g^510 and g^511

[fcorneli]

When I calculate g^510 and g^511 manually, I get values 1 and 3. Why does the EXP table contain values 0 and 0 here?

shamir/src/main/java/com/codahale/shamir/GF256.java

Line 146 in 58b9502

(byte) 0x24, (byte) 0x6c, (byte) 0xb4, (byte) 0xc7, (byte) 0x52, (byte) 0xf6, (byte) 0x00,

[codahale]

Those are never actually referenced, since EXP only extends to 255+255.

This table was generated using the procedure specified here: https://github.com/rsc/qr/blob/master/gf256/gf256.go#L21

[fcorneli]

Sure that g^510 is not required for 255+255?

[codahale]

https://github.com/codahale/shamir/blob/master/src/main/java/com/codahale/shamir/GF256.java#L158-L160

[fcorneli]

Put g^510 and g^511 there and you can kick out an ifin mul... no?

[codahale]

You’re missing the point — it’s a lookup table for the results of everything except a=0 or b=0, so it only needs to be 510 elements long. Please stop opening issues unless you can write a test demonstrating a problem with the code.