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author | Denys Vlasenko <vda.linux@googlemail.com> | 2022-01-08 22:43:24 +0100 |
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committer | Denys Vlasenko <vda.linux@googlemail.com> | 2022-01-08 22:43:24 +0100 |
commit | 143356876b5712c28b8af61ea9144959a4dc6a5b (patch) | |
tree | e031e951e2b4a4a4bf859a16786dabd2c6281989 | |
parent | e2952dfaff67f3641d3a6d3226753356170ff808 (diff) | |
download | busybox-w32-143356876b5712c28b8af61ea9144959a4dc6a5b.tar.gz busybox-w32-143356876b5712c28b8af61ea9144959a4dc6a5b.tar.bz2 busybox-w32-143356876b5712c28b8af61ea9144959a4dc6a5b.zip |
libbb/sha1: add a comment
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rwxr-xr-x | libbb/hash_md5_sha_x86-64.S.sh | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/libbb/hash_md5_sha_x86-64.S.sh b/libbb/hash_md5_sha_x86-64.S.sh index eef009590..901896e6e 100755 --- a/libbb/hash_md5_sha_x86-64.S.sh +++ b/libbb/hash_md5_sha_x86-64.S.sh | |||
@@ -6,6 +6,28 @@ | |||
6 | # also contains the diff of the generated file. | 6 | # also contains the diff of the generated file. |
7 | exec >hash_md5_sha_x86-64.S | 7 | exec >hash_md5_sha_x86-64.S |
8 | 8 | ||
9 | # There is a way to use XMM registers (which always exist for x86-64!) for W[] | ||
10 | # For example, if we load W as follows: | ||
11 | # %xmm0: w[0x0] w[0x1] w[0x2] w[0x3] | ||
12 | # %xmm4: w[0x4] w[0x5] w[0x6] w[0x7] | ||
13 | # %xmm8: w[0x8] w[0x9] w[0xa] w[0xb] | ||
14 | # %xmm12: w[0xc] w[0xd] w[0xe] w[0xf] | ||
15 | # then the xor'ing operation to generate next W[0..3] is: | ||
16 | # movaps %xmm0, %xmmT2 | ||
17 | # palignr $0x8, %xmm4, %xmmT2 # form (w[0x2],w[0x3],w[0x4],w[0x5]) | ||
18 | # # Right-shifts xmm4:xmmT2 by 8 bytes. Writes shifted result to xmmT2. SSSE3 insn. | ||
19 | # movaps %xmm0, %xmmT13 | ||
20 | # palignr $0x4,%xmm0,%xmmT13 # form (w[0xd],w[0xe],w[0xf],w[0x0]) | ||
21 | # xmm0 = xmm0 ^ t2 ^ xmm8 ^ t13 | ||
22 | # xmm0 = rol32(xmm0,1) # no such insn, have to use pslld+psrld+or | ||
23 | # and then results can be extracted for use: | ||
24 | # movd %xmm0, %esi # new W[0] | ||
25 | # pextrd $1, %xmm0, %esi # new W[1] | ||
26 | # # SSE4.1 insn. Can use EXTRACTPS (also SSE4.1) | ||
27 | # pextrd $2, %xmm0, %esi # new W[2] | ||
28 | # pextrd $3, %xmm0, %esi # new W[3] | ||
29 | # ... but this requires SSE4.1 and SSSE3, which are not universally available on x86-64. | ||
30 | |||
9 | echo \ | 31 | echo \ |
10 | '### Generated by hash_md5_sha_x86-64.S.sh ### | 32 | '### Generated by hash_md5_sha_x86-64.S.sh ### |
11 | 33 | ||