diff options
| author | Linus Nielsen Feltzing <linus@haxx.se> | 2002-10-08 12:14:13 +0000 |
|---|---|---|
| committer | Linus Nielsen Feltzing <linus@haxx.se> | 2002-10-08 12:14:13 +0000 |
| commit | 095c68bc1db6fc73a4ed28e3d6e2e1e963deffd3 (patch) | |
| tree | f97324ff2af9fcdb796aa072487baafe674bef0e | |
| parent | 1e972b53e56cb61ed306ca41896cb28ae2d754ed (diff) | |
| download | rockbox-095c68bc1db6fc73a4ed28e3d6e2e1e963deffd3.zip rockbox-095c68bc1db6fc73a4ed28e3d6e2e1e963deffd3.tar.gz rockbox-095c68bc1db6fc73a4ed28e3d6e2e1e963deffd3.tar.bz2 rockbox-095c68bc1db6fc73a4ed28e3d6e2e1e963deffd3.tar.xz | |
Magnus Holmgrens improved word swap
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@2529 a1c6a512-1295-4272-9138-f99709370657
| -rw-r--r-- | firmware/bitswap.S | 60 |
1 files changed, 44 insertions, 16 deletions
diff --git a/firmware/bitswap.S b/firmware/bitswap.S index f825be2..9a4f760 100644 --- a/firmware/bitswap.S +++ b/firmware/bitswap.S @@ -25,28 +25,56 @@ /* Registers used: * * r0 Temporary (required by some instructions) - * r1 Flip table - * r4 Argument: Data pointer - * r5 Argument: Length (in bytes) + * r1 Low byte + * r2 High byte + * r3 Result after flip + * r4 Data + * r5 Length + * r6 1 + * r7 Flip table */ -/* TODO: Optimize for DRAM burst operation by reading and writing in chunks - We do not want to optimize by reading/writing words, because the data - pointer may be odd */ - _bitswap: - mov.l .fliptable,r1 - add r4,r5 /* Calculate end of buffer */ + mov.l .fliptable,r7 + mov #1,r6 + mov r4,r0 + and #1,r0 /* odd address? */ + cmp/eq #0,r0 + bt .init /* no, address is even */ + + mov.b @r4,r0 /* swap first byte */ + extu.b r0,r0 + mov.b @(r0,r7),r0 + mov.b r0,@r4 + add #1,r4 + add #-1,r5 bra .init .loop: - mov.b @r4,r0 /* Data to flip */ - extu.b r0,r0 /* Zero extend */ - mov.b @(r0,r1),r0 /* Look up in the flip table */ - mov.b r0,@r4 /* Store result */ - add #1,r4 + mov.w @r4,r1 /* data to flip */ + swap.b r1,r2 + extu.b r2,r0 /* high byte */ + mov.b @(r0,r7),r2 + extu.b r2,r0 /* Zero extend */ + swap.b r0,r3 /* put high byte in result */ + extu.b r1,r0 /* low byte */ + mov.b @(r0,r7),r1 + extu.b r1,r0 /* Zero extend */ + or r0,r3 /* put low byte in result */ + mov.w r3,@r4 /* store result */ + add #2,r4 + add #-2,r5 .init: - cmp/gt r4,r5 /* while (dataptr < start+length) */ - bt .loop + cmp/gt r6,r5 /* while [bytes remaining] > 1 */ + bt .loop /* (at least 2 bytes left) */ + + cmp/eq r6,r5 + bf .exit /* if not 1 byte left, exit */ + + mov.b @r4,r0 /* swap last byte */ + extu.b r0,r0 + mov.b @(r0,r7),r0 + mov.b r0,@r4 +.exit: rts .align 4 |