/* Copyright (c) 2010-2011, Linaro Limited
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

      * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.

      * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

      * Neither the name of Linaro Limited nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

   Written by Dave Gilbert <david.gilbert@linaro.org>

   This memchr routine is optimised on a Cortex-A9 and should work on
   all ARMv7 processors.   It has a fast path for short sizes, and has
   an optimised path for large data sets; the worst case is finding the
   match early in a large data set. */

/* Copyright (c) 2015 ARM Ltd.
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:
       * Redistributions of source code must retain the above copyright
	 notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above copyright
	 notice, this list of conditions and the following disclaimer in the
	 documentation and/or other materials provided with the distribution.
       * Neither the name of the Linaro nor the
	 names of its contributors may be used to endorse or promote products
	 derived from this software without specific prior written permission.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
   HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  */

// 2011-02-07 david.gilbert@linaro.org
//    Extracted from local git a5b438d861
// 2011-07-14 david.gilbert@linaro.org
//    Import endianness fix from local git ea786f1b
// 2011-10-11 david.gilbert@linaro.org
//    Import from cortex-strings bzr rev 63
//    Flip to ldrd (as suggested by Greta Yorsh)
//    Make conditional on CPU type
//    tidy

// This code requires armv6t2 or later.  Uses Thumb2.

#include <picolibc.h>

	.syntax unified

#include "arm_asm.h"

// NOTE: This ifdef MUST match the one in memchr-stub.c
#if defined (__ARM_NEON__) || defined (__ARM_NEON)
#if __ARM_ARCH >= 8 && __ARM_ARCH_PROFILE == 'R'
	.arch	armv8-r
#else
	.arch	armv7-a
#endif
	.fpu	neon


/* Arguments */
#define srcin		r0
#define chrin		r1
#define cntin		r2

/* Retval */
#define result		r0	/* Live range does not overlap with srcin */

/* Working registers */
#define src		r1	/* Live range does not overlap with chrin */
#define tmp		r3
#define synd		r0	/* No overlap with srcin or result */
#define soff		r12

/* Working NEON registers */
#define vrepchr		q0
#define vdata0		q1
#define vdata0_0	d2	/* Lower half of vdata0 */
#define vdata0_1	d3	/* Upper half of vdata0 */
#define vdata1		q2
#define vdata1_0	d4	/* Lower half of vhas_chr0 */
#define vdata1_1	d5	/* Upper half of vhas_chr0 */
#define vrepmask	q3
#define vrepmask0	d6
#define vrepmask1	d7
#define vend		q4
#define vend0		d8
#define vend1		d9

/*
 * Core algorithm:
 *
 * For each 32-byte chunk we calculate a 32-bit syndrome value, with one bit per
 * byte. Each bit is set if the relevant byte matched the requested character
 * and cleared otherwise. Since the bits in the syndrome reflect exactly the
 * order in which things occur in the original string, counting trailing zeros
 * allows to identify exactly which byte has matched.
 */

	.text
	.thumb_func
	.align 4
	.p2align 4,,15
	.global memchr
	.type memchr,%function

memchr:
	.cfi_sections .debug_frame
	.cfi_startproc
	/* Use a simple loop if there are less than 8 bytes to search.  */
	cmp	cntin, #7
	bhi	.Llargestr
	and	chrin, chrin, #0xff

.Lsmallstr:
	subs	cntin, cntin, #1
	blo	.Lnotfound	/* Return not found if reached end.  */
	ldrb	tmp, [srcin], #1
	cmp	tmp, chrin
	bne	.Lsmallstr	/* Loop again if not found.  */
	/* Otherwise fixup address and return.  */
	sub	result, result, #1
	bx	lr


.Llargestr:
	vdup.8	vrepchr, chrin	/* Duplicate char across all lanes. */
	/*
	 * Magic constant 0x8040201008040201 allows us to identify which lane
	 * matches the requested byte.
	 */
	movw	tmp, #0x0201
	movt	tmp, #0x0804
	lsl	soff, tmp, #4
	vmov	vrepmask0, tmp, soff
	vmov	vrepmask1, tmp, soff
	/* Work with aligned 32-byte chunks */
	bic	src, srcin, #31
	ands	soff, srcin, #31
	beq	.Lloopintro	/* Go straight to main loop if it's aligned. */

