Add an option to select how to seed random()

cli/asc.js

@@ -24,6 +24,7 @@ const mkdirp = require("./util/mkdirp");
 const find = require("./util/find");
 const EOL = process.platform === "win32" ? "\r\n" : "\n";
 const SEP = process.platform === "win32" ? "\\" : "/";
+const Long = require("long");
 const binaryen = global.Binaryen || (global.Binaryen = require("binaryen"));
 
 // Proxy Binaryen's ready event
@@ -238,6 +239,43 @@ exports.main = function main(argv, options, callback) {
   assemblyscript.setGlobalAlias(compilerOptions, "abort", "~lib/builtins/abort");
   assemblyscript.setGlobalAlias(compilerOptions, "trace", "~lib/builtins/trace");
 
+  // Initialize randomness source
+  switch (args.seedRandom) {
+    case "const": {
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_CONST", "1");
+      // fall-through
+    }
+    case undefined: {
+      let value = Long.fromBits(Math.random() * 0xffffffff, Math.random() * 0xffffffff, true);
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_LOW", (value.low >>> 0).toString());
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_HIGH", (value.high >>> 0).toString());
+      break;
+    }
+    case "math": {
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_MATH", "1");
+      break;
+    }
+    case "date": {
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_DATE", "1");
+      break;
+    }
+    case "wasi": {
+      assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_WASI", "1");
+      break;
+    }
+    default: {
+      if (/^\d+$/.test(args.seedRandom)) {
+        let value = Long.fromString(args.seedRandom);
+        assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_CONST", "1");
+        assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_LOW", (value.low >>> 0).toString());
+        assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_HIGH", (value.high >>> 0).toString());
+      } else {
+        assemblyscript.setGlobalAlias(compilerOptions, "ASC_SEEDRANDOM_FUNC", String(args.seedRandom));
+      }
+      break;
+    }
+  }
+
   // Add or override aliases if specified
   if (args.use) {
     let aliases = args.use;

cli/asc.json

@@ -191,6 +191,22 @@
     "type": "S",
     "alias": "u"
   },
+  "seedRandom": {
+    "category": "Features",
+    "description": [
+      "Sets the randomness source used by Math.random. Defalts to",
+      "a compile-time constant while emitting a warning.",
+      "",
+      " const     Compile-time constant without a warning.",
+      " 12345     Custom constant without a warning.",
+      " date      Imports 'Date' from JS and calls Date.now()",
+      " math      Imports 'Math' from JS and calls Math.random()",
+      " wasi      Uses the respective WASI interface.",
+      " ...       Internal name of a custom function returning i64.",
+      ""
+    ],
+    "type": "s"
+  },
 
   "memoryBase": {
     "category": "Linking",

std/assembly/math.ts

@@ -1,4 +1,10 @@
+/// <reference path="./util/seedrandom.d.ts" />
+
+import { ArrayBufferView } from "./arraybuffer";
 import * as JSMath from "./bindings/Math";
+import * as JSDate from "./bindings/Date";
+import * as wasi from "./bindings/wasi_snapshot";
+
 export { JSMath };
 
 import {
@@ -135,7 +141,7 @@ function umuldi(u: u64, v: u64): u64 {
 
 /** @internal */
 function pio2_large_quot(x: f64, u: i64): i32 { // see: jdh8/metallic/blob/master/src/math/double/rem_pio2.c
-  const bits = PIO2_TABLE.dataStart;
+  const bits = changetype<ArrayBufferView>(PIO2_TABLE).dataStart;
 
   var magnitude = u & 0x7FFFFFFFFFFFFFFF;
   var offset = (magnitude >> 52) - 1045;
@@ -1410,7 +1416,7 @@ export namespace NativeMath {
   }
 
   export function random(): f64 { // see: v8/src/base/utils/random-number-generator.cc
-    if (!random_seeded) throw new Error("PRNG must be seeded.");
+    if (!random_seeded) seedRandom(seedRandomSelect());
     var s1 = random_state0_64;
     var s0 = random_state1_64;
     random_state0_64 = s0;
@@ -1782,7 +1788,7 @@ function expo2f(x: f32): f32 { // exp(x)/2 for x >= log(DBL_MAX)
 @inline
 function pio2f_large_quot(x: f32, u: i32): i32 { // see: jdh8/metallic/blob/master/src/math/float/rem_pio2f.c
   const coeff = reinterpret<f64>(0x3BF921FB54442D18); // π * 0x1p-65 = 8.51530395021638647334e-20
-  const bits = PIO2F_TABLE.dataStart;
+  const bits = changetype<ArrayBufferView>(PIO2F_TABLE).dataStart;
 
   var offset = (u >> 23) - 152;
   var shift  = <u64>(offset & 63);
@@ -2603,7 +2609,7 @@ export namespace NativeMathf {
 
   // Using xoroshiro64starstar from http://xoshiro.di.unimi.it/xoroshiro64starstar.c
   export function random(): f32 {
-    if (!random_seeded) throw new Error("PRNG must be seeded.");
+    if (!random_seeded) NativeMath.seedRandom(seedRandomSelect());
 
     var s0 = random_state0_32;
     var s1 = random_state1_32;
@@ -3132,3 +3138,30 @@ export function ipow64f(x: f64, e: i32): f64 {
   }
   return sign ? 1.0 / out : out;
 }
+
+// @ts-ignore: decorator
+@lazy
+const seedRandomSelect_wasiBuf: i64[] = [ 0 ];
+
+function seedRandomSelect(): i64 {
+  if (isDefined(ASC_SEEDRANDOM_FUNC)) return ASC_SEEDRANDOM_FUNC();
+  if (isDefined(ASC_SEEDRANDOM_MATH)) {
+    let val: i64;
+    do val = reinterpret<i64>(JSMath.random());
+    while (!val);
+    return val;
+  }
+  if (isDefined(ASC_SEEDRANDOM_DATE)) return <i64>JSDate.now();
+  if (isDefined(ASC_SEEDRANDOM_WASI)) {
+    let buf = changetype<ArrayBufferView>(seedRandomSelect_wasiBuf).dataStart;
+    let val: i64;
+    do assert(wasi.random_get(buf, 8) == wasi.errno.SUCCESS);
+    while (!(val = load<i64>(buf)));
+    return val;
+  }
+  if (!isDefined(ASC_SEEDRANDOM_CONST)) {
+    WARNING("Falling back to a compile-time constant random seed. See --seedRandom to silence this warning.");
+  }
+  const value = ((<i64>ASC_SEEDRANDOM_HIGH) << 32) | <i64><u32>ASC_SEEDRANDOM_LOW;
+  return value;
+}

std/assembly/util/seedrandom.d.ts

@@ -0,0 +1,7 @@
+declare const ASC_SEEDRANDOM_LOW: i32;
+declare const ASC_SEEDRANDOM_HIGH: i32;
+declare const ASC_SEEDRANDOM_CONST: i32;
+declare const ASC_SEEDRANDOM_DATE: i32;
+declare const ASC_SEEDRANDOM_MATH: i32;
+declare const ASC_SEEDRANDOM_WASI: i32;
+declare const ASC_SEEDRANDOM_FUNC: i32;

tests/compiler/std/array.json

@@ -2,6 +2,7 @@
   "asc_flags": [
     "--runtime half",
     "--explicitStart",
+    "--seedRandom math",
     "--use ASC_RTRACE=1"
   ]
 }