On Sun, 22 Apr 2007 02:31:26 -0700 Mark Glines <[EMAIL PROTECTED]> wrote:
> On Sat, 21 Apr 2007 18:24:18 -0700 > chromatic <[EMAIL PROTECTED]> wrote: > > Then it calculates a slot value: > > > > const int slot = (reg_alloc + 7) >> 3; > > reg_alloc = slot << 3; > > > > This is where I start not to understand. Why reg_alloc + 7? Why > > shift left and right by 3? > > To me it looks like it's just rounding up to the next 8-byte boundary. Oops, 8-slot boundary. Whatever that means. After that add and shifting stuff, slot is guaranteed to be a multiple of 8. That idiom is pretty common for cache alignment purposes and such, but I usually see it being done to a pointer value, not an integer. Well, perhaps they want the pointer to be cache-aligned. Anyway, "slot" is guaranteed to be a multiple of 8. But that entry might not exist in the array yet, so the next if() statement checks for that, and if not, does a realloc() to ensure there are now slot+1 entries, and zeroes out the new pointers. ...after that point, it gets difficult for me to understand :) Mark
