src/newlib/newlib/libc/machine/aarch64/strrchr.S - stadia-controller/gcc-arm-none-eabi - Git at Google

 /*
    strrchr - find last instance of a character in a string

    Copyright (c) 2014, ARM 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 the company 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.  */

 #if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
 /* See strchr-stub.c  */
 #else

 /* Assumptions:
  *
  * ARMv8-a, AArch64
  * Neon Available.
  */

 /* Arguments and results.  */
 #define srcin		x0
 #define chrin		w1

 #define result		x0

 #define src		x2
 #define	tmp1		x3
 #define wtmp2		w4
 #define tmp3		x5
 #define src_match	x6
 #define src_offset	x7
 #define const_m1	x8
 #define tmp4		x9
 #define nul_match	x10
 #define chr_match	x11

 #define vrepchr		v0
 #define vdata1		v1
 #define vdata2		v2
 #define vhas_nul1	v3
 #define vhas_nul2	v4
 #define vhas_chr1	v5
 #define vhas_chr2	v6
 #define vrepmask_0	v7
 #define vrepmask_c	v16
 #define vend1		v17
 #define vend2		v18

 /* Core algorithm.

    For each 32-byte hunk we calculate a 64-bit syndrome value, with
    two bits per byte (LSB is always in bits 0 and 1, for both big
    and little-endian systems).  For each tuple, bit 0 is set iff
    the relevant byte matched the requested character; bit 1 is set
    iff the relevant byte matched the NUL end of string (we trigger
    off bit0 for the special case of looking for NUL).  Since the bits
    in the syndrome reflect exactly the order in which things occur
    in the original string a count_trailing_zeros() operation will
    identify exactly which byte is causing the termination, and why.  */

 /* Locals and temporaries.  */

 	.macro def_fn f p2align=0
 	.text
 	.p2align \p2align
 	.global \f
 	.type \f, %function
 \f:
 	.endm

 def_fn strrchr
 	/* Magic constant 0x40100401 to allow us to identify which lane
 	   matches the requested byte.  Magic constant 0x80200802 used
 	   similarly for NUL termination.  */
 	mov	wtmp2, #0x0401
 	movk	wtmp2, #0x4010, lsl #16
 	dup	vrepchr.16b, chrin
 	bic	src, srcin, #31		/* Work with aligned 32-byte hunks.  */
 	dup	vrepmask_c.4s, wtmp2
 	mov	src_offset, #0
 	ands	tmp1, srcin, #31
 	add	vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
 	b.eq	.Laligned

 	/* Input string is not 32-byte aligned.  Rather than forcing
 	   the padding bytes to a safe value, we calculate the syndrome
 	   for all the bytes, but then mask off those bits of the
 	   syndrome that are related to the padding.  */
 	ld1	{vdata1.16b, vdata2.16b}, [src], #32
 	neg	tmp1, tmp1
 	cmeq	vhas_nul1.16b, vdata1.16b, #0
 	cmeq	vhas_chr1.16b, vdata1.16b, vrepchr.16b
 	cmeq	vhas_nul2.16b, vdata2.16b, #0
 	cmeq	vhas_chr2.16b, vdata2.16b, vrepchr.16b
 	and	vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
 	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
 	and	vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
 	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
 	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b	// 256->128
 	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b	// 256->128
 	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b	// 128->64
 	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b	// 128->64
 	mov	nul_match, vhas_nul1.2d[0]
 	lsl	tmp1, tmp1, #1
 	mov	const_m1, #~0
 	mov	chr_match, vhas_chr1.2d[0]
 	lsr	tmp3, const_m1, tmp1

 	bic	nul_match, nul_match, tmp3	// Mask padding bits.
 	bic	chr_match, chr_match, tmp3	// Mask padding bits.
 	cbnz	nul_match, .Ltail

 .Lloop:
 	cmp	chr_match, #0
 	csel	src_match, src, src_match, ne
 	csel	src_offset, chr_match, src_offset, ne
 .Laligned:
 	ld1	{vdata1.16b, vdata2.16b}, [src], #32
 	cmeq	vhas_nul1.16b, vdata1.16b, #0
 	cmeq	vhas_chr1.16b, vdata1.16b, vrepchr.16b
 	cmeq	vhas_nul2.16b, vdata2.16b, #0
 	cmeq	vhas_chr2.16b, vdata2.16b, vrepchr.16b
 	addp	vend1.16b, vhas_nul1.16b, vhas_nul2.16b	// 256->128
 	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
 	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
 	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b	// 256->128
 	addp	vend1.16b, vend1.16b, vend1.16b	// 128->64
 	addp	vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b	// 128->64
 	mov	nul_match, vend1.2d[0]
 	mov	chr_match, vhas_chr1.2d[0]
 	cbz	nul_match, .Lloop

 	and	vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
 	and	vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
 	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
 	addp	vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
 	mov	nul_match, vhas_nul1.2d[0]

 .Ltail:
 	/* Work out exactly where the string ends.  */
 	sub	tmp4, nul_match, #1
 	eor	tmp4, tmp4, nul_match
 	ands	chr_match, chr_match, tmp4
 	/* And pick the values corresponding to the last match.  */
 	csel	src_match, src, src_match, ne
 	csel	src_offset, chr_match, src_offset, ne

