forked from len0rd/rockbox
patch #919088: 17% faster bitswap(), by Jens "SH" Arnold
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4407 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Jörg Hohensohn
parent
b61cf76aba
commit
e64256d499
1 changed files with 89 additions and 71 deletions
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@ -7,7 +7,7 @@
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* \/ \/ \/ \/ \/
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* \/ \/ \/ \/ \/
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* $Id$
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* $Id$
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*
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*
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* Copyright (C) 2002 by Magnus Holmgren
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* Copyright (C) 2004 by Jens Arnold
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*
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*
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* All files in this archive are subject to the GNU General Public License.
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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* See the file COPYING in the source tree root for full license agreement.
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@ -22,67 +22,87 @@
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.global _bitswap
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.global _bitswap
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.type _bitswap,@function
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.type _bitswap,@function
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/* Registers used:
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/* Flips the bits of all bytes in a memory area (required for mp3 data on
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* the Archos). This version is optimized for speed and size.
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*
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*
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* r0 Temporary (required by some instructions)
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* arguments:
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* r1 Low byte
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* r4 - start address
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* r2 High byte / final result
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* r5 - length
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* r4 &Data
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*
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* r5 Length
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* return value: void
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* r7 Flip table
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*
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*/
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* register usage:
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* r0 - temporary
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/* The instruction order below is a bit strange, because:
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* r1 - bit mask for rounding to long bound / low byte (after swap)
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* 1) Keeping load/stores on longword boundaries means the instruction fetch
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* r2 - high byte (after swap) / combined result
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* won't compete with the memory access (because instructions are fetched
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* r4 - data address - 4
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* in pairs).
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* r5 - end address - 4
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* 2) Using the result of a fetch in the next instruction causes a stall
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* r7 - flip table (addressing with signed offset)
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* (except in certain circumstances).
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*
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* See the SH-1 programming manual for details.
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* The instruction order below is devised in a way to utilize the pipelining
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* of the SH1 to the max.
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*/
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*/
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_bitswap:
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_bitswap:
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mov.l .fliptable,r7
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mova _fliptable,r0
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add #-2,r4 /* ptr is used shifted by 2 */
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mov r0,r7
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add r4,r5 /* r5 = end_address - 2 */
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add #-4,r4 /* address is shifted by 4 */
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add #-1,r5 /* r5 = &last_byte - 2 */
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add r4,r5 /* r5 = end_address - 4 */
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cmp/hi r4,r5 /* at least something to do? */
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bf .exit /* no, get out of here! */
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add #-3,r5 /* end offset for flipping 4 bytes per pass */
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mov r4,r0
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mov r4,r0
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tst #1,r0 /* even address? */
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tst #1,r0 /* even address? */
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bt .init /* yes */
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bt .start2_w /* yes, jump into main loop */
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add #1,r4 /* r4 now even */
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/* no, flip first byte */
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mov.b @(1,r4),r0 /* no, swap first byte */
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mov.b @(4,r4),r0 /* load byte, sign extension! */
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extu.b r0,r0
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add #1,r4 /* early increment */
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mov.b @(r0,r7),r0
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mov.b @(r0,r7),r0 /* fliptable offset is signed */
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mov.b r0,@(1,r4)
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bra .start2_w /* jump into main loop */
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mov.b r0,@(3,r4) /* store byte */
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.init:
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/* main loop: flips 2 words per pass */
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cmp/hi r4,r5 /* at least 2 bytes to swap? */
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.align 2
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bf .last /* no, skip main loop */
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.loop2_w:
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mov.w @(6,r4),r0 /* load second word */
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add #4,r4 /* early increment */
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swap.b r0,r2 /* get high byte (2nd word) */
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exts.b r0,r0 /* prepare low byte (2nd word) */
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mov.b @(r0,r7),r1 /* swap low byte (2nd word) */
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exts.b r2,r0 /* prepare high byte (2nd word) */
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mov.b @(r0,r7),r2 /* swap high byte (2nd word) */
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extu.b r1,r0 /* zero extend low byte (2nd word) */
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mov.w @r4,r1 /* load first word */
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shll8 r2 /* shift high byte (2nd word), low byte zeroed */
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or r2,r0 /* put low byte (2nd word) in result */
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swap.b r1,r2 /* get high byte (1st word) */
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mov.w r0,@(2,r4) /* store result (2nd word) */
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exts.b r1,r0 /* prepare low byte (1st word) */
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mov.b @(r0,r7),r1 /* swap low byte (1st word) */
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exts.b r2,r0 /* prepare high byte (1st word) */
