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authorRoland McGrath <roland@gnu.org>2002-09-17 23:50:03 +0000
committerRoland McGrath <roland@gnu.org>2002-09-17 23:50:03 +0000
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treec7d291182781c1534a03528b33d417983b8d2e54 /sysdeps/powerpc/powerpc64/strlen.S
parent81cb0d8214c425e356c3f79b4b024caab36540b8 (diff)
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2002-09-17 Steven Munroe <sjmunroe@us.ibm.com>
Ported to PowerPC64 running Linux. * sysdeps/powerpc/powerpc64/Dist: New file. * sysdeps/powerpc/powerpc64/Implies: New file. * sysdeps/powerpc/powerpc64/Makefile: New file. * sysdeps/powerpc/powerpc64/__longjmp.S: New file. * sysdeps/powerpc/powerpc64/atomicity.h: New file. * sysdeps/powerpc/powerpc64/backtrace.c: New file. * sysdeps/powerpc/powerpc64/bp-asm.h: New file. * sysdeps/powerpc/powerpc64/bsd-_setjmp.S: New file. * sysdeps/powerpc/powerpc64/bsd-setjmp.S: New file. * sysdeps/powerpc/powerpc64/dl-dtprocnum.h: New file. * sysdeps/powerpc/powerpc64/dl-lookupcfg.h: New file. * sysdeps/powerpc/powerpc64/dl-machine.c: New file. * sysdeps/powerpc/powerpc64/dl-machine.h: New file. * sysdeps/powerpc/powerpc64/memset.S: New file. * sysdeps/powerpc/powerpc64/ppc-mcount.S: New file. * sysdeps/powerpc/powerpc64/register-dump.h: New file. * sysdeps/powerpc/powerpc64/setjmp.S: New file. * sysdeps/powerpc/powerpc64/stpcpy.S: New file. * sysdeps/powerpc/powerpc64/strchr.S: New file. * sysdeps/powerpc/powerpc64/strcmp.S: New file. * sysdeps/powerpc/powerpc64/strcpy.S: New file. * sysdeps/powerpc/powerpc64/strlen.S: New file. * sysdeps/powerpc/powerpc64/elf/bzero.S: New file. * sysdeps/powerpc/powerpc64/elf/start.S: New file. * sysdeps/powerpc/powerpc64/fpu/s_copysign.S: New file. * sysdeps/powerpc/powerpc64/fpu/s_copysignf.S: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/Versions: New File. * sysdeps/unix/sysv/linux/powerpc/powerpc64/brk.S: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/glob64.c: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/socket.S: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/syscalls.list: New file. * sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h: New file.
Diffstat (limited to 'sysdeps/powerpc/powerpc64/strlen.S')
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diff --git a/sysdeps/powerpc/powerpc64/strlen.S b/sysdeps/powerpc/powerpc64/strlen.S
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+/* Optimized strlen implementation for PowerPC64.
+ Copyright (C) 1997, 1999, 2000, 2002 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, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include <sysdep.h>
+#include <bp-sym.h>
+#include <bp-asm.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.
+
+ 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 (BP_SYM (strlen))
+
+#define rTMP1 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 rTMP2 r10
+#define rTMP3 r11
+#define rTMP4 r12
+
+ CHECK_BOUNDS_LOW (rRTN, rTMP1, rTMP2)
+
+ clrrdi rSTR, rRTN, 2
+ lis r7F7F, 0x7f7f
+ rlwinm rPADN, rRTN, 3, 27, 28
+ lwz rWORD1, 0(rSTR)
+ li rMASK, -1
+ addi r7F7F, r7F7F, 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 rMASK, rMASK, rPADN
+ and rTMP1, r7F7F, rWORD1
+ or rTMP2, r7F7F, rWORD1
+ add rTMP1, rTMP1, r7F7F
+ nor rTMP1, rTMP2, rTMP1
+ and. rWORD1, rTMP1, rMASK
+ mtcrf 0x01, rRTN
+ bne L(done0)
+ lis rFEFE, -0x101
+ addi rFEFE, rFEFE, -0x101
+ clrldi rFEFE,rFEFE,32 /* clear upper 32 */
+/* Are we now aligned to a doubleword boundary? */
+ bt 29, L(loop)
+
+/* Handle second word of pair. */
+ lwzu rWORD1, 4(rSTR)
+ and rTMP1, r7F7F, rWORD1
+ or rTMP2, r7F7F, rWORD1
+ add rTMP1, rTMP1, r7F7F
+ nor. rWORD1, rTMP2, rTMP1
+ clrldi. rWORD1,rWORD1,32 /* clear upper 32 */
+ 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
+ clrldi. rTMP1,rTMP1,32 /* clear upper 32 */
+ add rTMP3, rFEFE, rWORD2
+ nor rTMP4, r7F7F, rWORD2
+ bne L(done1)
+ and. rTMP1, rTMP3, rTMP4
+ clrldi. rTMP1,rTMP1,32 /* clear upper 32 */
+ beq L(loop)
+
+ and rTMP1, r7F7F, rWORD2
+ add rTMP1, rTMP1, r7F7F
+ andc rWORD1, rTMP4, rTMP1
+ b L(done0)
+
+L(done1):
+ and rTMP1, r7F7F, rWORD1
+ subi rSTR, rSTR, 4
+ add rTMP1, rTMP1, r7F7F
+ andc rWORD1, rTMP2, rTMP1
+
+/* When we get to here, rSTR points to the first word in the string that
+ contains a zero byte, and the most significant set bit in rWORD1 is in that
+ byte. */
+L(done0):
+ cntlzw rTMP3, rWORD1
+ subf rTMP1, rRTN, rSTR
+ srwi rTMP3, rTMP3, 3
+ add rRTN, rTMP1, rTMP3
+ /* GKM FIXME: check high bound. */
+ blr
+END (BP_SYM (strlen))