std: rand: Use BCrypt on UWP

As Rtl* functions are not allowed there

src/libstd/build.rs

@@ -41,6 +41,8 @@ fn main() {
         println!("cargo:rustc-link-lib=resolv");
     } else if target.contains("uwp") {
         println!("cargo:rustc-link-lib=ws2_32");
+        // For BCryptGenRandom
+        println!("cargo:rustc-link-lib=bcrypt");
     } else if target.contains("windows") {
         println!("cargo:rustc-link-lib=advapi32");
         println!("cargo:rustc-link-lib=ws2_32");

src/libstd/sys/windows/c.rs

@@ -4,6 +4,10 @@
 #![cfg_attr(test, allow(dead_code))]
 #![unstable(issue = "0", feature = "windows_c")]
 
+macro_rules! ifdef {
+    ($($t:tt)*) => ($($t)*)
+}
+
 use crate::os::raw::{c_int, c_uint, c_ulong, c_long, c_longlong, c_ushort, c_char};
 use crate::ptr;
 
@@ -655,6 +659,27 @@ pub struct timeval {
     pub tv_usec: c_long,
 }
 
+// Functions forbidden when targeting UWP
+#[cfg(not(target_vendor = "uwp"))]
+ifdef! {
+    extern "system" {
+        #[link_name = "SystemFunction036"]
+        pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
+    }
+}
+
+// UWP specific functions & types
+#[cfg(target_vendor = "uwp")]
+ifdef! {
+    pub const BCRYPT_USE_SYSTEM_PREFERRED_RNG: DWORD = 0x00000002;
+
+    extern "system" {
+        pub fn BCryptGenRandom(hAlgorithm: LPVOID, pBuffer: *mut u8,
+                               cbBuffer: ULONG, dwFlags: ULONG) -> LONG;
+    }
+}
+
+// Shared between Desktop & UWP
 extern "system" {
     pub fn WSAStartup(wVersionRequested: WORD,
                       lpWSAData: LPWSADATA) -> c_int;
@@ -950,8 +975,6 @@ extern "system" {
                   exceptfds: *mut fd_set,
                   timeout: *const timeval) -> c_int;
 
-    #[link_name = "SystemFunction036"]
-    pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
 
     pub fn GetProcessHeap() -> HANDLE;
     pub fn HeapAlloc(hHeap: HANDLE, dwFlags: DWORD, dwBytes: SIZE_T) -> LPVOID;

src/libstd/sys/windows/rand.rs

@@ -2,6 +2,7 @@ use crate::io;
 use crate::mem;
 use crate::sys::c;
 
+#[cfg(not(target_vendor = "uwp"))]
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut v = (0, 0);
     let ret = unsafe {
@@ -14,3 +15,20 @@ pub fn hashmap_random_keys() -> (u64, u64) {
     }
     return v
 }
+
+#[cfg(target_vendor = "uwp")]
+pub fn hashmap_random_keys() -> (u64, u64) {
+    use crate::ptr;
+
+    let mut v = (0, 0);
+    let ret = unsafe {
+        c::BCryptGenRandom(ptr::null_mut(), &mut v as *mut _ as *mut u8,
+                           mem::size_of_val(&v) as c::ULONG,
+                           c::BCRYPT_USE_SYSTEM_PREFERRED_RNG)
+    };
+    if ret != 0 {
+        panic!("couldn't generate random bytes: {}",
+               io::Error::last_os_error());
+    }
+    return v
+}