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Diffstat (limited to 'sysdeps/powerpc/strlen.s')
| -rw-r--r-- | sysdeps/powerpc/strlen.s | 144 |
1 files changed, 0 insertions, 144 deletions
diff --git a/sysdeps/powerpc/strlen.s b/sysdeps/powerpc/strlen.s deleted file mode 100644 index ea809772eb..0000000000 --- a/sysdeps/powerpc/strlen.s +++ /dev/null @@ -1,144 +0,0 @@ - # Optimized strlen implementation for PowerPC. - # Copyright (C) 1997 Free Software Foundation, Inc. - # This file is part of the GNU C Library. - # - # The GNU C Library is free software; you can redistribute it and/or - # modify it under the terms of the GNU Library General Public License as - # published by the Free Software Foundation; either version 2 of the - # License, or (at your option) any later version. - # - # The GNU C Library is distributed in the hope that it will be useful, - # but WITHOUT ANY WARRANTY; without even the implied warranty of - # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - # Library General Public License for more details. - # - # You should have received a copy of the GNU Library General Public - # License along with the GNU C Library; see the file COPYING.LIB. If not, - # write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, - # Boston, MA 02111-1307, USA. - - # The algorithm here uses the following techniques: - # - # 1) Given a word 'x', we can test to see if it contains any 0 bytes - # by subtracting 0x01010101, and seeing if any of the high bits of each - # byte changed from 0 to 1. This works because the least significant - # 0 byte must have had no incoming carry (otherwise it's not the least - # significant), so it is 0x00 - 0x01 == 0xff. For all other - # byte values, either they have the high bit set initially, or when - # 1 is subtracted you get a value in the range 0x00-0x7f, none of which - # have their high bit set. The expression here is - # (x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when - # there were no 0x00 bytes in the word. - # - # 2) Given a word 'x', we can test to see _which_ byte was zero by - # calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f). - # This produces 0x80 in each byte that was zero, and 0x00 in all - # the other bytes. The '| 0x7f7f7f7f' clears the low 7 bits in each - # byte, and the '| x' part ensures that bytes with the high bit set - # produce 0x00. The addition will carry into the high bit of each byte - # iff that byte had one of its low 7 bits set. We can then just see - # which was the most significant bit set and divide by 8 to find how - # many to add to the index. - # This is from the book 'The PowerPC Compiler Writer's Guide', - # by Steve Hoxey, Faraydon Karim, Bill Hay and Hank Warren. - # - # We deal with strings not aligned to a word boundary by taking the - # first word and ensuring that bytes not part of the string - # are treated as nonzero. To allow for memory latency, we unroll the - # loop a few times, being careful to ensure that we do not read ahead - # across cache line boundaries. - # - # Questions to answer: - # 1) How long are strings passed to strlen? If they're often really long, - # we should probably use cache management instructions and/or unroll the - # loop more. If they're often quite short, it might be better to use - # fact (2) in the inner loop than have to recalculate it. - # 2) How popular are bytes with the high bit set? If they are very rare, - # on some processors it might be useful to use the simpler expression - # ~((x - 0x01010101) | 0x7f7f7f7f) (that is, on processors with only one - # ALU), but this fails when any character has its high bit set. - - # Some notes on register usage: Under the SVR4 ABI, we can use registers - # 0 and 3 through 12 (so long as we don't call any procedures) without - # saving them. We can also use registers 14 through 31 if we save them. - # We can't use r1 (it's the stack pointer), r2 nor r13 because the user - # program may expect them to hold their usual value if we get sent - # a signal. Integer parameters are passed in r3 through r10. - # We can use condition registers cr0, cr1, cr5, cr6, and cr7 without saving - # them, the others we must save. - - .section ".text" - .align 2 - .globl strlen - .type strlen,@function -strlen: - # On entry, r3 points to the string, and it's left that way. - # We use r6 to store 0xfefefeff, and r7 to store 0x7f7f7f7f. - # r4 is used to keep the current index into the string; r5 holds - # the number of padding bits we prepend to the string to make it - # start at a word boundary. r8 holds the 'current' word. - # r9-12 are temporaries. r0 is used as a temporary and for discarded - # results. - clrrwi %r4,%r3,2 - lis %r7,0x7f7f - rlwinm %r5,%r3,3,27,28 - lwz %r8,0(%r4) - li %r9,-1 - addi %r7,%r7,0x7f7f - # That's the setup done, now do the first pair of words. - # We make an exception and use method (2) on the first two words, to reduce - # overhead. - srw %r9,%r9,%r5 - and %r0,%r7,%r8 - or %r10,%r7,%r8 - add %r0,%r0,%r7 - nor %r0,%r10,%r0 - and. %r8,%r0,%r9 - mtcrf 0x01,%r3 - bne done0 - lis %r6,0xfeff - addi %r6,%r6,-0x101 - # Are we now aligned to a doubleword boundary? - bt 29,loop - - # Handle second word of pair. - lwzu %r8,4(%r4) - and %r0,%r7,%r8 - or %r10,%r7,%r8 - add %r0,%r0,%r7 - nor. %r8,%r10,%r0 - bne done0 - - # The loop. - -loop: lwz %r8,4(%r4) - lwzu %r9,8(%r4) - add %r0,%r6,%r8 - nor %r10,%r7,%r8 - and. %r0,%r0,%r10 - add %r11,%r6,%r9 - nor %r12,%r7,%r9 - bne done1 - and. %r0,%r11,%r12 - beq loop - - and %r0,%r7,%r9 - add %r0,%r0,%r7 - andc %r8,%r12,%r0 - b done0 - -done1: and %r0,%r7,%r8 - subi %r4,%r4,4 - add %r0,%r0,%r7 - andc %r8,%r10,%r0 - - # When we get to here, r4 points to the first word in the string that - # contains a zero byte, and the most significant set bit in r8 is in that - # byte. -done0: cntlzw %r11,%r8 - subf %r0,%r3,%r4 - srwi %r11,%r11,3 - add %r3,%r0,%r11 - blr -0: - .size strlen,0b-strlen |