	/*
	 * Input string is not 32-byte aligned. We calculate the syndrome
	 * value for the aligned 32 bytes block containing the first bytes
	 * and mask the irrelevant part.
	 */
	vld1.8		{vdata0, vdata1}, [src:256]!
	sub		tmp, soff, #32
	adds		cntin, cntin, tmp
	vceq.i8		vdata0, vdata0, vrepchr
	vceq.i8		vdata1, vdata1, vrepchr
	vand		vdata0, vdata0, vrepmask
	vand		vdata1, vdata1, vrepmask
	vpadd.i8	vdata0_0, vdata0_0, vdata0_1
	vpadd.i8	vdata1_0, vdata1_0, vdata1_1
	vpadd.i8	vdata0_0, vdata0_0, vdata1_0
	vpadd.i8	vdata0_0, vdata0_0, vdata0_0
	vmov		synd, vdata0_0[0]

	/* Clear the soff lower bits */
	lsr		synd, synd, soff
	lsl		synd, synd, soff
	/* The first block can also be the last */
	bls		.Lmasklast
	/* Have we found something already? */
	cbnz		synd, .Ltail


.Lloopintro:
	vpush	{vend}
	/* 264/265 correspond to d8/d9 for q4 */
	.cfi_adjust_cfa_offset	16
	.cfi_rel_offset	264, 0
	.cfi_rel_offset	265, 8
	.p2align 3,,7
.Lloop:
	vld1.8		{vdata0, vdata1}, [src:256]!
	subs		cntin, cntin, #32
	vceq.i8		vdata0, vdata0, vrepchr
	vceq.i8		vdata1, vdata1, vrepchr
	/* If we're out of data we finish regardless of the result. */
	bls		.Lend
	/* Use a fast check for the termination condition. */
	vorr		vend, vdata0, vdata1
	vorr		vend0, vend0, vend1
	vmov		synd, tmp, vend0
	orrs		synd, synd, tmp
	/* We're not out of data, loop if we haven't found the character. */
	beq		.Lloop

.Lend:
	vpop		{vend}
	.cfi_adjust_cfa_offset	-16
	.cfi_restore	264
	.cfi_restore	265

	/* Termination condition found, let's calculate the syndrome value. */
	vand		vdata0, vdata0, vrepmask
	vand		vdata1, vdata1, vrepmask
	vpadd.i8	vdata0_0, vdata0_0, vdata0_1
	vpadd.i8	vdata1_0, vdata1_0, vdata1_1
	vpadd.i8	vdata0_0, vdata0_0, vdata1_0
	vpadd.i8	vdata0_0, vdata0_0, vdata0_0
	vmov		synd, vdata0_0[0]
	cbz		synd, .Lnotfound
	bhi		.Ltail


.Lmasklast:
	/* Clear the (-cntin) upper bits to avoid out-of-bounds matches. */
	neg	cntin, cntin
	lsl	synd, synd, cntin
	lsrs	synd, synd, cntin
	it	eq
	moveq	src, #0	/* If no match, set src to 0 so the retval is 0. */


.Ltail:
	/* Count the trailing zeros using bit reversing */
	rbit	synd, synd
	/* Compensate the last post-increment */
	sub	src, src, #32
	/* Count the leading zeros */
	clz	synd, synd
	/* Compute the potential result and return */
	add	result, src, synd
	bx	lr


.Lnotfound:
	/* Set result to NULL if not found and return */
	mov	result, #0
	bx	lr

	.cfi_endproc
	.size	memchr, . - memchr

#elif __ARM_ARCH_ISA_THUMB >= 2 && defined (__ARM_FEATURE_DSP)

#if __ARM_ARCH_PROFILE == 'M'
#if __ARM_ARCH >= 8
	/* keep config inherited from -march=.  */
#else
	.arch armv7e-m
#endif /* __ARM_ARCH >= 8 */
#else
	.arch armv6t2
#endif /* __ARM_ARCH_PROFILE == 'M' */

// this lets us check a flag in a 00/ff byte easily in either endianness
#ifdef __ARMEB__
#define CHARTSTMASK(c) 1<<(31-(c*8))
#else
#define CHARTSTMASK(c) 1<<(c*8)
#endif
	.text
	.thumb

