Back to byte-aligned bitswapping

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@2519 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 58 insertions, 67 deletions

diff --git a/firmware/bitswap.S b/firmware/bitswap.S
index 5f94fed..f825be2 100644
--- a/firmware/bitswap.S
+++ b/firmware/bitswap.S
@@ -17,85 +17,76 @@
  *
  ****************************************************************************/
 
-	.section	.icode,"ax",@progbits
-    	.global		_bitswap
-	.align 		4
-	.type		_bitswap,@function
+    .section    .icode,"ax",@progbits
+    .global     _bitswap
+    .align      4
+    .type       _bitswap,@function
 
 /* Registers used:
  *
- * r0	Temporary (required by some instructions)
- * r1	Low byte
- * r2	High byte
- * r3	Result after flip
- * r4	Data
- * r5	Length
- * r6	Current (position in Data)
- * r7	Flip table
+ * r0   Temporary (required by some instructions)
+ * r1   Flip table
+ * r4   Argument:  Data pointer
+ * r5   Argument:  Length (in bytes)
  */
 
+/* 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,r7
-	mov	r4,r6
-	add	r5,r6				/* goto end of buffer */
-	add	r5,r6				/* (direction IS important) */
-	bra	.init
+    mov.l   .fliptable,r1
+    add r4,r5             /* Calculate end of buffer */
+    bra .init
 .loop:
-	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				/* remove any sign 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				/* remove any sign extend */
-	or	r0,r3				/* put low byte in result */
-	mov.w	r3,@r4				/* store result */
-	add	#2,r4
+    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
 .init:
-	cmp/gt	r4,r6				/* while (data < start+length*2) */
-	bt	.loop
-	rts
+    cmp/gt  r4,r5         /* while (dataptr < start+length) */
+    bt  .loop
+    rts
 
-	.align	4
+    .align  4
 
 .fliptable:
-	.long	_fliptable
+    .long   _fliptable
 
 _fliptable:
-	.byte	0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0
-	.byte	0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0
-	.byte	0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8
-	.byte	0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8
-	.byte	0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4
-	.byte	0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4
-	.byte	0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec
-	.byte	0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc
-	.byte	0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2
-	.byte	0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2
-	.byte	0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea
-	.byte	0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa
-	.byte	0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6
-	.byte	0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6
-	.byte	0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee
-	.byte	0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe
-	.byte	0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1
-	.byte	0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1
-	.byte	0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9
-	.byte	0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9
-	.byte	0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5
-	.byte	0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5
-	.byte	0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed
-	.byte	0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd
-	.byte	0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3
-	.byte	0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3
-	.byte	0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb
-	.byte	0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb
-	.byte	0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7
-	.byte	0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7
-	.byte	0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef
-	.byte	0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
+    .byte   0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0
+    .byte   0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0
+    .byte   0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8
+    .byte   0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8
+    .byte   0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4
+    .byte   0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4
+    .byte   0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec
+    .byte   0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc
+    .byte   0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2
+    .byte   0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2
+    .byte   0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea
+    .byte   0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa
+    .byte   0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6
+    .byte   0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6
+    .byte   0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee
+    .byte   0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe
+    .byte   0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1
+    .byte   0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1
+    .byte   0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9
+    .byte   0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9
+    .byte   0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5
+    .byte   0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5
+    .byte   0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed
+    .byte   0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd
+    .byte   0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3
+    .byte   0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3
+    .byte   0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb
+    .byte   0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb
+    .byte   0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7
+    .byte   0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7
+    .byte   0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef
+    .byte   0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
 
 .end:
-	.size	_bitswap,.end-_bitswap
+    .size   _bitswap,.end-_bitswap