From: Darrick J. Wong <djwong@xxxxxxxxxx>
For some reason, getbitval insists upon collecting a u64 from a pointer
bit by bit if it's not aligned to a 16-byte boundary. If not, then it
resorts to scraping bits individually. I don't know of any platform
where we require 16-byte alignment for a 8-byte access, or why we'd care
now that we have things like get_unaligned_beXX.
Rework this function to detect either naturally aligned accesses and use
the regular beXX_to_cpu functions; or byte-aligned accesses and use the
get_unaligned_beXX functions. Only fall back to the bit scraping
algorithm for the really weird cases.
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
db/bit.c | 37 ++++++++++++++++---------------------
1 file changed, 16 insertions(+), 21 deletions(-)
diff --git a/db/bit.c b/db/bit.c
index c9bfd2eb0..1b9ca054f 100644
--- a/db/bit.c
+++ b/db/bit.c
@@ -55,39 +55,34 @@ getbitval(
char *p;
int64_t rval;
int signext;
- int z1, z2, z3, z4;
ASSERT(nbits<=64);
p = (char *)obj + byteize(bitoff);
bit = bitoffs(bitoff);
signext = (flags & BVSIGNED) != 0;
- z4 = ((intptr_t)p & 0xf) == 0 && bit == 0;
- if (nbits == 64 && z4)
- return be64_to_cpu(*(__be64 *)p);
- z3 = ((intptr_t)p & 0x7) == 0 && bit == 0;
- if (nbits == 32 && z3) {
+
+ if (bit != 0)
+ goto scrape_bits;
+
+ switch (nbits) {
+ case 64:
+ return get_unaligned_be64(p);
+ case 32:
if (signext)
- return (__s32)be32_to_cpu(*(__be32 *)p);
- else
- return (__u32)be32_to_cpu(*(__be32 *)p);
- }
- z2 = ((intptr_t)p & 0x3) == 0 && bit == 0;
- if (nbits == 16 && z2) {
+ return (__s32)get_unaligned_be32(p);
+ return (__u32)get_unaligned_be32(p);
+ case 16:
if (signext)
- return (__s16)be16_to_cpu(*(__be16 *)p);
- else
- return (__u16)be16_to_cpu(*(__be16 *)p);
- }
- z1 = ((intptr_t)p & 0x1) == 0 && bit == 0;
- if (nbits == 8 && z1) {
+ return (__s16)get_unaligned_be16(p);
+ return (__u16)get_unaligned_be16(p);
+ case 8:
if (signext)
return *(__s8 *)p;
- else
- return *(__u8 *)p;
+ return *(__u8 *)p;
}
-
+scrape_bits:
for (i = 0, rval = 0LL; i < nbits; i++) {
if (getbit_l(p, bit + i)) {
/* If the last bit is on and we care about sign
