Remove raw-cpuid dependency and use rdrand intrinsics

Cargo.toml

@@ -34,9 +34,6 @@ array-init = "0.0.4"
 version = "0.2.2"
 default-features = false
 
-[target.'cfg(target_arch = "x86_64")'.dependencies]
-raw-cpuid = "6.1.0"
-
 [dependencies.ux]
 default-features = false
 version = "0.1.3"

src/instructions/random.rs

@@ -8,64 +8,77 @@ pub struct RdRand(());
 impl RdRand {
     /// Creates Some(RdRand) if RDRAND is supported, None otherwise
     pub fn new() -> Option<Self> {
-        let cpuid = raw_cpuid::CpuId::new();
-        let has_rdrand = match cpuid.get_feature_info() {
-            Some(finfo) => finfo.has_rdrand(),
-            None => false,
-        };
-
-        match has_rdrand {
-            true => Some(RdRand(())),
-            false => None,
+        // RDRAND support indicated by CPUID page 01h, ecx bit 30
+        // https://en.wikipedia.org/wiki/RdRand#Overview
+        let cpuid = unsafe { core::arch::x86_64::__cpuid(0x1) };
+        if cpuid.ecx & (1 << 30) != 0 {
+            Some(RdRand(()))
+        } else {
+            None
         }
     }
 
     /// Uniformly sampled u64.
     /// May fail in rare circumstances or heavy load.
     #[inline]
     pub fn get_u64(&self) -> Option<u64> {
-        let res: u64;
-        let ok: u8;
+        let mut res: u64 = 0;
         unsafe {
-            asm!("rdrand %rax; setc $1;"
-                : "={rax}"(res) "=r"(ok)
-                :: "flags" : "volatile");
-        }
-        match ok {
-            1 => Some(res),
-            _ => None,
+            match core::arch::x86_64::_rdrand64_step(&mut res) {
+                1 => Some(res),
+                x => {
+                    debug_assert_eq!(x, 0, "rdrand64 returned non-binary value");
+                    None
+                }
+            }
         }
     }
     /// Uniformly sampled u32.
     /// May fail in rare circumstances or heavy load.
     #[inline]
     pub fn get_u32(&self) -> Option<u32> {
-        let res: u32;
-        let ok: u8;
+        let mut res: u32 = 0;
         unsafe {
-            asm!("rdrand %eax; setc $1;"
-                : "={eax}"(res) "=r"(ok)
-                :: "flags" : "volatile");
-        }
-        match ok {
-            1 => Some(res),
-            _ => None,
+            match core::arch::x86_64::_rdrand32_step(&mut res) {
+                1 => Some(res),
+                x => {
+                    debug_assert_eq!(x, 0, "rdrand32 returned non-binary value");
+                    None
+                }
+            }
         }
     }
     /// Uniformly sampled u16.
     /// May fail in rare circumstances or heavy load.
     #[inline]
     pub fn get_u16(&self) -> Option<u16> {
-        let res: u16;
-        let ok: u8;
+        let mut res: u16 = 0;
         unsafe {
-            asm!("rdrand %ax; setc $1;"
-                : "={ax}"(res) "=r"(ok)
-                :: "flags" : "volatile");
+            match core::arch::x86_64::_rdrand16_step(&mut res) {
+                1 => Some(res),
+                x => {
+                    debug_assert_eq!(x, 0, "rdrand16 returned non-binary value");
+                    None
+                }
+            }
         }
-        match ok {
-            1 => Some(res),
-            _ => None,
+    }
+}
+
+#[cfg(all(test, target_arch = "x86_64"))]
+mod tests {
+    use super::*;
+
+    #[test]
+    pub fn test_rdrand() {
+        let rand = RdRand::new();
+        if is_x86_feature_detected!("rdrand") {
+            let rand = rand.unwrap();
+            assert!(rand.get_u16().is_some());
+            assert!(rand.get_u32().is_some());
+            assert!(rand.get_u64().is_some());
+        } else {
+            assert!(rand.is_none());
         }
     }
 }