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mov.b @(r0,r7),r2 /* swap high byte (1st word) */
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extu.b r1,r0 /* zero extend low byte (1st word) */
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shll8 r2 /* shift high byte (1st word), low byte zeroed */
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or r2,r0 /* put low byte (1st word) in result */
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mov.w r0,@r4 /* store result (1st word) */
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.start2_w:
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cmp/hi r4,r5 /* runs r4 up to last long bound */
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bt .loop2_w
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.loop:
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bra .start_b2 /* jump into trailing byte loop */
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mov.w @(2,r4),r0 /* data to flip */
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add #3,r5 /* reset end offset */
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add #2,r4 /* early increment */
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swap.b r0,r2 /* get high byte */
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extu.b r0,r0 /* prepare low byte */
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mov.b @(r0,r7),r1 /* swap low byte */
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extu.b r2,r0 /* prepare high byte */
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mov.b @(r0,r7),r2 /* swap high byte */
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extu.b r1,r1 /* zero extend low byte */
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shll8 r2 /* shift high byte, low byte zeroed */
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or r1,r2 /* put low byte in result */
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mov.w r2,@r4 /* store result, ptr already incr'd */
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cmp/hi r4,r5 /* while &last_byte > data */
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bt .loop
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.last:
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/* trailing byte loop: flips 0..3 bytes */
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cmp/eq r4,r5 /* if behind (&last_byte - 2), exit */
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.loop_b2:
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bf .exit
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mov.b @(4,r4),r0 /* loand byte, sign extension! */
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add #1,r4 /* early increment */
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mov.b @(2,r4),r0 /* swap last byte */
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mov.b @(r0,r7),r0 /* fliptable offset is signed */
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extu.b r0,r0
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mov.b r0,@(3,r4) /* store byte */
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mov.b @(r0,r7),r0
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.start_b2:
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mov.b r0,@(2,r4)
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cmp/hi r4,r5 /* runs r4 up to end address */
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bt .loop_b2
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.exit:
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.exit:
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rts
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rts
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@ -90,9 +110,22 @@ _bitswap:
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.align 2
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.align 2
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.fliptable:
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.byte 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1
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.long _fliptable
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.byte 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1
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.byte 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9
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.byte 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9
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.byte 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5
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.byte 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5
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.byte 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed
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.byte 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd
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.byte 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3
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.byte 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3
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.byte 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb
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.byte 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb
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.byte 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7
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.byte 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7
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.byte 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef
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.byte 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
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_fliptable:
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_fliptable:
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.byte 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0
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.byte 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0
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.byte 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0
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.byte 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0
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@ -110,22 +143,7 @@ _fliptable:
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.byte 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6
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.byte 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6
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.byte 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee
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.byte 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee
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.byte 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe
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.byte 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe
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.byte 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1
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.byte 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1
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.byte 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9
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.byte 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9
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.byte 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5
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.byte 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5
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.byte 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed
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.byte 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd
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.byte 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3
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.byte 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3
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.byte 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb
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.byte 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb
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.byte 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7
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.byte 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7
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.byte 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef
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.byte 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
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.end:
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.end:
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.size _bitswap,.end-_bitswap
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.size _bitswap,.end-_bitswap
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