On Tue, 17 Oct 2017 07:36:42 +1100, "Tobin C. Harding" said:
Jason A. Donenfeld suggested (offered to) add a helper function in siphash, along the lines of siphash_1u() but we still need to know the exact size of the return value (so we can drop half of it if it is 64 bits). We just want a 32 bit identifier returned after hashing the address.
Why is truncating to 32 bits needed? Just either use a 32/64 bit value as appropriate for the architecture, or just declare "This is 32 bits regardless" or "this is 64 regardless". What problem are you trying to solve by hashing addresses? (Hint - the two in-kernel users of siphash are net/core/secure_seq.c and net/ipv4/syncookies.c, both of which know how big the hashed value has to be, and the size isn't architecture dependent as it's fixed by the size of a protocol header field)