+++ /dev/null
-First up, let me say I don't like writing in assembler. It is not portable,
-dependant on the particular CPU architecture release and is generally a pig
-to debug and get right. Having said that, the x86 architecture is probably
-the most important for speed due to number of boxes and since
-it appears to be the worst architecture to to get
-good C compilers for. So due to this, I have lowered myself to do
-assembler for the inner DES routines in libdes :-).
-
-The file to implement in assembler is des_enc.c. Replace the following
-4 functions
-des_encrypt1(DES_LONG data[2],des_key_schedule ks, int encrypt);
-des_encrypt2(DES_LONG data[2],des_key_schedule ks, int encrypt);
-des_encrypt3(DES_LONG data[2],des_key_schedule ks1,ks2,ks3);
-des_decrypt3(DES_LONG data[2],des_key_schedule ks1,ks2,ks3);
-
-They encrypt/decrypt the 64 bits held in 'data' using
-the 'ks' key schedules. The only difference between the 4 functions is that
-des_encrypt2() does not perform IP() or FP() on the data (this is an
-optimization for when doing triple DES and des_encrypt3() and des_decrypt3()
-perform triple des. The triple DES routines are in here because it does
-make a big difference to have them located near the des_encrypt2 function
-at link time..
-
-Now as we all know, there are lots of different operating systems running on
-x86 boxes, and unfortunately they normally try to make sure their assembler
-formating is not the same as the other peoples.
-The 4 main formats I know of are
-Microsoft Windows 95/Windows NT
-Elf Includes Linux and FreeBSD(?).
-a.out The older Linux.
-Solaris Same as Elf but different comments :-(.
-
-Now I was not overly keen to write 4 different copies of the same code,
-so I wrote a few perl routines to output the correct assembler, given
-a target assembler type. This code is ugly and is just a hack.
-The libraries are x86unix.pl and x86ms.pl.
-des586.pl, des686.pl and des-som[23].pl are the programs to actually
-generate the assembler.
-
-So to generate elf assembler
-perl des-som3.pl elf >dx86-elf.s
-For Windows 95/NT
-perl des-som2.pl win32 >win32.asm
-
-[ update 4 Jan 1996 ]
-I have added another way to do things.
-perl des-som3.pl cpp >dx86-cpp.s
-generates a file that will be included by dx86unix.cpp when it is compiled.
-To build for elf, a.out, solaris, bsdi etc,
-cc -E -DELF asm/dx86unix.cpp | as -o asm/dx86-elf.o
-cc -E -DSOL asm/dx86unix.cpp | as -o asm/dx86-sol.o
-cc -E -DOUT asm/dx86unix.cpp | as -o asm/dx86-out.o
-cc -E -DBSDI asm/dx86unix.cpp | as -o asm/dx86bsdi.o
-This was done to cut down the number of files in the distribution.
-
-Now the ugly part. I acquired my copy of Intels
-"Optimization's For Intel's 32-Bit Processors" and found a few interesting
-things. First, the aim of the exersize is to 'extract' one byte at a time
-from a word and do an array lookup. This involves getting the byte from
-the 4 locations in the word and moving it to a new word and doing the lookup.
-The most obvious way to do this is
-xor eax, eax # clear word
-movb al, cl # get low byte
-xor edi DWORD PTR 0x100+des_SP[eax] # xor in word
-movb al, ch # get next byte
-xor edi DWORD PTR 0x300+des_SP[eax] # xor in word
-shr ecx 16
-which seems ok. For the pentium, this system appears to be the best.
-One has to do instruction interleaving to keep both functional units
-operating, but it is basically very efficient.
-
-Now the crunch. When a full register is used after a partial write, eg.
-mov al, cl
-xor edi, DWORD PTR 0x100+des_SP[eax]
-386 - 1 cycle stall
-486 - 1 cycle stall
-586 - 0 cycle stall
-686 - at least 7 cycle stall (page 22 of the above mentioned document).
-
-So the technique that produces the best results on a pentium, according to
-the documentation, will produce hideous results on a pentium pro.
-
-To get around this, des686.pl will generate code that is not as fast on
-a pentium, should be very good on a pentium pro.
-mov eax, ecx # copy word
-shr ecx, 8 # line up next byte
-and eax, 0fch # mask byte
-xor edi DWORD PTR 0x100+des_SP[eax] # xor in array lookup
-mov eax, ecx # get word
-shr ecx 8 # line up next byte
-and eax, 0fch # mask byte
-xor edi DWORD PTR 0x300+des_SP[eax] # xor in array lookup
-
-Due to the execution units in the pentium, this actually works quite well.
-For a pentium pro it should be very good. This is the type of output
-Visual C++ generates.
-
-There is a third option. instead of using
-mov al, ch
-which is bad on the pentium pro, one may be able to use
-movzx eax, ch
-which may not incur the partial write penalty. On the pentium,
-this instruction takes 4 cycles so is not worth using but on the
-pentium pro it appears it may be worth while. I need access to one to
-experiment :-).
-
-eric (20 Oct 1996)
-
-22 Nov 1996 - I have asked people to run the 2 different version on pentium
-pros and it appears that the intel documentation is wrong. The
-mov al,bh is still faster on a pentium pro, so just use the des586.pl
-install des686.pl
-
-3 Dec 1996 - I added des_encrypt3/des_decrypt3 because I have moved these
-functions into des_enc.c because it does make a massive performance
-difference on some boxes to have the functions code located close to
-the des_encrypt2() function.
-
-9 Jan 1997 - des-som2.pl is now the correct perl script to use for
-pentiums. It contains an inner loop from
-Svend Olaf Mikkelsen <svolaf@inet.uni-c.dk> which does raw ecb DES calls at
-273,000 per second. He had a previous version at 250,000 and the best
-I was able to get was 203,000. The content has not changed, this is all
-due to instruction sequencing (and actual instructions choice) which is able
-to keep both functional units of the pentium going.
-We may have lost the ugly register usage restrictions when x86 went 32 bit
-but for the pentium it has been replaced by evil instruction ordering tricks.
-
-13 Jan 1997 - des-som3.pl, more optimizations from Svend Olaf.
-raw DES at 281,000 per second on a pentium 100.
-
projects / bcm963xx.git / blobdiff