[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/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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+
+export function alloc(count: i32): usize {
+	/* allocate memory buffer */
+	let buf = new Array<i32>(count);
+	let buf_ptr = memory.data(32);
+
+	/*
+	 * dereference a pointer and mutate
+	 * its underlying value
+	 */
+	store<Array<i32>>(buf_ptr, buf);
+
+	return buf_ptr
+}
+
+// note that a median can have a fractional part
+export function exec(msg: usize, msg_len: usize, out_ptr: usize, out_size: usize): i32 {
+	/* error if msg size is not a multiple of 32 in bits */
+	if (msg_len % 4 != 0) { return -1 }
+	let count = msg_len / 4;
+	let val = new Array<i32>(count as i32);
+
+	/* convert length to bits from octets */
+	let len = (msg_len * 8) as i32;
+
+	for(let i = 0; i < len; i++) {
+		val[i] = load<i32>(msg + (i * 32));
+	}
+	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 that value.
+	 */
+	let lmid = calc_mid(msg_len, 0);
+	let rmid = calc_mid(msg_len, 1);
+
+	let sum = (val[lmid as i32] + val[rmid as i32]) as f64;
+	let median = sum / 2.0;
+
+	/* create and populate the output buffer */
+	out_size = 64 / 8;
+	out_ptr = memory.data(64);
+	store<f64>(out_ptr, median);
+
+	return 0
+}
+
+function calc_mid(len: usize, rhs: bool): usize {
+	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/build/.gitignore

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+*.wasm
+*.wasm.map
+*.asm.js

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"
+  },
+  "devDependencies": {
+    "assemblyscript": "^0.19.22"
+  }
+}