Support AIX operating system (#123)

The physical CPU number detection is done by dividing logical CPU number
with SMT mode.

src/lib.rs

@@ -110,7 +110,12 @@ pub fn get_physical() -> usize {
 }
 
 
-#[cfg(not(any(target_os = "linux", target_os = "windows", target_os="macos", target_os="openbsd")))]
+#[cfg(not(any(
+    target_os = "linux",
+    target_os = "windows",
+    target_os = "macos",
+    target_os = "openbsd",
+    target_os = "aix")))]
 #[inline]
 fn get_num_physical_cpus() -> usize {
     // Not implemented, fall back
@@ -327,11 +332,31 @@ fn get_num_physical_cpus() -> usize {
     cpus as usize
 }
 
+#[cfg(target_os = "aix")]
+fn get_num_physical_cpus() -> usize {
+    match get_smt_threads_aix() {
+        Some(num) => get_num_cpus() / num,
+        None => get_num_cpus(),
+    }
+}
+
+#[cfg(target_os = "aix")]
+fn get_smt_threads_aix() -> Option<usize> {
+    let smt = unsafe {
+        libc::getsystemcfg(libc::SC_SMT_TC)
+    };
+    if smt == u64::MAX {
+        return None;
+    }
+    Some(smt as usize)
+}
+
 #[cfg(any(
     target_os = "nacl",
     target_os = "macos",
     target_os = "ios",
     target_os = "android",
+    target_os = "aix",
     target_os = "solaris",
     target_os = "illumos",
     target_os = "fuchsia")
@@ -413,6 +438,7 @@ fn get_num_cpus() -> usize {
     target_os = "macos",
     target_os = "ios",
     target_os = "android",
+    target_os = "aix",
     target_os = "solaris",
     target_os = "illumos",
     target_os = "fuchsia",