audio-player: decoding optimised, not using typed arrays

cmd/audio-player/adpcm.js

@@ -31,7 +31,6 @@ let est = 0, // Estimation of sample based on quantised ADPCM nibble.
 	step = 0;
 
 function decodeSample(nibble) {
-
 	let diff = 0;
 	if ((nibble & 4) != 0) {
 		diff += step;
@@ -58,46 +57,41 @@ function decodeSample(nibble) {
 
 	step = stepTable[idx];
 
-	result = new Uint8Array(new Uint16Array([est]).buffer);
+	result = est;
 	return result;
 }
 
 function decode(b) {
-	// b should be a Uint8Array
-	if (!(b instanceof Uint8Array)) {
-		console.log("Error: data is not a Uint8Array");
-		return;
-	}
-
 	// Initialize Decoder with first 4 bytes of b.
-	est = (new Uint16Array(b.slice(0, 2).buffer))[0];
+	est = bytesToInt16(b[0], b[1]);
 	idx = b[byteDepth];
 	step = stepTable[idx];
 
-	var result = new Uint8Array(b.slice(0, 2));
+	var result = b.slice(0, 2);
 
 	for (var i = headBytes; i < b.length - b[3]; i++) {
 		var twoNibs = b[i];
 		var nib2 = twoNibs >> 4;
 		var nib1 = (nib2 << 4) ^ twoNibs
-		var firstBytes = decodeSample(nib1)
-		result = concat(result, firstBytes)
 
-		var secondBytes = decodeSample(nib2)
-		result = concat(result, secondBytes)
+		var sample1 = int16ToBytes(decodeSample(nib1))
+		result.push(...sample1)
+
+		var sample2 = int16ToBytes(decodeSample(nib2))
+		result.push(...sample2)
 	}
 	if (b[3] == 1) {
 		var padNib = b[b.length - 1]
-		var samp = decodeSample(padNib)
-		result = concat(result, samp)
+		var sample = int16ToBytes(decodeSample(padNib))
+		result.push(...sample)
 	}
 	return result;
 }
 
-// concat concatenates TypedArrays a and b of same type.
-function concat(a, b) {
-	var c = new(a.constructor)(a.length + b.length);
-	c.set(a, 0);
-	c.set(b, a.length);
-	return c;
+function int16ToBytes(num) {
+	return [(num & 0x00ff), (num & 0xff00) >> 8];
+}
+
+function bytesToInt16(b) {
+	return (b[0] | (b[1] << 8))
 }

cmd/audio-player/main.js

@@ -7,7 +7,7 @@ window.onload = function () {
         reader.onload = event => {
             bytes = new Uint8Array(event.target.result)
 
-            var decoded = decode(bytes)
+            var decoded = decode(Array.from(bytes))
 
             console.log("playing file")
             var player = new PCMPlayer({
@@ -16,7 +16,7 @@ window.onload = function () {
                 sampleRate: 48000,
                 flushingTime: 2000
             });
-            player.feed(decoded)
+            player.feed(Uint8Array.from(decoded))
         }
         reader.onerror = error => reject(error)
         reader.readAsArrayBuffer(input)