176 lines
4.6 KiB
ArmAsm
176 lines
4.6 KiB
ArmAsm
/* Optimized strnlen implementation for PowerPC32/POWER7 using cmpb insn.
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Copyright (C) 2010-2022 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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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* int [r3] strnlen (char *s [r3], int size [r4]) */
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.machine power7
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ENTRY (__strnlen)
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CALL_MCOUNT
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dcbt 0,r3
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clrrwi r8,r3,2 /* Align the address to word boundary. */
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add r7,r3,r4 /* Calculate the last acceptable address. */
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cmplwi r4,16
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li r0,0 /* Word with null chars. */
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addi r7,r7,-1
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ble L(small_range)
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rlwinm r6,r3,3,27,28 /* Calculate padding. */
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lwz r12,0(r8) /* Load word from memory. */
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cmpb r10,r12,r0 /* Check for null bytes in DWORD1. */
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#ifdef __LITTLE_ENDIAN__
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srw r10,r10,r6
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slw r10,r10,r6
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#else
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slw r10,r10,r6
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srw r10,r10,r6
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#endif
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cmplwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
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bne cr7,L(done)
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clrrwi r7,r7,2 /* Address of last word. */
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mtcrf 0x01,r8
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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_setup)
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/* Handle WORD2 of pair. */
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lwzu r12,4(r8)
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cmpb r10,r12,r0
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cmplwi cr7,r10,0
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bne cr7,L(done)
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L(loop_setup):
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/* The last word we want to read in the loop below is the one
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containing the last byte of the string, ie. the word at
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(s + size - 1) & ~3, or r7. The first word read is at
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r8 + 4, we read 2 * cnt words, so the last word read will
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be at r8 + 4 + 8 * cnt - 4. Solving for cnt gives
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cnt = (r7 - r8) / 8 */
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sub r5,r7,r8
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srwi r6,r5,3 /* Number of loop iterations. */
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mtctr r6 /* Setup the counter. */
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/* Main loop to look for the null byte in the string. Since
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it's a 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(r8)
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lwzu r11,8(r8)
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cmpb r10,r12,r0
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cmpb r9,r11,r0
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or r5,r9,r10 /* Merge everything in one word. */
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cmplwi cr7,r5,0
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bne cr7,L(found)
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bdnz L(loop)
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/* We may have one more word to read. */
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cmplw cr6,r8,r7
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beq cr6,L(end_max)
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lwzu r12,4(r8)
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cmpb r10,r12,r0
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cmplwi cr6,r10,0
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bne cr6,L(done)
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L(end_max):
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mr r3,r4
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blr
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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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.align 4
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L(found):
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cmplwi cr6,r10,0
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addi r8,r8,-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 r8,r8,4
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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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We need to make sure the null char is *before* the end of the
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range. */
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L(done):
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#ifdef __LITTLE_ENDIAN__
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addi r0,r10,-1
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andc r0,r0,r10
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popcntw r0,r0
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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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sub r3,r8,r3
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srwi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
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add r3,r3,r0 /* Length until the match. */
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cmplw r3,r4
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blelr
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mr r3,r4
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blr
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/* Deals with size <= 16. */
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.align 4
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L(small_range):
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cmplwi r4,0
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beq L(end_max)
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clrrwi r7,r7,2 /* Address of last word. */
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rlwinm r6,r3,3,27,28 /* Calculate padding. */
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lwz r12,0(r8) /* Load word from memory. */
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cmpb r10,r12,r0 /* Check for null bytes in WORD1. */
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#ifdef __LITTLE_ENDIAN__
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srw r10,r10,r6
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slw r10,r10,r6
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#else
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slw r10,r10,r6
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srw r10,r10,r6
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#endif
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cmplwi cr7,r10,0
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bne cr7,L(done)
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cmplw r8,r7
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beq L(end_max)
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.p2align 5
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L(loop_small):
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lwzu r12,4(r8)
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cmpb r10,r12,r0
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cmplwi cr6,r10,0
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bne cr6,L(done)
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cmplw r8,r7
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bne L(loop_small)
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mr r3,r4
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blr
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END (__strnlen)
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libc_hidden_def (__strnlen)
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weak_alias (__strnlen, strnlen)
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libc_hidden_builtin_def (strnlen)
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