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http://sourceware.org/ml/libc-alpha/2013-08/msg00097.html This is the first of nine patches adding little-endian support to the existing optimised string and memory functions. I did spend some time with a power7 simulator looking at cycle by cycle behaviour for memchr, but most of these patches have not been run on cpu simulators to check that we are going as fast as possible. I'm sure PowerPC can do better. However, the little-endian support mostly leaves main loops unchanged, so I'm banking on previous authors having done a good job on big-endian.. As with most code you stare at long enough, I found some improvements for big-endian too. Little-endian support for strlen. Like most of the string functions, I leave the main word or multiple-word loops substantially unchanged, just needing to modify the tail. Removing the branch in the power7 functions is just a tidy. .align produces a branch anyway. Modifying regs in the non-power7 functions is to suit the new little-endian tail. * sysdeps/powerpc/powerpc64/power7/strlen.S (strlen): Add little-endian support. Don't branch over align. * sysdeps/powerpc/powerpc32/power7/strlen.S: Likewise. * sysdeps/powerpc/powerpc64/strlen.S (strlen): Add little-endian support. Rearrange tmp reg use to suit. Comment. * sysdeps/powerpc/powerpc32/strlen.S: Likewise.
103 lines
3.3 KiB
ArmAsm
103 lines
3.3 KiB
ArmAsm
/* Optimized strlen implementation for PowerPC32/POWER7 using cmpb insn.
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Copyright (C) 2010-2013 Free Software Foundation, Inc.
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Contributed by Luis Machado <luisgpm@br.ibm.com>.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* int [r3] strlen (char *s [r3]) */
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.machine power7
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ENTRY (strlen)
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CALL_MCOUNT
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dcbt 0,r3
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clrrwi r4,r3,2 /* Align the address to word boundary. */
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rlwinm r6,r3,3,27,28 /* Calculate padding. */
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li r0,0 /* Word with null chars to use with cmpb. */
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li r5,-1 /* MASK = 0xffffffffffffffff. */
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lwz r12,0(r4) /* Load word from memory. */
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#ifdef __LITTLE_ENDIAN__
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slw r5,r5,r6
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#else
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srw r5,r5,r6 /* MASK = MASK >> padding. */
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#endif
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orc r9,r12,r5 /* Mask bits that are not part of the string. */
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cmpb r10,r9,r0 /* Check for null bytes in WORD1. */
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cmpwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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bne cr7,L(done)
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mtcrf 0x01,r4
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/* Are we now aligned to a doubleword boundary? If so, skip to
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the main loop. Otherwise, go through the alignment code. */
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bt 29,L(loop)
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/* Handle WORD2 of pair. */
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lwzu r12,4(r4)
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cmpb r10,r12,r0
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cmpwi cr7,r10,0
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bne cr7,L(done)
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/* Main loop to look for the end of the string. Since it's a
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small loop (< 8 instructions), align it to 32-bytes. */
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.p2align 5
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L(loop):
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/* Load two words, compare and merge in a
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single register for speed. This is an attempt
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to speed up the null-checking process for bigger strings. */
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lwz r12, 4(r4)
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lwzu r11, 8(r4)
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cmpb r10,r12,r0
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cmpb r9,r11,r0
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or r8,r9,r10 /* Merge everything in one word. */
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cmpwi cr7,r8,0
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beq cr7,L(loop)
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/* OK, one (or both) of the words contains a null byte. Check
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the first word and decrement the address in case the first
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word really contains a null byte. */
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cmpwi cr6,r10,0
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addi r4,r4,-4
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bne cr6,L(done)
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/* The null byte must be in the second word. Adjust the address
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again and move the result of cmpb to r10 so we can calculate the
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length. */
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mr r10,r9
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addi r4,r4,4
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/* r10 has the output of the cmpb instruction, that is, it contains
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0xff in the same position as the null byte in the original
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word from the string. Use that to calculate the length. */
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L(done):
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#ifdef __LITTLE_ENDIAN__
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addi r9, r10, -1 /* Form a mask from trailing zeros. */
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andc r9, r9, r10
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popcntw r0, r9 /* Count the bits in the mask. */
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#else
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cntlzw r0,r10 /* Count leading zeros before the match. */
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#endif
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subf r5,r3,r4
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srwi r0,r0,3 /* Convert leading zeros to bytes. */
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add r3,r5,r0 /* Compute final length. */
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blr
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END (strlen)
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libc_hidden_builtin_def (strlen)
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