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Diffstat (limited to 'sysdeps/powerpc/powerpc32/strlen.S')
| -rw-r--r-- | sysdeps/powerpc/powerpc32/strlen.S | 190 |
1 files changed, 0 insertions, 190 deletions
diff --git a/sysdeps/powerpc/powerpc32/strlen.S b/sysdeps/powerpc/powerpc32/strlen.S deleted file mode 100644 index fa245f0760..0000000000 --- a/sysdeps/powerpc/powerpc32/strlen.S +++ /dev/null @@ -1,190 +0,0 @@ -/* Optimized strlen implementation for PowerPC. - Copyright (C) 1997-2017 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 Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 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 - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - <http://www.gnu.org/licenses/>. */ - -#include <sysdep.h> - -/* 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. You get 0x80 in bytes that - match, but possibly false 0x80 matches in the next more significant - byte to a true match due to carries. For little-endian this is - of no consequence since the least significant match is the one - we're interested in, but big-endian needs method 2 to find which - byte matches. - - 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. */ - -/* int [r3] strlen (char *s [r3]) */ - -ENTRY (strlen) - -#define rTMP4 r0 -#define rRTN r3 /* incoming STR arg, outgoing result */ -#define rSTR r4 /* current string position */ -#define rPADN r5 /* number of padding bits we prepend to the - string to make it start at a word boundary */ -#define rFEFE r6 /* constant 0xfefefeff (-0x01010101) */ -#define r7F7F r7 /* constant 0x7f7f7f7f */ -#define rWORD1 r8 /* current string word */ -#define rWORD2 r9 /* next string word */ -#define rMASK r9 /* mask for first string word */ -#define rTMP1 r10 -#define rTMP2 r11 -#define rTMP3 r12 - - - clrrwi rSTR, rRTN, 2 - lis r7F7F, 0x7f7f - rlwinm rPADN, rRTN, 3, 27, 28 - lwz rWORD1, 0(rSTR) - li rMASK, -1 - addi r7F7F, r7F7F, 0x7f7f -/* We use method (2) on the first two words, because rFEFE isn't - required which reduces setup overhead. Also gives a faster return - for small strings on big-endian due to needing to recalculate with - method (2) anyway. */ -#ifdef __LITTLE_ENDIAN__ - slw rMASK, rMASK, rPADN -#else - srw rMASK, rMASK, rPADN -#endif - and rTMP1, r7F7F, rWORD1 - or rTMP2, r7F7F, rWORD1 - add rTMP1, rTMP1, r7F7F - nor rTMP3, rTMP2, rTMP1 - and. rTMP3, rTMP3, rMASK - mtcrf 0x01, rRTN - bne L(done0) - lis rFEFE, -0x101 - addi rFEFE, rFEFE, -0x101 -/* Are we now aligned to a doubleword boundary? */ - bt 29, L(loop) - -/* Handle second word of pair. */ -/* Perhaps use method (1) here for little-endian, saving one instruction? */ - lwzu rWORD1, 4(rSTR) - and rTMP1, r7F7F, rWORD1 - or rTMP2, r7F7F, rWORD1 - add rTMP1, rTMP1, r7F7F - nor. rTMP3, rTMP2, rTMP1 - bne L(done0) - -/* The loop. */ - -L(loop): - lwz rWORD1, 4(rSTR) - lwzu rWORD2, 8(rSTR) - add rTMP1, rFEFE, rWORD1 - nor rTMP2, r7F7F, rWORD1 - and. rTMP1, rTMP1, rTMP2 - add rTMP3, rFEFE, rWORD2 - nor rTMP4, r7F7F, rWORD2 - bne L(done1) - and. rTMP3, rTMP3, rTMP4 - beq L(loop) - -#ifndef __LITTLE_ENDIAN__ - and rTMP1, r7F7F, rWORD2 - add rTMP1, rTMP1, r7F7F - andc rTMP3, rTMP4, rTMP1 - b L(done0) - -L(done1): - and rTMP1, r7F7F, rWORD1 - subi rSTR, rSTR, 4 - add rTMP1, rTMP1, r7F7F - andc rTMP3, rTMP2, rTMP1 - -/* When we get to here, rSTR points to the first word in the string that - contains a zero byte, and rTMP3 has 0x80 for bytes that are zero, - and 0x00 otherwise. */ -L(done0): - cntlzw rTMP3, rTMP3 - subf rTMP1, rRTN, rSTR - srwi rTMP3, rTMP3, 3 - add rRTN, rTMP1, rTMP3 - blr -#else - -L(done0): - addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */ - andc rTMP1, rTMP1, rTMP3 - cntlzw rTMP1, rTMP1 /* Count bits not in the mask. */ - subf rTMP3, rRTN, rSTR - subfic rTMP1, rTMP1, 32-7 - srwi rTMP1, rTMP1, 3 - add rRTN, rTMP1, rTMP3 - blr - -L(done1): - addi rTMP3, rTMP1, -1 - andc rTMP3, rTMP3, rTMP1 - cntlzw rTMP3, rTMP3 - subf rTMP1, rRTN, rSTR - subfic rTMP3, rTMP3, 32-7-32 - srawi rTMP3, rTMP3, 3 - add rRTN, rTMP1, rTMP3 - blr -#endif - -END (strlen) -libc_hidden_builtin_def (strlen) |