Error comment on bit twiddling trick

[Kingfish404]

SpectrePoC/spectre.c

Line 193 in 2a01f86

x = (x | (x >> 16)); /* Set x=-1 if j&6=0, else x=0 */

should be

/* Set x=0xFFFFFFFFFFFFFFFF if x=0xFFFFFFFFFFFF0000, else x=0 */
// or
/* Set x=-1 if j%6=0, else x=0 */ 

It's clearly that the 2's complement of -1 is 0xFFFFFFFFFFFF0000 and there is no logic for j&6.

This Error has been copied or spread for so many repos.

[crozone]

Agreed, comment should be /* Set x=0xFFFFFFFFFFFFFFFF if x=0xFFFFFFFFFFFF0000, else x=0 */, although maybe something like:

/* Bitwise OR the upper bytes of x over the lower two bytes of x, such that if x was 0xFFFFFFFFFFFF0000, it becomes 0xFFFFFFFFFFFFFFFF. Otherwise, if x was 0, it remains as 0 */