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// Part of the Wasmtime Project, under the Apache License v2.0 with LLVM
// Exceptions. See
// https://github.com/bytecodealliance/wasmtime/blob/main/LICENSE for license
// information.
//
// Significant parts of this file are derived from cloudabi-utils. See
// https://github.com/bytecodealliance/wasmtime/blob/main/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 "ssp_config.h"
#include "bh_platform.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
#ifndef BH_PLATFORM_LINUX_SGX
#include <sys/random.h>
#endif
void
random_buf(void *buf, size_t len)
{
for (;;) {
ssize_t x = getrandom(buf, len, 0);
if (x < 0) {
if (errno == EINTR)
continue;
os_printf("getrandom failed: %s", strerror(errno));
abort();
}
if ((size_t)x == len)
return;
buf = (void *)((unsigned char *)buf + x);
len -= (size_t)x;
}
}
#else
static int urandom;
static void
open_urandom(void)
{
urandom = open("/dev/urandom", O_RDONLY);
if (urandom < 0) {
os_printf("Failed to open /dev/urandom\n");
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 ((size_t)read(urandom, buf, len) != len) {
os_printf("Short read on /dev/urandom\n");
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;
}
}
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