On Tue, Dec 05, 2023 at 12:33:05PM +0800, John Sanpe wrote:
> Replace the internal table lookup algorithm with the hweight
> library, which has instruction set acceleration capabilities.
>
> Use it to increase the length of a single calculation of
> the exfat_find_free_bitmap function to the long type.
Have you run sparse over this? "make C=2" will do it for you if you
have sparse installed. I think it's going to complain about missing
endianness annotations.
> + for (i = 0; i < total_clus; i += BITS_PER_LONG) {
> + bitmap = (void *)(sbi->vol_amap[map_i]->b_data + map_b);
> + clu_bits = lel_to_cpu(*bitmap);
I understand why you need to byteswap at the end, but I don't understand
why you need to byteswap here. You're asking how many bits are set,
and that's the same answer no matter whether you calculate it on
0x12345678 or on 0x78563412.
> +++ b/fs/exfat/exfat_fs.h
> @@ -136,6 +136,7 @@ enum {
> #define BITMAP_OFFSET_BYTE_IN_SECTOR(sb, ent) \
> ((ent / BITS_PER_BYTE) & ((sb)->s_blocksize - 1))
> #define BITS_PER_BYTE_MASK 0x7
> +#define BITS_PER_LONG_MASK (BITS_PER_LONG - 1)
I don't think this adds any value over just using (BITS_PER_LONG - 1)
directly.
