JitterRng: port PR dhardy#63 to fix on Windows

dhardy#63

src/jitter.rs

@@ -654,7 +654,7 @@ impl JitterRng {
     }
 }
 
-#[cfg(not(any(target_os = "macos", target_os = "ios")))]
+#[cfg(not(any(target_os = "macos", target_os = "ios", target_os = "windows")))]
 fn get_nstime() -> u64 {
     use std::time::{SystemTime, UNIX_EPOCH};
 
@@ -678,6 +678,21 @@ fn get_nstime() -> u64 {
     unsafe { libc::mach_absolute_time() }
 }
 
+#[cfg(target_os = "windows")]
+fn get_nstime() -> u64 {
+    #[allow(non_camel_case_types)]
+    type LARGE_INTEGER = i64;
+    #[allow(non_camel_case_types)]
+    type BOOL = i32;
+    extern "system" {
+        fn QueryPerformanceCounter(lpPerformanceCount: *mut LARGE_INTEGER) -> BOOL;
+    }
+
+    let mut t = 0;
+    unsafe { QueryPerformanceCounter(&mut t); }
+    t as u64
+}
+
 // A function that is opaque to the optimizer to assist in avoiding dead-code
 // elimination. Taken from `bencher`.
 fn black_box<T>(dummy: T) -> T {