// ---------------------------------------------------------------------------
	.thumb_func
	.align 2
	.p2align 4,,15
	.global memchr
	.type memchr,%function
	.fnstart
	.cfi_sections .debug_frame
	.cfi_startproc
memchr:
	// r0 = start of memory to scan
	// r1 = character to look for
	// r2 = length
	// returns r0 = pointer to character or NULL if not found
	prologue
	and	r1,r1,#0xff	// Don't trust the caller to pass a char

	cmp	r2,#16		// If short don't bother with anything clever
	blt	20f 

	tst	r0, #7		// If it's already aligned skip the next bit
	beq	10f

	// Work up to an aligned point
5:
	ldrb	r3, [r0],#1
	subs	r2, r2, #1
	cmp	r3, r1
	beq	50f		// If it matches exit found
	tst	r0, #7
	cbz	r2, 40f		// If we run off the end, exit not found
	bne	5b		// If not aligned yet then do next byte
	
10:
	// We are aligned, we know we have at least 8 bytes to work with
	push	{r4,r5,r6,r7}
	.cfi_adjust_cfa_offset 16
	.cfi_rel_offset 4, 0
	.cfi_rel_offset 5, 4
	.cfi_rel_offset 6, 8
	.cfi_rel_offset 7, 12
	orr	r1, r1, r1, lsl #8	// expand the match word across all bytes
	orr	r1, r1, r1, lsl #16
	bic	r4, r2, #7	// Number of double words to work with * 8
	mvns	r7, #0		// all F's
	movs	r3, #0
	
15:
	ldrd    r5,r6,[r0],#8
	subs	r4, r4, #8
	eor	r5,r5, r1	// r5,r6 have 00's where bytes match the target
	eor	r6,r6, r1
	uadd8	r5, r5, r7	// Par add 0xff - sets GE bits for bytes!=0
	sel	r5, r3, r7	// bytes are 00 for none-00 bytes,
				// or ff for 00 bytes - NOTE INVERSION
	uadd8	r6, r6, r7	// Par add 0xff - sets GE bits for bytes!=0
	sel	r6, r5, r7	// chained....bytes are 00 for none-00 bytes
				// or ff for 00 bytes - NOTE INVERSION
	cbnz	r6, 60f
	bne	15b		// (Flags from the subs above)

	pop	{r4,r5,r6,r7}
	.cfi_restore 7
	.cfi_restore 6
	.cfi_restore 5
	.cfi_restore 4
	.cfi_adjust_cfa_offset -16
	and	r1,r1,#0xff	// r1 back to a single character
	and	r2,r2,#7	// Leave the count remaining as the number
				// after the double words have been done
 
20:
	cbz	r2, 40f		// 0 length or hit the end already then not found

21:  // Post aligned section, or just a short call
	ldrb	r3,[r0],#1
	subs	r2,r2,#1
	eor	r3,r3,r1	// r3 = 0 if match - doesn't break flags from sub
	cbz	r3, 50f
	bne	21b		// on r2 flags

40:
	.cfi_remember_state
	movs	r0,#0		// not found
	epilogue

50:
	.cfi_restore_state
	.cfi_remember_state
	subs	r0,r0,#1	// found
	epilogue

60:  // We're here because the fast path found a hit 
     // now we have to track down exactly which word it was
	// r0 points to the start of the double word after the one tested
	// r5 has the 00/ff pattern for the first word, r6 has the chained value
	// This point is reached from cbnz midway through label 15 prior to
	// popping r4-r7 off the stack.  .cfi_restore_state alone disregards
	// this, so we manually correct this.
	.cfi_restore_state	// Standard post-prologue state
	.cfi_adjust_cfa_offset 16
	.cfi_rel_offset 4, 0
	.cfi_rel_offset 5, 4
	.cfi_rel_offset 6, 8
	.cfi_rel_offset 7, 12
	cmp	r5, #0
	itte	eq
	moveq	r5, r6		// the end is in the 2nd word
	subeq	r0,r0,#3	// Points to 2nd byte of 2nd word
	subne	r0,r0,#7	// or 2nd byte of 1st word

	// r0 currently points to the 2nd byte of the word containing the hit
	tst	r5, # CHARTSTMASK(0)	// 1st character
	bne	61f
	adds	r0,r0,#1
	tst	r5, # CHARTSTMASK(1)	// 2nd character
	ittt	eq
	addeq	r0,r0,#1
	tsteq	r5, # (3<<15)		// 2nd & 3rd character
	// If not the 3rd must be the last one
	addeq	r0,r0,#1

61:
	pop	{r4,r5,r6,r7}
	.cfi_restore 7
	.cfi_restore 6
	.cfi_restore 5
	.cfi_restore 4
	.cfi_adjust_cfa_offset -16
	subs	r0,r0,#1
	epilogue
	.cfi_endproc
	.cantunwind
	.fnend
#else
  /* Defined in memchr.c.  */
#endif
