[WIP] feat(examples): AssemblyScript implementation of median algorithm

examples/Makefile

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+
+.PHONY: all clean
+
+all:
+	make -C as-median build
+
+clean:
+	make -C as-median $@

examples/as-median/.gitignore

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+/build
+/node_modules

examples/as-median/Makefile

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+
+.PHONY: build clean
+
+build:
+	npm run asbuild
+
+clean:
+	rm -f build/*.wasm
+	rm -f build/*.wasm.map
+	rm -f build/*.wat

examples/as-median/asconfig.json

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+{
+  "targets": {
+    "debug": {
+      "binaryFile": "build/untouched.wasm",
+      "textFile": "build/untouched.wat",
+      "sourceMap": true,
+      "debug": true
+    },
+    "release": {
+      "binaryFile": "build/optimized.wasm",
+      "textFile": "build/optimized.wat",
+      "sourceMap": true,
+      "optimizeLevel": 3,
+      "shrinkLevel": 0,
+      "converge": false,
+      "noAssert": false
+    }
+  },
+  "options": {}
+}

examples/as-median/assembly/index.ts

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+
+import { JSONEncoder } from "assemblyscript-json"
+import { parse, Arr, Integer, Value } from "assemblyscript-json/JSON";
+
+export function exec(msg: usize, msg_size: usize, out_ptr: usize, out_size: usize): i32 {
+
+	/* load input buffer into array */
+	let in_buf = new Uint8Array(msg_size as i32);
+	for(let i: usize = 0; i < msg_size; i++) {
+	    let byte = load<u8>(msg + i);
+	    in_buf[i as i32] = byte;
+	}
+
+	/* parse input buffer into an Array<i32> */
+	let arr = parse(in_buf) as Arr;
+	let value_array = arr.valueOf() as Array<Value>;
+	let len = value_array.length;
+	let sample = new Array<i32>(len);
+	for(let i = 0; i < len; i++) {
+		let entry = value_array[i] as Integer;
+		sample[i] = entry.valueOf() as i32;
+	}
+
+	let median = calc_median(len, sample);
+
+	/* encode JSON object */
+	let encoder = new JSONEncoder();
+	encoder.pushObject(null);
+	encoder.setFloat("median", median);
+	encoder.popObject();
+
+	/* get pointer to buffer address */
+	let out_buf = encoder.serialize().buffer;
+	let out_buf_len = out_buf.byteLength;
+	let out_buf_ptr = memory.data(8);
+	store<ArrayBuffer>(out_buf_ptr, out_buf);
+	store<usize>(out_ptr, out_buf_ptr);
+
+	/* get pointer to buffer's size address */
+	let out_size_ptr = memory.data(32);
+	store<i32>(out_size_ptr, out_buf_len);
+	store<usize>(out_size, out_size_ptr);
+
+	return 0
+}
+
+/* recall that a median can have a fractional part */
+function calc_median(len: usize, val: Array<i32>): f64 {
+	val.sort();
+
+	/*
+	 * In the following, `lmid` and `rmid` are the same whenever `val` has
+	 * odd length. Note also that the average of 2 identical values is
+	 * simply the value itself.
+	 */
+	let lmid = calc_mid(len, 0) as i32;
+	let rmid = calc_mid(len, 1) as i32;
+
+
+	/* calculate aforementioned average by leveraging distributivity */
+	let lhalf = (val[lmid] as f64) / 2.0;
+	let rhalf = (val[rmid] as f64) / 2.0;
+	let median = lhalf + rhalf;
+
+	return median
+}
+
+function calc_mid(len: usize, rhs: bool): usize {
+	/*
+	 * Compute the index of the order statistic corresponding to the median
+	 * if the former exists.  Otherwise, return a choice of one of the two
+	 * closest order statistics.
+	 */
+	if (len % 2 == 0) {
+		if (rhs) {
+			let rmid = len / 2 + 1;
+			return rmid;
+		} else {
+			let lmid = len / 2;
+			return lmid;
+		}
+	} else {
+		let mid = (len + 1) / 2;
+		return mid;
+	}
+}

examples/as-median/assembly/tsconfig.json

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+{
+  "extends": "assemblyscript/std/assembly.json",
+  "include": [
+    "./**/*.ts"
+  ]
+}

examples/as-median/index.js

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+const fs = require("fs");
+const loader = require("@assemblyscript/loader/umd");
+const imports = { /* imports go here */ };
+const wasmModule = loader.instantiateSync(fs.readFileSync(__dirname + "/build/optimized.wasm"), imports);
+module.exports = wasmModule.exports;

examples/as-median/package.json

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+{
+  "name": "as-median",
+  "version": "0.0.0",
+  "description": "Calculate median of a dataset",
+  "main": "index.js",
+  "scripts": {
+    "test": "node tests",
+    "asbuild:untouched": "asc assembly/index.ts --target debug",
+    "asbuild:optimized": "asc assembly/index.ts --target release",
+    "asbuild": "npm run asbuild:untouched && npm run asbuild:optimized"
+  },
+  "author": "ntls.io",
+  "license": "Apache-2.0",
+  "dependencies": {
+    "@assemblyscript/loader": "^0.19.22",
+    "assemblyscript-json": "^1.1.0"
+  },
+  "devDependencies": {
+    "assemblyscript": "^0.19.22"
+  }
+}