diff options
Diffstat (limited to 'openssl/crypto/des/asm/readme')
| -rw-r--r-- | openssl/crypto/des/asm/readme | 131 |
1 files changed, 0 insertions, 131 deletions
diff --git a/openssl/crypto/des/asm/readme b/openssl/crypto/des/asm/readme deleted file mode 100644 index 1beafe25..00000000 --- a/openssl/crypto/des/asm/readme +++ /dev/null @@ -1,131 +0,0 @@ -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. - |