Correct the logic to return device count.

We were not handling the cases where a device identifier
does not provide a backend or a device type. Changed the logic
to count all devices of a given type if no backend is specified.
Similarly, all devices in a backend are counted if no device
type is provided.

Author: Diptorup Deb

dpctl-capi/source/dpctl_sycl_device_manager.cpp

@@ -224,6 +224,22 @@ size_t DPCTLDeviceMgr_GetNumDevices(int device_identifier)
 {
     size_t nDevices = 0;
     auto &cache = DeviceCacheBuilder::getDeviceCache();
+
+    // If the identifier is 0 (UNKNOWN_DEVICE) return 0.
+    if (!device_identifier)
+        return 0;
+
+    // Check if the device identifier has a backend specified. If not, then
+    // make sure we match with all backends. The lower 6 bits are for the
+    // device types, so we blank out those bits to check if any of the
+    // higher bits reserved for the backend types was non-zero.
+    if (!((device_identifier & DPCTL_ALL_BACKENDS) >> 6))
+        device_identifier |= DPCTL_ALL_BACKENDS;
+
+    // Check if a device type was specified. If not, set device type to ALL.
+    if (!(device_identifier & ~DPCTL_ALL_BACKENDS))
+        device_identifier |= DPCTL_ALL;
+
     for (const auto &entry : cache) {
         auto Bty(DPCTL_SyclBackendToDPCTLBackendType(
             entry.first.get_platform().get_backend()));