code = value.charCodeAt(index);
+      const decoded = code < base64Lookup.length ? base64Lookup[code] : undefined;
+      if (decoded === undefined || decoded === 255) throw new TypeError("Invalid base64 spectrum frame");
+      sextets[offset] = decoded;
+    }
+    const packed = ((sextets[0] ?? 0) << 18) | ((sextets[1] ?? 0) << 12)
+      | ((sextets[2] ?? 0) << 6) | (sextets[3] ?? 0);
+    if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed >> 16 & 0xff;
+    if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed >> 8 & 0xff;
+    if (outputIndex < outputLength) spectrumBinBuffer[outputIndex++] = packed & 0xff;
+  }
+  return spectrumBinBuffer;
+}
+
+let nthScratch = new Float64Array(0);
+
+export function nthElement(values: NumericBins, target: number): number | null {
+  if (values.length === 0 || target < 0 || target >= values.length) return null;
+  if (nthScratch.length < values.length) nthScratch = new Float64Array(values.length);
+  for (let index = 0; index < values.length; index += 1) nthScratch[index] = values[index] ?? 0;
+  let low = 0;
+  let high = values.length - 1;
+  while (low < high) {
+    const pivot = nthScratch[low + ((high - low) >> 1)] ?? 0;
+    let left = low;
+    let right = high;
+    while (left <= right) {
+      while ((nthScratch[left] ?? Infinity) < pivot) left += 1;
+      while ((nthScratch[right] ?? -Infinity) > pivot) right -= 1;
+      if (left <= right) {
+        const temporary = nthScratch[left] ?? 0;
+        nthScratch[left] = nthScratch[right] ?? 0;
+        nthScratch[right] = temporary;
+        left += 1;
+        right -= 1;
+      }
+    }
+    if (right < target) low = left;
+    if (target < left) high = right;
+  }
+  return nthScratch[target] ?? null;
+}
+
+export function estimateNoiseFloorDb(bins: unknown): number | null {
+  if (!isNumericBins(bins) || bins.length === 0) return null;
+  return nthElement(bins, Math.floor(bins.length * 0.15));
+}

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/spectrum-math.test.mjs

@@ -0,0 +1,51 @@
+// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+import assert from "node:assert/strict";
+import test from "node:test";
+import vm from "node:vm";
+import { build } from "esbuild";
+
+async function loadSpectrumMath() {
+  const result = await build({
+    entryPoints: [new URL("../src/features/spectrum/math.ts", import.meta.url).pathname],
+    bundle: true,
+    format: "cjs",
+    platform: "browser",
+    target: "es2022",
+    write: false,
+  });
+  const module = { exports: {} };
+  vm.runInNewContext(result.outputFiles[0].text, {
+    module,
+    exports: module.exports,
+    Array,
+    ArrayBuffer,
+    DataView,
+    Float32Array,
+    Float64Array,
+    Int8Array,
+    Uint8Array,
+    Number,
+    Math,
+    TypeError,
+  });
+  return module.exports;
+}
+
+test("compact spectrum frames decode signed i8 bins", async () => {
+  const { decodeBase64Int8 } = await loadSpectrumMath();
+  const bins = decodeBase64Int8("/4AAfw==");
+  assert.deepEqual(Array.from(bins), [-1, -128, 0, 127]);
+  assert.throws(() => decodeBase64Int8("%%%"), /Invalid base64/);
+});
+
+test("noise floor uses the lower spectrum percentile without sorting input", async () => {
+  const { estimateNoiseFloorDb } = await loadSpectrumMath();
+  const bins = new Float32Array([-70, -100, -95, -90, -80, -85, -75]);
+  const original = Array.from(bins);
+  assert.equal(estimateNoiseFloorDb(bins), -95);
+  assert.deepEqual(Array.from(bins), original);
+  assert.equal(estimateNoiseFloorDb(new Float32Array()), null);
+});