| Index: openssl/crypto/des/asm/readme
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| diff --git a/openssl/crypto/des/asm/readme b/openssl/crypto/des/asm/readme
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| deleted file mode 100644
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| index 1beafe253b17fe52985f7c4de6f7b4577f1f1bfb..0000000000000000000000000000000000000000
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| --- a/openssl/crypto/des/asm/readme
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| +++ /dev/null
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| @@ -1,131 +0,0 @@
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| -First up, let me say I don't like writing in assembler. It is not portable,
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| -dependant on the particular CPU architecture release and is generally a pig
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| -to debug and get right. Having said that, the x86 architecture is probably
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| -the most important for speed due to number of boxes and since
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| -it appears to be the worst architecture to to get
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| -good C compilers for. So due to this, I have lowered myself to do
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| -assembler for the inner DES routines in libdes :-).
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| -
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| -The file to implement in assembler is des_enc.c. Replace the following
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| -4 functions
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| -des_encrypt1(DES_LONG data[2],des_key_schedule ks, int encrypt);
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| -des_encrypt2(DES_LONG data[2],des_key_schedule ks, int encrypt);
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| -des_encrypt3(DES_LONG data[2],des_key_schedule ks1,ks2,ks3);
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| -des_decrypt3(DES_LONG data[2],des_key_schedule ks1,ks2,ks3);
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| -
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| -They encrypt/decrypt the 64 bits held in 'data' using
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| -the 'ks' key schedules. The only difference between the 4 functions is that
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| -des_encrypt2() does not perform IP() or FP() on the data (this is an
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| -optimization for when doing triple DES and des_encrypt3() and des_decrypt3()
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| -perform triple des. The triple DES routines are in here because it does
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| -make a big difference to have them located near the des_encrypt2 function
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| -at link time..
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| -
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| -Now as we all know, there are lots of different operating systems running on
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| -x86 boxes, and unfortunately they normally try to make sure their assembler
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| -formating is not the same as the other peoples.
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| -The 4 main formats I know of are
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| -Microsoft Windows 95/Windows NT
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| -Elf Includes Linux and FreeBSD(?).
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| -a.out The older Linux.
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| -Solaris Same as Elf but different comments :-(.
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| -
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| -Now I was not overly keen to write 4 different copies of the same code,
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| -so I wrote a few perl routines to output the correct assembler, given
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| -a target assembler type. This code is ugly and is just a hack.
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| -The libraries are x86unix.pl and x86ms.pl.
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| -des586.pl, des686.pl and des-som[23].pl are the programs to actually
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| -generate the assembler.
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| -
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| -So to generate elf assembler
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| -perl des-som3.pl elf >dx86-elf.s
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| -For Windows 95/NT
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| -perl des-som2.pl win32 >win32.asm
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| -
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| -[ update 4 Jan 1996 ]
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| -I have added another way to do things.
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| -perl des-som3.pl cpp >dx86-cpp.s
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| -generates a file that will be included by dx86unix.cpp when it is compiled.
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| -To build for elf, a.out, solaris, bsdi etc,
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| -cc -E -DELF asm/dx86unix.cpp | as -o asm/dx86-elf.o
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| -cc -E -DSOL asm/dx86unix.cpp | as -o asm/dx86-sol.o
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| -cc -E -DOUT asm/dx86unix.cpp | as -o asm/dx86-out.o
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| -cc -E -DBSDI asm/dx86unix.cpp | as -o asm/dx86bsdi.o
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| -This was done to cut down the number of files in the distribution.
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| -
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| -Now the ugly part. I acquired my copy of Intels
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| -"Optimization's For Intel's 32-Bit Processors" and found a few interesting
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| -things. First, the aim of the exersize is to 'extract' one byte at a time
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| -from a word and do an array lookup. This involves getting the byte from
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| -the 4 locations in the word and moving it to a new word and doing the lookup.
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| -The most obvious way to do this is
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| -xor eax, eax # clear word
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| -movb al, cl # get low byte
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| -xor edi DWORD PTR 0x100+des_SP[eax] # xor in word
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| -movb al, ch # get next byte
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| -xor edi DWORD PTR 0x300+des_SP[eax] # xor in word
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| -shr ecx 16
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| -which seems ok. For the pentium, this system appears to be the best.
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| -One has to do instruction interleaving to keep both functional units
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| -operating, but it is basically very efficient.
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| -
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| -Now the crunch. When a full register is used after a partial write, eg.
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| -mov al, cl
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| -xor edi, DWORD PTR 0x100+des_SP[eax]
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| -386 - 1 cycle stall
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| -486 - 1 cycle stall
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| -586 - 0 cycle stall
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| -686 - at least 7 cycle stall (page 22 of the above mentioned document).
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| -
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| -So the technique that produces the best results on a pentium, according to
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| -the documentation, will produce hideous results on a pentium pro.
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| -
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| -To get around this, des686.pl will generate code that is not as fast on
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| -a pentium, should be very good on a pentium pro.
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| -mov eax, ecx # copy word
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| -shr ecx, 8 # line up next byte
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| -and eax, 0fch # mask byte
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| -xor edi DWORD PTR 0x100+des_SP[eax] # xor in array lookup
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| -mov eax, ecx # get word
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| -shr ecx 8 # line up next byte
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| -and eax, 0fch # mask byte
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| -xor edi DWORD PTR 0x300+des_SP[eax] # xor in array lookup
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| -
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| -Due to the execution units in the pentium, this actually works quite well.
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| -For a pentium pro it should be very good. This is the type of output
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| -Visual C++ generates.
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| -
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| -There is a third option. instead of using
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| -mov al, ch
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| -which is bad on the pentium pro, one may be able to use
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| -movzx eax, ch
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| -which may not incur the partial write penalty. On the pentium,
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| -this instruction takes 4 cycles so is not worth using but on the
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| -pentium pro it appears it may be worth while. I need access to one to
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| -experiment :-).
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| -
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| -eric (20 Oct 1996)
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| -
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| -22 Nov 1996 - I have asked people to run the 2 different version on pentium
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| -pros and it appears that the intel documentation is wrong. The
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| -mov al,bh is still faster on a pentium pro, so just use the des586.pl
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| -install des686.pl
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| -
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| -3 Dec 1996 - I added des_encrypt3/des_decrypt3 because I have moved these
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| -functions into des_enc.c because it does make a massive performance
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| -difference on some boxes to have the functions code located close to
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| -the des_encrypt2() function.
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| -
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| -9 Jan 1997 - des-som2.pl is now the correct perl script to use for
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| -pentiums. It contains an inner loop from
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| -Svend Olaf Mikkelsen <svolaf@inet.uni-c.dk> which does raw ecb DES calls at
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| -273,000 per second. He had a previous version at 250,000 and the best
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| -I was able to get was 203,000. The content has not changed, this is all
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| -due to instruction sequencing (and actual instructions choice) which is able
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| -to keep both functional units of the pentium going.
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| -We may have lost the ugly register usage restrictions when x86 went 32 bit
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| -but for the pentium it has been replaced by evil instruction ordering tricks.
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| -
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| -13 Jan 1997 - des-som3.pl, more optimizations from Svend Olaf.
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| -raw DES at 281,000 per second on a pentium 100.
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| -
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|