glibc/sysdeps/powerpc/powerpc32/power7/memchr.S

/* Optimized memchr implementation for PowerPC32/POWER7 using cmpb insn.
   Copyright (C) 2010-2013 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>
#include <bp-sym.h>
#include <bp-asm.h>

/* int [r3] memchr (char *s [r3], int byte [r4], int size [r5])  */
	.machine  power7
ENTRY (BP_SYM (__memchr))
	CALL_MCOUNT
	dcbt	0,r3
	clrrwi  r8,r3,2
	rlwimi	r4,r4,8,16,23
	rlwimi	r4,r4,16,0,15
	add	r7,r3,r5      /* Calculate the last acceptable address.  */
	cmplwi	r5,16
	ble	L(small_range)

	cmplw	cr7,r3,r7     /* Compare the starting address (r3) with the
				 ending address (r7).  If (r3 >= r7), the size
				 passed in is zero or negative.  */
	ble	cr7,L(proceed)

	li	r7,-1	      /* Artificially set our ending address (r7)
				 such that we will exit early. */
L(proceed):
	rlwinm	r6,r3,3,27,28 /* Calculate padding.  */
	cmpli	cr6,r6,0      /* cr6 == Do we have padding?  */
	lwz	r12,0(r8)     /* Load word from memory.  */
	cmpb	r10,r12,r4    /* Check for BYTEs in WORD1.  */
	beq	cr6,L(proceed_no_padding)
	slw	r10,r10,r6
	srw	r10,r10,r6
L(proceed_no_padding):
	cmplwi	cr7,r10,0     /* If r10 == 0, no BYTEs have been found.  */
	bne	cr7,L(done)

	/* Are we done already?  */
	addi	r9,r8,4
	cmplw	cr6,r9,r7
	bge	cr6,L(null)

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

	bt	29,L(loop_setup)

	/* Handle WORD2 of pair.  */
	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	cmplwi	cr7,r10,0
	bne	cr7,L(done)

	/* Are we done already?  */
	addi	r9,r8,4
	cmplw	cr6,r9,r7
	bge	cr6,L(null)

L(loop_setup):
	sub	r5,r7,r9
	srwi	r6,r5,3	      /* Number of loop iterations.  */
	mtctr	r6            /* Setup the counter.  */
	b	L(loop)
	/* Main loop to look for BYTE backwards in the string.  Since
	   it's a small loop (< 8 instructions), align it to 32-bytes.  */
	.p2align  5
L(loop):
	/* Load two words, compare and merge in a
	   single register for speed.  This is an attempt
	   to speed up the byte-checking process for bigger strings.  */
	lwz	r12,4(r8)
	lwzu	r11,8(r8)
	cmpb	r10,r12,r4
	cmpb	r9,r11,r4
	or	r5,r9,r10     /* Merge everything in one word.  */
	cmplwi	cr7,r5,0
	bne	cr7,L(found)
	bdnz	L(loop)

	/* We're here because the counter reached 0, and that means we
	   didn't have any matches for BYTE in the whole range.  */
	subi	r11,r7,4
	cmplw	cr6,r8,r11
	blt	cr6,L(loop_small)
	b	L(null)

	/* OK, one (or both) of the words contains BYTE.  Check
	   the first word and decrement the address in case the first
	   word really contains BYTE.  */
	.align	4
L(found):
	cmplwi	cr6,r10,0
	addi	r8,r8,-4
	bne	cr6,L(done)

	/* BYTE must be in the second word.  Adjust the address
	   again and move the result of cmpb to r10 so we can calculate the
	   pointer.  */

	mr	r10,r9
	addi	r8,r8,4

	/* r10 has the output of the cmpb instruction, that is, it contains
	   0xff in the same position as BYTE in the original
	   word from the string.  Use that to calculate the pointer.
	   We need to make sure BYTE is *before* the end of the range.  */
L(done):
	cntlzw	r0,r10	      /* Count leading zeroes before the match.  */
	srwi	r0,r0,3	      /* Convert leading zeroes to bytes.  */
	add	r3,r8,r0
	cmplw	r3,r7
	bge	L(null)
	blr

	.align	4
L(null):
	li	r3,0
	blr

/* Deals with size <= 16.  */
	.align	4
L(small_range):
	cmplwi	r5,0
	rlwinm	r6,r3,3,27,28 /* Calculate padding.  */
	beq	L(null)       /* This branch is for the cmplwi r5,0 above */
	lwz	r12,0(r8)     /* Load word from memory.  */
	cmplwi	cr6,r6,0      /* cr6 == Do we have padding?  */
	cmpb	r10,r12,r4    /* Check for BYTE in DWORD1.  */
	beq	cr6,L(small_no_padding)
	slw	r10,r10,r6
	srw	r10,r10,r6
L(small_no_padding):
	cmplwi	cr7,r10,0
	bne	cr7,L(done)

	/* Are we done already?  */
	addi    r9,r8,4
	cmplw	r9,r7
	bge	L(null)

L(loop_small):                /* loop_small has been unrolled.  */
	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,4
	cmplwi	cr6,r10,0
	cmplw	r9,r7
	bne	cr6,L(done)
	bge	L(null)

	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,4
	cmplwi	cr6,r10,0
	cmplw	r9,r7
	bne	cr6,L(done)
	bge	L(null)

	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,4
	cmplwi	cr6,r10,0
	cmplw	r9,r7
	bne	cr6,L(done)
	bge	L(null)

	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,4
	cmplwi	cr6,r10,0
	cmplw	r9,r7
	bne	cr6,L(done)
	bge	L(null)

	/* For most cases we will never get here.  Under some combinations of
	   padding + length there is a leftover word that still needs to be
	   checked.  */
	lwzu	r12,4(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,4
	cmplwi	cr6,r10,0
	bne	cr6,L(done)

	/* save a branch and exit directly */
	li	r3,0
	blr

END (BP_SYM (__memchr))
weak_alias (BP_SYM (__memchr), BP_SYM(memchr))
libc_hidden_builtin_def (memchr)