[PATCH 3/3] aarch64: Import memrchr.S

Sebastian Huber <[email protected]>
Newsgroups gmane.comp.lib.newlib
Message-ID <[email protected]> 
Import memrchr.S for AArch64 from:

https://github.com/ARM-software/optimized-routines

commit 88b050e7d88d8dff4ffda97d9cf13a1c1b448eb7
Author: Joe Ramsay <[email protected]>
Date:   Tue Jul 25 10:01:52 2023 +0100

    pl/math: Use width-agnostic intrinsic forms

    No effect on performance, but a small improvement in readability.
---
 newlib/Makefile.in                         |  56 +++++++++--
 newlib/libc/machine/aarch64/Makefile.inc   |   2 +
 newlib/libc/machine/aarch64/memrchr-stub.c |  11 ++
 newlib/libc/machine/aarch64/memrchr.S      | 112 +++++++++++++++++++++
 4 files changed, 173 insertions(+), 8 deletions(-)
 create mode 100644 newlib/libc/machine/aarch64/memrchr-stub.c
 create mode 100644 newlib/libc/machine/aarch64/memrchr.S

diff --git a/newlib/Makefile.in b/newlib/Makefile.in
index 4d2b5e7825..302dbeea29 100644
--- a/newlib/Makefile.in
+++ b/newlib/Makefile.in
@@ -594,6 +594,8 @@ check_PROGRAMS =
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memcpy.S \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memmove-stub.c \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memmove.S \
+@HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memrchr-stub.c \
+@HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memrchr.S \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memset-stub.c \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/memset.S \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/rawmemchr.S \
@@ -911,18 +913,18 @@ check_PROGRAMS =
 @NEWLIB_HW_FP_FALSE@am__append_136 = libm/math/math.tex
 @HAVE_LONG_DOUBLE_TRUE@am__append_137 = $(libm_common_lsrc)
 @HAVE_FPMATH_H_TRUE@@HAVE_LONG_DOUBLE_TRUE@am__append_138 = $(libm_ld_lsrc)
-@HAVE_FPMATH_H_TRUE@am__append_139 =
-@HAVE_FPMATH_H_TRUE@am__append_140 =
+@HAVE_FPMATH_H_TRUE@am__append_139 = 
+@HAVE_FPMATH_H_TRUE@am__append_140 = 
 @HAVE_LIBM_MACHINE_AARCH64_TRUE@am__append_141 = $(libm_machine_aarch64_src)
 @HAVE_LIBM_MACHINE_AARCH64_TRUE@@HAVE_LONG_DOUBLE_TRUE@am__append_142 = $(libm_ld128_lsrc)
-@HAVE_LIBM_MACHINE_AARCH64_TRUE@am__append_143 =
-@HAVE_LIBM_MACHINE_AARCH64_TRUE@am__append_144 =
+@HAVE_LIBM_MACHINE_AARCH64_TRUE@am__append_143 = 
+@HAVE_LIBM_MACHINE_AARCH64_TRUE@am__append_144 = 
 @HAVE_LIBM_MACHINE_AMDGCN_TRUE@am__append_145 = $(libm_machine_amdgcn_src)
 @HAVE_LIBM_MACHINE_ARM_TRUE@am__append_146 = $(libm_machine_arm_src)
 @HAVE_LIBM_MACHINE_I386_TRUE@am__append_147 = $(libm_machine_i386_src)
 @HAVE_LIBM_MACHINE_I386_TRUE@@HAVE_LONG_DOUBLE_TRUE@am__append_148 = $(libm_ld80_lsrc)
-@HAVE_LIBM_MACHINE_I386_TRUE@am__append_149 =
-@HAVE_LIBM_MACHINE_I386_TRUE@am__append_150 =
+@HAVE_LIBM_MACHINE_I386_TRUE@am__append_149 = 
+@HAVE_LIBM_MACHINE_I386_TRUE@am__append_150 = 
 @HAVE_LIBM_MACHINE_MIPS_TRUE@am__append_151 = $(libm_machine_mips_src)
 @HAS_NDS32_FPU_SP_TRUE@@HAVE_LIBM_MACHINE_NDS32_TRUE@am__append_152 = libm/machine/nds32/wf_sqrt.S
 @HAS_NDS32_FPU_DP_TRUE@@HAVE_LIBM_MACHINE_NDS32_TRUE@am__append_153 = libm/machine/nds32/w_sqrt.S
@@ -934,8 +936,8 @@ check_PROGRAMS =
 @HAVE_LIBM_MACHINE_RISCV_TRUE@am__append_159 = $(libm_machine_riscv_src)
 @HAVE_LIBM_MACHINE_X86_64_TRUE@am__append_160 = $(libm_machine_x86_64_src)
 @HAVE_LIBM_MACHINE_X86_64_TRUE@@HAVE_LONG_DOUBLE_TRUE@am__append_161 = $(libm_ld80_lsrc)
-@HAVE_LIBM_MACHINE_X86_64_TRUE@am__append_162 =
-@HAVE_LIBM_MACHINE_X86_64_TRUE@am__append_163 =
+@HAVE_LIBM_MACHINE_X86_64_TRUE@am__append_162 = 
+@HAVE_LIBM_MACHINE_X86_64_TRUE@am__append_163 = 
 subdir = .
 ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
 am__aclocal_m4_deps = $(top_srcdir)/../config/depstand.m4 \
@@ -1831,6 +1833,8 @@ am__objects_51 = libc/ssp/libc_a-chk_fail.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memcpy.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memmove-stub.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memmove.$(OBJEXT) \
+@HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memrchr-stub.$(OBJEXT) \
+@HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memrchr.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memset-stub.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-memset.$(OBJEXT) \
 @HAVE_LIBC_MACHINE_AARCH64_TRUE@	libc/machine/aarch64/libc_a-rawmemchr.$(OBJEXT) \
@@ -7948,6 +7952,12 @@ libc/machine/aarch64/libc_a-memmove-stub.$(OBJEXT):  \
 libc/machine/aarch64/libc_a-memmove.$(OBJEXT):  \
 	libc/machine/aarch64/$(am__dirstamp) \
 	libc/machine/aarch64/$(DEPDIR)/$(am__dirstamp)
+libc/machine/aarch64/libc_a-memrchr-stub.$(OBJEXT):  \
+	libc/machine/aarch64/$(am__dirstamp) \
+	libc/machine/aarch64/$(DEPDIR)/$(am__dirstamp)
+libc/machine/aarch64/libc_a-memrchr.$(OBJEXT):  \
+	libc/machine/aarch64/$(am__dirstamp) \
+	libc/machine/aarch64/$(DEPDIR)/$(am__dirstamp)
 libc/machine/aarch64/libc_a-memset-stub.$(OBJEXT):  \
 	libc/machine/aarch64/$(am__dirstamp) \
 	libc/machine/aarch64/$(DEPDIR)/$(am__dirstamp)
@@ -12588,6 +12598,8 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memcpy.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memmove-stub.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memmove.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memset-stub.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-memset.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@libc/machine/aarch64/$(DEPDIR)/libc_a-rawmemchr-stub.Po@am__quote@
@@ -16547,6 +16559,20 @@ libc/machine/aarch64/libc_a-memmove.obj: libc/machine/aarch64/memmove.S
 @AMDEP_TRUE@@am__fastdepCCAS_FALSE@	DEPDIR=$(DEPDIR) $(CCASDEPMODE) $(depcomp) @AMDEPBACKSLASH@
 @am__fastdepCCAS_FALSE@	$(AM_V_CPPAS@am__nodep@)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -c -o libc/machine/aarch64/libc_a-memmove.obj `if test -f 'libc/machine/aarch64/memmove.S'; then $(CYGPATH_W) 'libc/machine/aarch64/memmove.S'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memmove.S'; fi`
 
