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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.
This commit is contained in:
dholland 2020-12-09 02:46:57 +00:00
parent de83a47b93
commit 3818c9a287
1 changed files with 14 additions and 14 deletions
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28
common/lib/libc/arch/arm/gen/byte_swap_4.S
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@ -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)