[AArch64] Add optimized strchrnul.

Here is an optimized implementation of __strchrnul.  The
simplification that we don't have to track precisely why the loop
terminates (match or end-of-string) means we have to do less work in
both setup and the core inner loop.  That means this should never be
slower than strchr.

As with strchr, the use of LD1 means we do not need different versions
for big-/little-endian.

1 files changed, 130 insertions, 0 deletions

diff --git a/sysdeps/aarch64/strchrnul.S b/sysdeps/aarch64/strchrnul.S
new file mode 100644
index 0000000..b98c2e9
--- /dev/null
+++ b/sysdeps/aarch64/strchrnul.S
@@ -0,0 +1,130 @@
+/* strchrnul - find a character or nul in a string
+
+   Copyright (C) 2014 Free Software Foundation, Inc.
+
+   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>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ * Neon Available.
+ */
+
+/* Arguments and results.  */
+#define srcin		x0
+#define chrin		w1
+
+#define result		x0
+
+/* Locals and temporaries.  */
+
+#define src		x2
+#define tmp1		x3
+#define wtmp2		w4
+#define tmp3		x5
+
+#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	v15
+#define vend1		v16
+
+/* 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 or 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.  */
+
+ENTRY (__strchrnul)
+	/* Magic constant 0x40100401 to allow us to identify which lane
+	   matches the termination condition.  */
+	mov	wtmp2, #0x0401
+	movk	wtmp2, #0x4010, lsl #16
+	dup	vrepchr.16b, chrin
+	bic	src, srcin, #31		/* Work with aligned 32-byte hunks.  */
+	dup	vrepmask.4s, wtmp2
+	ands	tmp1, srcin, #31
+	b.eq	L(loop)
+
+	/* 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
+	orr	vhas_chr1.16b, vhas_chr1.16b, vhas_nul1.16b
+	orr	vhas_chr2.16b, vhas_chr2.16b, vhas_nul2.16b
+	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+	lsl	tmp1, tmp1, #1
+	addp	vend1.16b, vhas_chr1.16b, vhas_chr2.16b	// 256->128
+	mov	tmp3, #~0
+	addp	vend1.16b, vend1.16b, vend1.16b		// 128->64
+	lsr	tmp1, tmp3, tmp1
+
+	mov	tmp3, vend1.2d[0]
+	bic	tmp1, tmp3, tmp1	// Mask padding bits.
+	cbnz	tmp1, L(tail)
+
+L(loop):
+	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
+	/* Use a fast check for the termination condition.  */
+	orr	vhas_chr1.16b, vhas_nul1.16b, vhas_chr1.16b
+	orr	vhas_chr2.16b, vhas_nul2.16b, vhas_chr2.16b
+	orr	vend1.16b, vhas_chr1.16b, vhas_chr2.16b
+	addp	vend1.2d, vend1.2d, vend1.2d
+	mov	tmp1, vend1.2d[0]
+	cbz	tmp1, L(loop)
+
+	/* Termination condition found.  Now need to establish exactly why
+	   we terminated.  */
+	and	vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
+	and	vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
+	addp	vend1.16b, vhas_chr1.16b, vhas_chr2.16b		// 256->128
+	addp	vend1.16b, vend1.16b, vend1.16b		// 128->64
+
+	mov	tmp1, vend1.2d[0]
+L(tail):
+	/* Count the trailing zeros, by bit reversing...  */
+	rbit	tmp1, tmp1
+	/* Re-bias source.  */
+	sub	src, src, #32
+	clz	tmp1, tmp1	/* ... and counting the leading zeros.  */
+	/* tmp1 is twice the offset into the fragment.  */
+	add	result, src, tmp1, lsr #1
+	ret
+
+END(__strchrnul)
+weak_alias (__strchrnul, strchrnul)