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Diffstat (limited to 'sys/arch/mvme68k/stand/sboot/oc_cksum.S')
| -rw-r--r-- | sys/arch/mvme68k/stand/sboot/oc_cksum.S | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/sys/arch/mvme68k/stand/sboot/oc_cksum.S b/sys/arch/mvme68k/stand/sboot/oc_cksum.S new file mode 100644 index 00000000000..2c9d6a63a24 --- /dev/null +++ b/sys/arch/mvme68k/stand/sboot/oc_cksum.S @@ -0,0 +1,187 @@ +| $NetBSD: oc_cksum.s,v 1.4 1994/10/26 07:51:13 cgd Exp $ + +| Copyright (c) 1988 Regents of the University of California. +| All rights reserved. +| +| Redistribution and use in source and binary forms, with or without +| modification, are permitted provided that the following conditions +| are met: +| 1. Redistributions of source code must retain the above copyright +| notice, this list of conditions and the following disclaimer. +| 2. Redistributions in binary form must reproduce the above copyright +| notice, this list of conditions and the following disclaimer in the +| documentation and/or other materials provided with the distribution. +| 3. All advertising materials mentioning features or use of this software +| must display the following acknowledgement: +| This product includes software developed by the University of +| California, Berkeley and its contributors. +| 4. Neither the name of the University nor the names of its contributors +| may be used to endorse or promote products derived from this software +| without specific prior written permission. +| +| THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +| ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +| IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +| ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +| FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +| DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +| OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +| HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +| LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +| OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +| SUCH DAMAGE. +| +| @(#)oc_cksum.s 7.2 (Berkeley) 11/3/90 +| +| +| oc_cksum: ones complement 16 bit checksum for MC68020. +| +| oc_cksum (buffer, count, strtval) +| +| Do a 16 bit ones complement sum of 'count' bytes from 'buffer'. +| 'strtval' is the starting value of the sum (usually zero). +| +| It simplifies life in in_cksum if strtval can be >= 2^16. +| This routine will work as long as strtval is < 2^31. +| +| Performance +| ----------- +| This routine is intended for MC 68020s but should also work +| for 68030s. It (deliberately) does not worry about the alignment +| of the buffer so will only work on a 68010 if the buffer is +| aligned on an even address. (Also, a routine written to use +| 68010 "loop mode" would almost certainly be faster than this +| code on a 68010). +| +| We do not worry about alignment because this routine is frequently +| called with small counts: 20 bytes for IP header checksums and 40 +| bytes for TCP ack checksums. For these small counts, testing for +| bad alignment adds ~10% to the per-call cost. Since, by the nature +| of the kernel allocator, the data we are called with is almost +| always longword aligned, there is no benefit to this added cost +| and we are better off letting the loop take a big performance hit +| in the rare cases where we are handed an unaligned buffer. +| +| Loop unrolling constants of 2, 4, 8, 16, 32 and 64 times were +| tested on random data on four different types of processors (see +| list below -- 64 was the largest unrolling because anything more +| overflows the 68020 Icache). On all the processors, the +| throughput asymptote was located between 8 and 16 (closer to 8). +| However, 16 was substantially better than 8 for small counts. +| (It is clear why this happens for a count of 40: unroll-8 pays a +| loop branch cost and unroll-16 does not. But the tests also showed +| that 16 was better than 8 for a count of 20. It is not obvious to +| me why.) So, since 16 was good for both large and small counts, +| the loop below is unrolled 16 times. +| +| The processors tested and their average time to checksum 1024 bytes +| of random data were: +| Sun 3/50 (15MHz) 190 us/KB +| Sun 3/180 (16.6MHz) 175 us/KB +| Sun 3/60 (20MHz) 134 us/KB +| Sun 3/280 (25MHz) 95 us/KB +| +| The cost of calling this routine was typically 10% of the per- +| kilobyte cost. E.g., checksumming zero bytes on a 3/60 cost 9us +| and each additional byte cost 125ns. With the high fixed cost, +| it would clearly be a gain to "inline" this routine -- the +| subroutine call adds 400% overhead to an IP header checksum. +| However, in absolute terms, inlining would only gain 10us per +| packet -- a 1% effect for a 1ms ethernet packet. This is not +| enough gain to be worth the effort. + +#include <machine/asm.h> + + .text + + .text; .even; .globl _oc_cksum; _oc_cksum: + movl sp@(4),a0 | get buffer ptr + movl sp@(8),d1 | get byte count + movl sp@(12),d0 | get starting value + movl d2,sp@- | free a reg + + | test for possible 1, 2 or 3 bytes of excess at end + | of buffer. The usual case is no excess (the usual + | case is header checksums) so we give that the faster + | 'not taken' leg of the compare. (We do the excess + | first because we are about the trash the low order + | bits of the count in d1.) + + btst #0,d1 + jne L5 | if one or three bytes excess + btst #1,d1 + jne L7 | if two bytes excess +L1: + movl d1,d2 + lsrl #6,d1 | make cnt into # of 64 byte chunks + andl #0x3c,d2 | then find fractions of a chunk + negl d2 + andb #0xf,cc | clear X + jmp pc@(L3-.-2:b,d2) +L2: + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 + movl a0@+,d2 + addxl d2,d0 +L3: + dbra d1,L2 | (NB- dbra does not affect X) + + movl d0,d1 | fold 32 bit sum to 16 bits + swap d1 | (NB- swap does not affect X) + addxw d1,d0 + jcc L4 + addw #1,d0 +L4: + andl #0xffff,d0 + movl sp@+,d2 + rts + +L5: | deal with 1 or 3 excess bytes at the end of the buffer. + btst #1,d1 + jeq L6 | if 1 excess + + | 3 bytes excess + clrl d2 + movw a0@(-3,d1:l),d2 | add in last full word then drop + addl d2,d0 | through to pick up last byte + +L6: | 1 byte excess + clrl d2 + movb a0@(-1,d1:l),d2 + lsll #8,d2 + addl d2,d0 + jra L1 + +L7: | 2 bytes excess + clrl d2 + movw a0@(-2,d1:l),d2 + addl d2,d0 + jra L1 |