1 files changed, 29 insertions, 7 deletions

diff --git a/libbb/hash_md5_sha_x86-64.S.sh b/libbb/hash_md5_sha_x86-64.S.sh
index 7e50b64fb..901896e6e 100755
--- a/libbb/hash_md5_sha_x86-64.S.sh
+++ b/libbb/hash_md5_sha_x86-64.S.sh
@@ -6,13 +6,35 @@
 # also contains the diff of the generated file.
 exec >hash_md5_sha_x86-64.S
 
+# There is a way to use XMM registers (which always exist for x86-64!) for W[]
+# For example, if we load W as follows:
+#       %xmm0:  w[0x0] w[0x1] w[0x2] w[0x3]
+#       %xmm4:  w[0x4] w[0x5] w[0x6] w[0x7]
+#       %xmm8:  w[0x8] w[0x9] w[0xa] w[0xb]
+#       %xmm12: w[0xc] w[0xd] w[0xe] w[0xf]
+# then the xor'ing operation to generate next W[0..3] is:
+#       movaps  %xmm0, %xmmT2
+#       palignr $0x8, %xmm4, %xmmT2 # form (w[0x2],w[0x3],w[0x4],w[0x5])
+#       # Right-shifts xmm4:xmmT2 by 8 bytes. Writes shifted result to xmmT2. SSSE3 insn.
+#       movaps  %xmm0, %xmmT13
+#       palignr $0x4,%xmm0,%xmmT13 # form (w[0xd],w[0xe],w[0xf],w[0x0])
+#       xmm0 = xmm0 ^ t2 ^ xmm8 ^ t13
+#       xmm0 = rol32(xmm0,1)    # no such insn, have to use pslld+psrld+or
+# and then results can be extracted for use:
+#       movd    %xmm0, %esi     # new W[0]
+#       pextrd  $1, %xmm0, %esi # new W[1]
+#       # SSE4.1 insn. Can use EXTRACTPS (also SSE4.1)
+#       pextrd  $2, %xmm0, %esi # new W[2]
+#       pextrd  $3, %xmm0, %esi # new W[3]
+# ... but this requires SSE4.1 and SSSE3, which are not universally available on x86-64.
+
 echo \
 '### Generated by hash_md5_sha_x86-64.S.sh ###
 
 #if CONFIG_SHA1_SMALL == 0 && defined(__GNUC__) && defined(__x86_64__)
         .section        .text.sha1_process_block64,"ax",@progbits
-        .globl  sha1_process_block64
-        .hidden sha1_process_block64
+        .globl  sha1_process_block64
+        .hidden sha1_process_block64
         .type   sha1_process_block64, @function
 
         .balign 8       # allow decoders to fetch at least 5 first insns
@@ -265,15 +287,15 @@ RD2 ax bx cx dx bp 75; RD2 bp ax bx cx dx 76; RD2 dx bp ax bx cx 77; RD2 cx dx b
 echo "
         popq    %rdi            #
         popq    %r12            #
-        addl    %eax, 80(%rdi)  # ctx->hash[0] += a
+        addl    %eax, 80(%rdi)  # ctx->hash[0] += a
         popq    %r13            #
-        addl    %ebx, 84(%rdi)  # ctx->hash[1] += b
+        addl    %ebx, 84(%rdi)  # ctx->hash[1] += b
         popq    %r14            #
-        addl    %ecx, 88(%rdi)  # ctx->hash[2] += c
+        addl    %ecx, 88(%rdi)  # ctx->hash[2] += c
         popq    %r15            #
-        addl    %edx, 92(%rdi)  # ctx->hash[3] += d
+        addl    %edx, 92(%rdi)  # ctx->hash[3] += d
         popq    %rbx            #
-        addl    %ebp, 96(%rdi)  # ctx->hash[4] += e
+        addl    %ebp, 96(%rdi)  # ctx->hash[4] += e
         popq    %rbp            #
 
         ret