glibc/sysdeps/powerpc/powerpc64/power7/strnlen.S

/* Optimized strnlen implementation for PowerPC64/POWER7 using cmpb insn.
   Copyright (C) 2010-2017 Free Software Foundation, Inc.
   Contributed by Luis Machado <luisgpm@br.ibm.com>.
   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>

#ifndef STRNLEN
# define STRNLEN __strnlen
#endif

/* int [r3] strnlen (char *s [r3], int size [r4])  */
	.machine  power7
ENTRY_TOCLESS (STRNLEN)
	CALL_MCOUNT 2
	dcbt	0,r3
	clrrdi	r8,r3,3
	add	r7,r3,r4      /* Calculate the last acceptable address.  */
	cmpldi	r4,32
	li	r0,0	      /* Doubleword with null chars.  */
	addi	r7,r7,-1

	/* If we have less than 33 bytes to search, skip to a faster code.  */
	ble	L(small_range)

	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
	ld	r12,0(r8)     /* Load doubleword from memory.  */
	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
#ifdef __LITTLE_ENDIAN__
	srd	r10,r10,r6
	sld	r10,r10,r6
#else
	sld	r10,r10,r6
	srd	r10,r10,r6
#endif
	cmpldi	cr7,r10,0     /* If r10 == 0, no null's have been found.  */
	bne	cr7,L(done)

	clrrdi	r7,r7,3       /* Address of last doubleword.  */
	mtcrf   0x01,r8
	/* Are we now aligned to a quadword boundary?  If so, skip to
	   the main loop.  Otherwise, go through the alignment code.  */

	bt	28,L(loop_setup)

	/* Handle DWORD2 of pair.  */
	ldu	r12,8(r8)
	cmpb	r10,r12,r0
	cmpldi	cr7,r10,0
	bne	cr7,L(done)

L(loop_setup):
	/* The last dword we want to read in the loop below is the one
	   containing the last byte of the string, ie. the dword at
	   (s + size - 1) & ~7, or r7.  The first dword read is at
	   r8 + 8, we read 2 * cnt dwords, so the last dword read will
	   be at r8 + 8 + 16 * cnt - 8.  Solving for cnt gives
	   cnt = (r7 - r8) / 16  */
	sub	r5,r7,r8
	srdi	r6,r5,4	      /* Number of loop iterations.  */
	mtctr	r6	      /* Setup the counter.  */

	/* Main loop to look for the null byte in the string.  Since
	   it's a small loop (< 8 instructions), align it to 32-bytes.  */
	.p2align  5
L(loop):
	/* Load two doublewords, compare and merge in a
	   single register for speed.  This is an attempt
	   to speed up the null-checking process for bigger strings.  */

	ld	r12,8(r8)
	ldu	r11,16(r8)
	cmpb	r10,r12,r0
	cmpb	r9,r11,r0
	or	r5,r9,r10     /* Merge everything in one doubleword.  */
	cmpldi	cr7,r5,0
	bne	cr7,L(found)
	bdnz	L(loop)

	/* We may have one more dword to read.  */
	cmpld	cr6,r8,r7
	beq	cr6,L(end_max)

	ldu	r12,8(r8)
	cmpb	r10,r12,r0
	cmpldi	cr6,r10,0
	bne	cr6,L(done)

L(end_max):
	mr	r3,r4
	blr

	/* OK, one (or both) of the doublewords contains a null byte.  Check
	   the first doubleword and decrement the address in case the first
	   doubleword really contains a null byte.  */
	.align	4
L(found):
	cmpldi	cr6,r10,0
	addi	r8,r8,-8
	bne	cr6,L(done)

	/* The null byte must be in the second doubleword.  Adjust the address
	   again and move the result of cmpb to r10 so we can calculate the
	   length.  */

	mr	r10,r9
	addi	r8,r8,8

	/* r10 has the output of the cmpb instruction, that is, it contains
	   0xff in the same position as the null byte in the original
	   doubleword from the string.  Use that to calculate the length.
	   We need to make sure the null char is *before* the end of the
	   range.  */
L(done):
#ifdef __LITTLE_ENDIAN__
	addi	r0,r10,-1
	andc	r0,r0,r10
	popcntd	r0,r0
#else
	cntlzd	r0,r10	      /* Count leading zeros before the match.  */
#endif
	sub	r3,r8,r3
	srdi	r0,r0,3	      /* Convert leading/trailing zeros to bytes.  */
	add	r3,r3,r0      /* Length until the match.  */
	cmpld	r3,r4
	blelr
	mr	r3,r4
	blr

/* Deals with size <= 32.  */
	.align	4
L(small_range):
	cmpldi	r4,0
	beq	L(end_max)

	clrrdi	r7,r7,3       /* Address of last doubleword.  */

	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
	ld	r12,0(r8)     /* Load doubleword from memory.  */
	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
#ifdef __LITTLE_ENDIAN__
	srd	r10,r10,r6
	sld	r10,r10,r6
#else
	sld	r10,r10,r6
	srd	r10,r10,r6
#endif
	cmpldi	cr7,r10,0
	bne	cr7,L(done)

	cmpld	r8,r7
	beq	L(end_max)

	.p2align  5
L(loop_small):
	ldu	r12,8(r8)
	cmpb	r10,r12,r0
	cmpldi	cr6,r10,0
	bne	cr6,L(done)
	cmpld	r8,r7
	bne	L(loop_small)
	mr	r3,r4
	blr

END (STRNLEN)
libc_hidden_def (__strnlen)
weak_alias (__strnlen, strnlen)
libc_hidden_def (strnlen)