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

/* Optimized memchr implementation for PowerPC64/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>

/* int [r3] memchr (char *s [r3], int byte [r4], int size [r5])  */
	.machine  power7
ENTRY (__memchr)
	CALL_MCOUNT 2
	dcbt	0,r3
	clrrdi  r8,r3,3
	rlwimi	r4,r4,8,16,23
	rlwimi	r4,r4,16,0,15
	add	r7,r3,r5      /* Calculate the last acceptable address.  */
	cmpldi	r5,32
	insrdi  r4,r4,32,0
	ble	L(small_range)

	cmpld	cr7,r3,r7     /* Compare the starting address (r3) with the
				 ending address (r7).  If (r3 >= r7),
				 the size passed in was 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,r3,3,26,28 /* Calculate padding.  */
	cmpldi	cr6,r6,0      /* cr6 == Do we have padding?  */
	ld	r12,0(r8)     /* Load doubleword from memory.  */
	cmpb	r10,r12,r4    /* Check for BYTEs in DWORD1.  */
	beq	cr6,L(proceed_no_padding)
	sld	r10,r10,r6
	srd	r10,r10,r6
L(proceed_no_padding):
	cmpldi	cr7,r10,0     /* Does r10 indicate we got a hit?  */
	bne	cr7,L(done)

	/* See if we are at the last acceptable address yet.  */
	addi	r9,r8,8
	cmpld	cr6,r9,r7
	bge	cr6,L(null)

	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,r4
	cmpldi	cr7,r10,0
	bne	cr7,L(done)

	/* Are we done already?  */
	addi	r9,r8,8
	cmpld	cr6,r9,r7
	bge	cr6,L(null)

L(loop_setup):
	sub	r5,r7,r9
	srdi	r6,r5,4	      /* 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 doublewords, compare and merge in a
	   single register for speed.  This is an attempt
	   to speed up the byte-checking process for bigger strings.  */
	ld	r12,8(r8)
	ldu	r11,16(r8)
	cmpb	r10,r12,r4
	cmpb	r9,r11,r4
	or	r5,r9,r10     /* Merge everything in one doubleword.  */
	cmpldi	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,r7,8
	cmpld	cr6,r8,r11
	blt	cr6,L(loop_small)
	b	L(null)

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

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

	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 BYTE in the original
	   doubleword from the string.  Use that to calculate the pointer.
	   We need to make sure BYTE is *before* the end of the range.  */
L(done):
	cntlzd	r0,r10	      /* Count leading zeroes before the match.  */
	srdi	r0,r0,3	      /* Convert leading zeroes to bytes.  */
	add	r3,r8,r0
	cmpld	r3,r7
	bge	L(null)
	blr

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

/* Deals with size <= 32.  */
	.align	4
L(small_range):
	cmpldi	r5,0
	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
	beq	L(null)       /* This branch is for the cmpldi r5,0 above.  */
	ld	r12,0(r8)     /* Load word from memory.  */
	cmpldi	cr6,r6,0      /* cr6 == Do we have padding?  */
	cmpb	r10,r12,r4    /* Check for BYTE in DWORD1.  */
			      /* If no padding, skip the shifts.  */
	beq	cr6,L(small_no_padding)
	sld	r10,r10,r6
	srd	r10,r10,r6
L(small_no_padding):
	cmpldi	cr7,r10,0
	bne	cr7,L(done)

	/* Are we done already?  */
	addi    r9,r8,8
	cmpld	r9,r7
	bge	L(null)
	/* If we're not done, drop through into loop_small.  */

L(loop_small):                /* loop_small has been unrolled.  */
	ldu	r12,8(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,8
	cmpldi	cr6,r10,0
	cmpld	r9,r7
	bne	cr6,L(done)   /* Found something.  */
	bge	L(null)       /* Hit end of string (length).  */

	ldu	r12,8(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,8
	cmpldi	cr6,r10,0
	cmpld	r9,r7
	bne	cr6,L(done)   /* Found something.  */
	bge	L(null)

	ldu	r12,8(r8)
	subi	r11,r7,8
	cmpb	r10,r12,r4
	cmpldi	cr6,r10,0
	ori	r2,r2,0       /* Force a dispatch group.  */
	bne	cr6,L(done)

	cmpld	r8,r11        /* At end of range?  */
	bge	L(null)

	/* For most cases we will never get here.  Under some combinations of
	   padding + length there is a leftover double that still needs to be
	   checked.  */
	ldu	r12,8(r8)
	cmpb	r10,r12,r4
	addi	r9,r8,8
	cmpldi	cr6,r10,0
	cmpld	r9,r7
	bne	cr6,L(done)   /* Found something.  */

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


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