On Fri, 2018-03-09 at 23:33 +0100, Stephen Kitt wrote: > +/* > + * SCSI command sizes are as follows, in bytes, for fixed size commands, per > + * group: 6, 10, 10, 12, 16, 12, 10, 10. The top three bits of an opcode > + * determine its group. > + * The size table is encoded into a 32-bit value by subtracting each value > + * from 16, resulting in a value of 1715488362 > + * (6 << 28 + 6 << 24 + 4 << 20 + 0 << 16 + 4 << 12 + 6 << 8 + 6 << 4 + 10). > + * Command group 3 is reserved and should never be used. > + */ > +#define COMMAND_SIZE(opcode) \ > + (16 - (15 & (1715488362 >> (4 * (((opcode) >> 5) & 7))))) To me this seems hard to read and hard to verify. Could this have been written as a combination of ternary expressions, e.g. using a gcc statement expression to ensure that opcode is evaluated once? Thanks, Bart.
