/*
   * Copyright (C) 2013 ARM Ltd.
   * Copyright (C) 2013 Linaro.
   *
   * This code is based on glibc cortex strings work originally authored by Linaro
   * and re-licensed under GPLv2 for the Linux kernel. The original code can
   * be found @
   *
   * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
   * files/head:/src/aarch64/
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * This program 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 General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  #include <linux/linkage.h>
  #include <asm/assembler.h>
  
  /*
  * compare memory areas(when two memory areas' offset are different,
  * alignment handled by the hardware)
  *
  * Parameters:
  *  x0 - const memory area 1 pointer
  *  x1 - const memory area 2 pointer
  *  x2 - the maximal compare byte length
  * Returns:
  *  x0 - a compare result, maybe less than, equal to, or greater than ZERO
  */
  
  /* Parameters and result.  */
  src1		.req	x0
  src2		.req	x1
  limit		.req	x2
  result		.req	x0
  
  /* Internal variables.  */
  data1		.req	x3
  data1w		.req	w3
  data2		.req	x4
  data2w		.req	w4
  has_nul		.req	x5
  diff		.req	x6
  endloop		.req	x7
  tmp1		.req	x8
  tmp2		.req	x9
  tmp3		.req	x10
  pos		.req	x11
  limit_wd	.req	x12
  mask		.req	x13
  
  ENTRY(memcmp)
  	cbz	limit, .Lret0
  	eor	tmp1, src1, src2
  	tst	tmp1, #7
  	b.ne	.Lmisaligned8
  	ands	tmp1, src1, #7
  	b.ne	.Lmutual_align
  	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
  	lsr	limit_wd, limit_wd, #3 /* Convert to Dwords.  */
  	/*
  	* The input source addresses are at alignment boundary.
  	* Directly compare eight bytes each time.
  	*/
  .Lloop_aligned:
  	ldr	data1, [src1], #8
  	ldr	data2, [src2], #8
  .Lstart_realigned:
  	subs	limit_wd, limit_wd, #1
  	eor	diff, data1, data2	/* Non-zero if differences found.  */
  	csinv	endloop, diff, xzr, cs	/* Last Dword or differences.  */
  	cbz	endloop, .Lloop_aligned
  
  	/* Not reached the limit, must have found a diff.  */
  	tbz	limit_wd, #63, .Lnot_limit
  
  	/* Limit % 8 == 0 => the diff is in the last 8 bytes. */
  	ands	limit, limit, #7
  	b.eq	.Lnot_limit
  	/*
  	* The remained bytes less than 8. It is needed to extract valid data
  	* from last eight bytes of the intended memory range.
  	*/
  	lsl	limit, limit, #3	/* bytes-> bits.  */
  	mov	mask, #~0
  CPU_BE( lsr	mask, mask, limit )
  CPU_LE( lsl	mask, mask, limit )
  	bic	data1, data1, mask
  	bic	data2, data2, mask
  
  	orr	diff, diff, mask
  	b	.Lnot_limit
  
  .Lmutual_align:
  	/*
  	* Sources are mutually aligned, but are not currently at an
  	* alignment boundary. Round down the addresses and then mask off
  	* the bytes that precede the start point.
  	*/
  	bic	src1, src1, #7
  	bic	src2, src2, #7
  	ldr	data1, [src1], #8
  	ldr	data2, [src2], #8
  	/*
  	* We can not add limit with alignment offset(tmp1) here. Since the
  	* addition probably make the limit overflown.
  	*/
  	sub	limit_wd, limit, #1/*limit != 0, so no underflow.*/
  	and	tmp3, limit_wd, #7
  	lsr	limit_wd, limit_wd, #3
  	add	tmp3, tmp3, tmp1
  	add	limit_wd, limit_wd, tmp3, lsr #3
  	add	limit, limit, tmp1/* Adjust the limit for the extra.  */
  
  	lsl	tmp1, tmp1, #3/* Bytes beyond alignment -> bits.*/
  	neg	tmp1, tmp1/* Bits to alignment -64.  */
  	mov	tmp2, #~0
  	/*mask off the non-intended bytes before the start address.*/
  CPU_BE( lsl	tmp2, tmp2, tmp1 )/*Big-endian.Early bytes are at MSB*/
  	/* Little-endian.  Early bytes are at LSB.  */
  CPU_LE( lsr	tmp2, tmp2, tmp1 )
  
  	orr	data1, data1, tmp2
  	orr	data2, data2, tmp2
  	b	.Lstart_realigned
  
  	/*src1 and src2 have different alignment offset.*/
  .Lmisaligned8:
  	cmp	limit, #8
  	b.lo	.Ltiny8proc /*limit < 8: compare byte by byte*/
  
