Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/wasi-c/sandboxed-system-primitives/src/random.c

@@ -0,0 +1,92 @@
+// Part of the Wasmtime Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://github.com/CraneStation/wasmtime/blob/master/LICENSE for license information.
+//
+// Significant parts of this file are derived from cloudabi-utils. See
+// https://github.com/CraneStation/wasmtime/blob/master/lib/wasi/sandboxed-system-primitives/src/LICENSE
+// for license information.
+//
+// The upstream file contains the following copyright notice:
+//
+// Copyright (c) 2016 Nuxi, https://nuxi.nl/
+
+#include "config.h"
+
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "random.h"
+
+#if CONFIG_HAS_ARC4RANDOM_BUF
+
+void random_buf(void *buf, size_t len) {
+  arc4random_buf(buf, len);
+}
+
+#elif CONFIG_HAS_GETRANDOM
+
+#include <sys/random.h>
+
+void random_buf(void *buf, size_t len) {
+  for (;;) {
+     ssize_t x = getrandom(buf, len, 0);
+     if (x < 0) {
+         if (errno == EINTR)
+             continue;
+         fprintf(stderr, "getrandom failed: %s", strerror(errno));
+         abort();
+     }
+     if (x == len)
+         return;
+     buf = (void *)((unsigned char *)buf + x);
+     len -= x;
+  }
+}
+
+#else
+
+static int urandom;
+
+static void open_urandom(void) {
+  urandom = open("/dev/urandom", O_RDONLY);
+  if (urandom < 0) {
+    fputs("Failed to open /dev/urandom\n", stderr);
+    abort();
+  }
+}
+
+void random_buf(void *buf, size_t len) {
+  static pthread_once_t open_once = PTHREAD_ONCE_INIT;
+  pthread_once(&open_once, open_urandom);
+
+  if (read(urandom, buf, len) != len) {
+    fputs("Short read on /dev/urandom\n", stderr);
+    abort();
+  }
+}
+
+#endif
+
+// Calculates a random number within the range [0, upper - 1] without
+// any modulo bias.
+//
+// The function below repeatedly obtains a random number from
+// arc4random() until it lies within the range [2^k % upper, 2^k). As
+// this range has length k * upper, we can safely obtain a number
+// without any modulo bias.
+uintmax_t random_uniform(uintmax_t upper) {
+  // Compute 2^k % upper
+  //      == (2^k - upper) % upper
+  //      == -upper % upper.
+  uintmax_t lower = -upper % upper;
+  for (;;) {
+    uintmax_t value;
+    random_buf(&value, sizeof(value));
+    if (value >= lower)
+      return value % upper;
+  }
+}