about the hid report descriptor

Hi,everyone
Does the report dexcriptor support negative value.i have checked the keil usb demo of hitex board,the report descriptor is declared as unsigned char.
one more question,in the get_descriptor function,
case USB_CONFIGURATION_DESCRIPTOR_TYPE: pD = (BYTE *)USB_ConfigDescriptor; for (n = 0; n != SetupPacket.wValue.WB.L; n++) { if (((USB_CONFIGURATION_DESCRIPTOR *)pD)->bLength != 0) { pD += ((USB_CONFIGURATION_DESCRIPTOR *)pD)->wTotalLength; } }
what is the wValue.WB.L in the configDescriptor indicate?Why here use the wTotalLength.Thanks!