  	and	tmp1, src1, #7
  	neg	tmp1, tmp1
  	add	tmp1, tmp1, #8/*valid length in the first 8 bytes of src1*/
  	and	tmp2, src2, #7
  	neg	tmp2, tmp2
  	add	tmp2, tmp2, #8/*valid length in the first 8 bytes of src2*/
  	subs	tmp3, tmp1, tmp2
  	csel	pos, tmp1, tmp2, hi /*Choose the maximum.*/
  
  	sub	limit, limit, pos
  	/*compare the proceeding bytes in the first 8 byte segment.*/
  .Ltinycmp:
  	ldrb	data1w, [src1], #1
  	ldrb	data2w, [src2], #1
  	subs	pos, pos, #1
  	ccmp	data1w, data2w, #0, ne  /* NZCV = 0b0000.  */
  	b.eq	.Ltinycmp
  	cbnz	pos, 1f /*diff occurred before the last byte.*/
  	cmp	data1w, data2w
  	b.eq	.Lstart_align
  1:
  	sub	result, data1, data2
  	ret
  
  .Lstart_align:
  	lsr	limit_wd, limit, #3
  	cbz	limit_wd, .Lremain8
  
  	ands	xzr, src1, #7
  	b.eq	.Lrecal_offset
  	/*process more leading bytes to make src1 aligned...*/
  	add	src1, src1, tmp3 /*backwards src1 to alignment boundary*/
  	add	src2, src2, tmp3
  	sub	limit, limit, tmp3
  	lsr	limit_wd, limit, #3
  	cbz	limit_wd, .Lremain8
  	/*load 8 bytes from aligned SRC1..*/
  	ldr	data1, [src1], #8
  	ldr	data2, [src2], #8
  
  	subs	limit_wd, limit_wd, #1
  	eor	diff, data1, data2  /*Non-zero if differences found.*/
  	csinv	endloop, diff, xzr, ne
  	cbnz	endloop, .Lunequal_proc
  	/*How far is the current SRC2 from the alignment boundary...*/
  	and	tmp3, tmp3, #7
  
  .Lrecal_offset:/*src1 is aligned now..*/
  	neg	pos, tmp3
  .Lloopcmp_proc:
  	/*
  	* Divide the eight bytes into two parts. First,backwards the src2
  	* to an alignment boundary,load eight bytes and compare from
  	* the SRC2 alignment boundary. If all 8 bytes are equal,then start
  	* the second part's comparison. Otherwise finish the comparison.
  	* This special handle can garantee all the accesses are in the
  	* thread/task space in avoid to overrange access.
  	*/
  	ldr	data1, [src1,pos]
  	ldr	data2, [src2,pos]
  	eor	diff, data1, data2  /* Non-zero if differences found.  */
  	cbnz	diff, .Lnot_limit
  
  	/*The second part process*/
  	ldr	data1, [src1], #8
  	ldr	data2, [src2], #8
  	eor	diff, data1, data2  /* Non-zero if differences found.  */
  	subs	limit_wd, limit_wd, #1
  	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
  	cbz	endloop, .Lloopcmp_proc
  .Lunequal_proc:
  	cbz	diff, .Lremain8
  
  /*There is differnence occured in the latest comparison.*/
  .Lnot_limit:
  /*
  * For little endian,reverse the low significant equal bits into MSB,then
  * following CLZ can find how many equal bits exist.
  */
  CPU_LE( rev	diff, diff )
  CPU_LE( rev	data1, data1 )
  CPU_LE( rev	data2, data2 )
  
  	/*
  	* The MS-non-zero bit of DIFF marks either the first bit
  	* that is different, or the end of the significant data.
  	* Shifting left now will bring the critical information into the
  	* top bits.
  	*/
  	clz	pos, diff
  	lsl	data1, data1, pos
  	lsl	data2, data2, pos
  	/*
  	* We need to zero-extend (char is unsigned) the value and then
  	* perform a signed subtraction.
  	*/
  	lsr	data1, data1, #56
  	sub	result, data1, data2, lsr #56
  	ret
  
  .Lremain8:
  	/* Limit % 8 == 0 =>. all data are equal.*/
  	ands	limit, limit, #7
  	b.eq	.Lret0
  
  .Ltiny8proc:
  	ldrb	data1w, [src1], #1
  	ldrb	data2w, [src2], #1
  	subs	limit, limit, #1
  
  	ccmp	data1w, data2w, #0, ne  /* NZCV = 0b0000. */
  	b.eq	.Ltiny8proc
  	sub	result, data1, data2
  	ret
  .Lret0:
  	mov	result, #0
  	ret
  ENDPIPROC(memcmp)