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patch #910193 by Jens Arnold: smaller and faster descramble/RoLo

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4365 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Jörg Hohensohn 2004-03-11 17:07:08 +00:00
parent 53ada3ab88
commit 75c25388d9
1 changed files with 54 additions and 63 deletions
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117
firmware/descramble.S
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@ -7,7 +7,7 @@
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2003 by Magnus Holmgren
* Copyright (C) 2004 by Jens Arnold
*
* All files in this archive are subject to the GNU General Public License.
* See the file COPYING in the source tree root for full license agreement.
@ -34,67 +34,59 @@
* r4 - source (unsigned char*)
* r5 - dest (unsigned char*)
* r6 - len (unsigned int)
*/
/* Register usage:
* i - r0
* i4 - r1
* checksum - r2
* addr - r3
* source - r4
* dest - r5
* len - r6
* len4 - r7
* data - r8
* temp - r9
*
* Register usage:
* r0 - data
* r1 - temp
* r2 - checksum
* r3 - current src address
* r4 - source
* r5 - dest
* r6 - len -> source_end
* r7 - dest_end
* r8 - len / 4
*/
_descramble:
mov.l r8,@-r15
mov.l r9,@-r15
mov #0,r0 /* i = 0 */
mov #0,r1 /* i4 = i / 4 */
mov #0,r2 /* checksum = 0 */
mov r6,r8
shlr2 r8 /* r8 = len / 4 */
mov r5,r7
add r6,r7 /* dest_end = dest + len */
add r4,r6 /* source_end = source + len */
mov r4,r3 /* addr = source */
mov r6,r7
shlr2 r7 /* len4 = len / 4 */
mov #0,r2 /* checksum = 0 */
.loop:
mov.b @r3,r8 /* data = source[addr] */
add r7,r3 /* addr += len4 */
extu.b r8,r8 /* we want the data extended unsigned */
shlr r8 /* start rotate right of low byte */
movt r9 /* get bit 0 that was shifted out */
shll8 r9
shlr r9 /* move it to bit 7 */
or r9,r8 /* finish rotate right */
not r8,r8
extu.b r8,r8
mov.b r8,@(r0,r5) /* dest[i] = data */
add r8,r2 /* checksum += data[i] */
add #1,r0 /* i++ */
tst #3,r0 /* reset addr? */
bf .loop
mov.b @r3,r0 /* data = *addr */
add r8,r3 /* addr += len / 4 */
extu.b r0,r0 /* zero extend data byte */
swap.b r0,r1 /* byte swap low word to temp */
or r1,r0 /* r0's two lower bytes now identical */
shlr r0 /* -> this equals "rotr.b r0" now */
not r0,r0 /* negate */
extu.b r0,r0 /* zero extend low byte (only needed for sum) */
mov.b r0,@r5 /* *dest = data */
add r0,r2 /* checksum += data */
add #1,r5 /* dest++ */
cmp/hi r3,r6 /* addr < source_end ? */
bt .loop
add #1,r1 /* i4++ */
mov r4,r3
add r1,r3 /* addr = source + i4 */
cmp/hs r6,r0 /* all done? */
bf .loop
/* 17 cycles if no "reset," 22 if reset => average 18.25 cycles per
* byte, assuming no wait states from reads or writes. "Old" algorithm
* needed 24-26 cycles per byte, under the same assumptions.
*/
add #1,r4 /* source++ */
mov r4,r3 /* addr = source */
cmp/hi r5,r7 /* dest < dest_end */
bt .loop
/* 15 clock cycles if no reset of source address, 19 if reset,
* avg. 16 cycles per byte. Magnus' Version needed 17-22 cycles per byte
*/
mov.l @r15+,r9
mov.l @r15+,r8
rts
extu.w r2,r0
/* Move len bytes from source to dest (which must be suitably aligned for
/* Move len bytes from source to dest (which must be suitably aligned for
* long moves) and jump to dest + 0x200.
*
* Arguments:
@ -103,26 +95,25 @@ _descramble:
* r6 - len
*/
.align 2
.global _rolo_restart
.type _rolo_restart,@function
_rolo_restart:
mov.w .offset,r0
mov r5,r7
add r0,r7 /* start_func() */
mov r6,r0
shlr2 r0
add #1,r0
.copy:
mov.l @r4+,r1
add #-1,r0
mov.l r1,@r5
add #4,r5
cmp/eq #0,r0
bf .copy
mov r5,r0
sub r4,r0 /* r0 = dest - source */
add #-4,r0 /* adjust for early increment */
add r4,r6 /* r6 = source + len */
mov.w .offset,r1
add r1,r5 /* start_func() */
jmp @r7
.copy: /* loop takes 6 cycles per longword */
mov.l @r4+,r1
cmp/hi r4,r6
mov.l r1,@(r0,r4)
bt .copy
jmp @r5
nop
.offset: