Module Name: src
Committed By: dholland
Date: Wed Dec 9 02:46:57 UTC 2020
Modified Files:
src/common/lib/libc/arch/arm/gen: byte_swap_4.S
Log Message:
arm bswap32: Improve the comments showing the byte flow.
It's confusing to use 1-4 for bytes 1-4 and then 0 for literal zero,
so use a-d for bytes 1-4.
To generate a diff of this commit:
cvs rdiff -u -r1.7 -r1.8 src/common/lib/libc/arch/arm/gen/byte_swap_4.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/common/lib/libc/arch/arm/gen/byte_swap_4.S
diff -u src/common/lib/libc/arch/arm/gen/byte_swap_4.S:1.7 src/common/lib/libc/arch/arm/gen/byte_swap_4.S:1.8
--- src/common/lib/libc/arch/arm/gen/byte_swap_4.S:1.7 Mon Aug 19 03:44:47 2013
+++ src/common/lib/libc/arch/arm/gen/byte_swap_4.S Wed Dec 9 02:46:57 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: byte_swap_4.S,v 1.7 2013/08/19 03:44:47 matt Exp $ */
+/* $NetBSD: byte_swap_4.S,v 1.8 2020/12/09 02:46:57 dholland Exp $ */
/*-
* Copyright (c) 1997 The NetBSD Foundation, Inc.
@@ -40,21 +40,21 @@ ENTRY(FUNC)
#ifdef _ARM_ARCH_6
rev r0, r0
#elif !defined(__thumb__)
- eor r1, r0, r0, ror #16 /* 4.3.2.1 -> 42.31.42.31 */
- bic r1, r1, #0x00FF0000 /* 42.31.42.31 -> 42.0.42.31 */
- mov r0, r0, ror #8 /* 4.3.2.1 -> 1.4.3.2 */
- eor r0, r0, r1, lsr #8 /* 1.4.3.2 ^ 0.42.0.42 -> 1.2.3.4 */
+ eor r1, r0, r0, ror #16 /* d.c.b.a -> db.ca.db.ca */
+ bic r1, r1, #0x00FF0000 /* db.ca.db.ca -> db.0.db.ca */
+ mov r0, r0, ror #8 /* d.c.b.a -> a.d.c.b */
+ eor r0, r0, r1, lsr #8 /* a.d.c.b ^ 0.db.0.db -> a.b.c.d */
#else
movs r3, #16
- lsls r1, r0, #8 /* 4.3.2.1 -> 3.2.1.0 /*
- lsrs r0, r0, #8 /* 4.3.2.1 -> 0.4.3.2 */
- rors r1, r3 /* 3.2.1.0 -> 1.0.3.2 */
- rors r0, r3 /* 0.4.3.2 -> 3.2.0.4 */
- lsrs r1, r1, #8 /* 1.0.3.2 -> 0.1.0.3 */
- lsls r1, r1, #8 /* 0.1.0.3 -> 1.0.3.0 */
- lsls r0, r0, #8 /* 3.2.0.4 -> 2.0.4.0 */
- lsrs r0, r0, #8 /* 2.0.4.0 -> 0.2.0.4 */
- orrs r0, r0, r1 /* 1.0.3.0 | 0.2.0.4 -> 1.2.3.4 */
+ lsls r1, r0, #8 /* d.c.b.a -> c.b.a.0 /*
+ lsrs r0, r0, #8 /* d.c.b.a -> 0.d.c.b */
+ rors r1, r3 /* c.b.a.0 -> a.0.c.b */
+ rors r0, r3 /* 0.d.c.b -> c.b.0.d */
+ lsrs r1, r1, #8 /* a.0.c.b -> 0.a.0.c */
+ lsls r1, r1, #8 /* 0.a.0.c -> a.0.c.0 */
+ lsls r0, r0, #8 /* c.b.0.d -> b.0.d.0 */
+ lsrs r0, r0, #8 /* b.0.d.0 -> 0.b.0.d */
+ orrs r0, r0, r1 /* a.0.c.0 | 0.b.0.d -> a.b.c.d */
#endif
RET
END(FUNC)