 	/* Count down from the top of the syndrome to find the last match.  */
 	clz	tmp3, src_offset
 	/* Src_match points beyond the word containing the match, so we can
 	   simply subtract half the bit-offset into the syndrome.  Because
 	   we are counting down, we need to go back one more character.  */
 	add	tmp3, tmp3, #2
 	sub	result, src_match, tmp3, lsr #1
 	/* But if the syndrome shows no match was found, then return NULL.  */
 	cmp	src_offset, #0
 	csel	result, result, xzr, ne

 	ret

 	.size	strrchr, . - strrchr
 #endif
	/*
	strrchr - find last instance of a character in a string

	Copyright (c) 2014, ARM 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 the company 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. */

	#if (defined (__OPTIMIZE_SIZE__) \|\| defined (PREFER_SIZE_OVER_SPEED))
	/* See strchr-stub.c */
	#else

	/* Assumptions:
	*
	* ARMv8-a, AArch64
	* Neon Available.
	*/

	/* Arguments and results. */
	#define srcin x0
	#define chrin w1

	#define result x0

	#define src x2
	#define tmp1 x3
	#define wtmp2 w4
	#define tmp3 x5
	#define src_match x6
	#define src_offset x7
	#define const_m1 x8
	#define tmp4 x9
	#define nul_match x10
	#define chr_match x11

	#define vrepchr v0
	#define vdata1 v1
	#define vdata2 v2
	#define vhas_nul1 v3
	#define vhas_nul2 v4
	#define vhas_chr1 v5
	#define vhas_chr2 v6
	#define vrepmask_0 v7
	#define vrepmask_c v16
	#define vend1 v17
	#define vend2 v18

	/* Core algorithm.

	For each 32-byte hunk we calculate a 64-bit syndrome value, with
	two bits per byte (LSB is always in bits 0 and 1, for both big
	and little-endian systems). For each tuple, bit 0 is set iff
	the relevant byte matched the requested character; bit 1 is set
	iff the relevant byte matched the NUL end of string (we trigger
	off bit0 for the special case of looking for NUL). Since the bits
	in the syndrome reflect exactly the order in which things occur
	in the original string a count_trailing_zeros() operation will
	identify exactly which byte is causing the termination, and why. */

	/* Locals and temporaries. */

	.macro def_fn f p2align=0
	.text
	.p2align \p2align
	.global \f
	.type \f, %function
	\f:
	.endm

	def_fn strrchr
	/* Magic constant 0x40100401 to allow us to identify which lane
	matches the requested byte. Magic constant 0x80200802 used
	similarly for NUL termination. */
	mov wtmp2, #0x0401
	movk wtmp2, #0x4010, lsl #16
	dup vrepchr.16b, chrin
	bic src, srcin, #31 /* Work with aligned 32-byte hunks. */
	dup vrepmask_c.4s, wtmp2
	mov src_offset, #0
	ands tmp1, srcin, #31
	add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
	b.eq .Laligned

	/* Input string is not 32-byte aligned. Rather than forcing
	the padding bytes to a safe value, we calculate the syndrome
	for all the bytes, but then mask off those bits of the
	syndrome that are related to the padding. */
	ld1 {vdata1.16b, vdata2.16b}, [src], #32
	neg tmp1, tmp1
	cmeq vhas_nul1.16b, vdata1.16b, #0
	cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
	cmeq vhas_nul2.16b, vdata2.16b, #0
	cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
	and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
	and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
	and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
	and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
	addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
	addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
	addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b // 128->64
	addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
	mov nul_match, vhas_nul1.2d[0]
	lsl tmp1, tmp1, #1
	mov const_m1, #~0
	mov chr_match, vhas_chr1.2d[0]
	lsr tmp3, const_m1, tmp1

	bic nul_match, nul_match, tmp3 // Mask padding bits.
	bic chr_match, chr_match, tmp3 // Mask padding bits.
	cbnz nul_match, .Ltail

	.Lloop:
	cmp chr_match, #0
	csel src_match, src, src_match, ne
	csel src_offset, chr_match, src_offset, ne
	.Laligned:
	ld1 {vdata1.16b, vdata2.16b}, [src], #32
	cmeq vhas_nul1.16b, vdata1.16b, #0
	cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
	cmeq vhas_nul2.16b, vdata2.16b, #0
	cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
	addp vend1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
	and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
	and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
	addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
	addp vend1.16b, vend1.16b, vend1.16b // 128->64
	addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
	mov nul_match, vend1.2d[0]
	mov chr_match, vhas_chr1.2d[0]
	cbz nul_match, .Lloop

	and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
	and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
	addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
	addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
	mov nul_match, vhas_nul1.2d[0]

	.Ltail:
	/* Work out exactly where the string ends. */
	sub tmp4, nul_match, #1
	eor tmp4, tmp4, nul_match
	ands chr_match, chr_match, tmp4
	/* And pick the values corresponding to the last match. */
	csel src_match, src, src_match, ne
	csel src_offset, chr_match, src_offset, ne

	/* Count down from the top of the syndrome to find the last match. */
	clz tmp3, src_offset
	/* Src_match points beyond the word containing the match, so we can
	simply subtract half the bit-offset into the syndrome. Because
	we are counting down, we need to go back one more character. */
	add tmp3, tmp3, #2
	sub result, src_match, tmp3, lsr #1
	/* But if the syndrome shows no match was found, then return NULL. */
	cmp src_offset, #0
	csel result, result, xzr, ne

	ret

	.size strrchr, . - strrchr
	#endif