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147 lines
4.2 KiB
ArmAsm
147 lines
4.2 KiB
ArmAsm
/* Optimized strchr implementation for PowerPC.
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Copyright (C) 1997-2014 Free Software Foundation, Inc.
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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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/* See strlen.s for comments on how this works. */
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/* char * [r3] strchr (const char *s [r3] , int c [r4] ) */
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ENTRY (strchr)
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#define rTMP1 r0
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#define rRTN r3 /* outgoing result */
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#define rSTR r8 /* current word pointer */
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#define rCHR r4 /* byte we're looking for, spread over the whole word */
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#define rWORD r5 /* the current word */
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#define rCLZB rCHR /* leading zero byte count */
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#define rFEFE r6 /* constant 0xfefefeff (-0x01010101) */
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#define r7F7F r7 /* constant 0x7f7f7f7f */
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#define rTMP2 r9
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#define rIGN r10 /* number of bits we should ignore in the first word */
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#define rMASK r11 /* mask with the bits to ignore set to 0 */
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#define rTMP3 r12
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#define rTMP4 rIGN
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#define rTMP5 rMASK
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rlwimi rCHR, rCHR, 8, 16, 23
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li rMASK, -1
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rlwimi rCHR, rCHR, 16, 0, 15
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rlwinm rIGN, rRTN, 3, 27, 28
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lis rFEFE, -0x101
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lis r7F7F, 0x7f7f
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clrrwi rSTR, rRTN, 2
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addi rFEFE, rFEFE, -0x101
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addi r7F7F, r7F7F, 0x7f7f
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/* Test the first (partial?) word. */
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lwz rWORD, 0(rSTR)
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#ifdef __LITTLE_ENDIAN__
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slw rMASK, rMASK, rIGN
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#else
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srw rMASK, rMASK, rIGN
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#endif
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orc rWORD, rWORD, rMASK
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add rTMP1, rFEFE, rWORD
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nor rTMP2, r7F7F, rWORD
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and. rTMP4, rTMP1, rTMP2
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xor rTMP3, rCHR, rWORD
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orc rTMP3, rTMP3, rMASK
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b L(loopentry)
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/* The loop. */
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L(loop):
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lwzu rWORD, 4(rSTR)
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and. rTMP5, rTMP1, rTMP2
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/* Test for 0. */
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add rTMP1, rFEFE, rWORD /* x - 0x01010101. */
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nor rTMP2, r7F7F, rWORD /* ~(x | 0x7f7f7f7f) == ~x & 0x80808080. */
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bne L(foundit)
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and. rTMP4, rTMP1, rTMP2 /* (x - 0x01010101) & ~x & 0x80808080. */
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/* Start test for the bytes we're looking for. */
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xor rTMP3, rCHR, rWORD
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L(loopentry):
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add rTMP1, rFEFE, rTMP3
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nor rTMP2, r7F7F, rTMP3
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beq L(loop)
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/* There is a zero byte in the word, but may also be a matching byte (either
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before or after the zero byte). In fact, we may be looking for a
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zero byte, in which case we return a match. */
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and. rTMP5, rTMP1, rTMP2
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li rRTN, 0
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beqlr
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/* At this point:
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rTMP5 bytes are 0x80 for each match of c, 0 otherwise.
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rTMP4 bytes are 0x80 for each match of 0, 0 otherwise.
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But there may be false matches in the next most significant byte from
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a true match due to carries. This means we need to recalculate the
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matches using a longer method for big-endian. */
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#ifdef __LITTLE_ENDIAN__
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addi rTMP1, rTMP5, -1
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andc rTMP1, rTMP1, rTMP5
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cntlzw rCLZB, rTMP1
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addi rTMP2, rTMP4, -1
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andc rTMP2, rTMP2, rTMP4
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cmplw rTMP1, rTMP2
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bgtlr
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subfic rCLZB, rCLZB, 32-7
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#else
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/* I think we could reduce this by two instructions by keeping the "nor"
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results from the loop for reuse here. See strlen.S tail. Similarly
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one instruction could be pruned from L(foundit). */
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and rFEFE, r7F7F, rWORD
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or rTMP5, r7F7F, rWORD
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and rTMP1, r7F7F, rTMP3
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or rTMP4, r7F7F, rTMP3
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add rFEFE, rFEFE, r7F7F
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add rTMP1, rTMP1, r7F7F
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nor rWORD, rTMP5, rFEFE
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nor rTMP2, rTMP4, rTMP1
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cntlzw rCLZB, rTMP2
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cmplw rWORD, rTMP2
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bgtlr
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#endif
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srwi rCLZB, rCLZB, 3
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add rRTN, rSTR, rCLZB
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blr
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L(foundit):
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#ifdef __LITTLE_ENDIAN__
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addi rTMP1, rTMP5, -1
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andc rTMP1, rTMP1, rTMP5
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cntlzw rCLZB, rTMP1
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subfic rCLZB, rCLZB, 32-7-32
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srawi rCLZB, rCLZB, 3
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#else
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and rTMP1, r7F7F, rTMP3
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or rTMP4, r7F7F, rTMP3
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add rTMP1, rTMP1, r7F7F
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nor rTMP2, rTMP4, rTMP1
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cntlzw rCLZB, rTMP2
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subi rSTR, rSTR, 4
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srwi rCLZB, rCLZB, 3
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#endif
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add rRTN, rSTR, rCLZB
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blr
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END (strchr)
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weak_alias (strchr, index)
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libc_hidden_builtin_def (strchr)
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