+libc/machine/aarch64/libc_a-memrchr.o: libc/machine/aarch64/memrchr.S
+@am__fastdepCCAS_TRUE@	$(AM_V_CPPAS)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -MT libc/machine/aarch64/libc_a-memrchr.o -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Tpo -c -o libc/machine/aarch64/libc_a-memrchr.o `test -f 'libc/machine/aarch64/memrchr.S' || echo '$(srcdir)/'`libc/machine/aarch64/memrchr.S
+@am__fastdepCCAS_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Po
+@AMDEP_TRUE@@am__fastdepCCAS_FALSE@	$(AM_V_CPPAS)source='libc/machine/aarch64/memrchr.S' object='libc/machine/aarch64/libc_a-memrchr.o' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCCAS_FALSE@	DEPDIR=$(DEPDIR) $(CCASDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCCAS_FALSE@	$(AM_V_CPPAS@am__nodep@)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -c -o libc/machine/aarch64/libc_a-memrchr.o `test -f 'libc/machine/aarch64/memrchr.S' || echo '$(srcdir)/'`libc/machine/aarch64/memrchr.S
+
+libc/machine/aarch64/libc_a-memrchr.obj: libc/machine/aarch64/memrchr.S
+@am__fastdepCCAS_TRUE@	$(AM_V_CPPAS)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -MT libc/machine/aarch64/libc_a-memrchr.obj -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Tpo -c -o libc/machine/aarch64/libc_a-memrchr.obj `if test -f 'libc/machine/aarch64/memrchr.S'; then $(CYGPATH_W) 'libc/machine/aarch64/memrchr.S'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memrchr.S'; fi`
+@am__fastdepCCAS_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr.Po
+@AMDEP_TRUE@@am__fastdepCCAS_FALSE@	$(AM_V_CPPAS)source='libc/machine/aarch64/memrchr.S' object='libc/machine/aarch64/libc_a-memrchr.obj' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCCAS_FALSE@	DEPDIR=$(DEPDIR) $(CCASDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCCAS_FALSE@	$(AM_V_CPPAS@am__nodep@)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -c -o libc/machine/aarch64/libc_a-memrchr.obj `if test -f 'libc/machine/aarch64/memrchr.S'; then $(CYGPATH_W) 'libc/machine/aarch64/memrchr.S'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memrchr.S'; fi`
+
 libc/machine/aarch64/libc_a-memset.o: libc/machine/aarch64/memset.S
 @am__fastdepCCAS_TRUE@	$(AM_V_CPPAS)$(CCAS) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CCASFLAGS) $(CCASFLAGS) -MT libc/machine/aarch64/libc_a-memset.o -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memset.Tpo -c -o libc/machine/aarch64/libc_a-memset.o `test -f 'libc/machine/aarch64/memset.S' || echo '$(srcdir)/'`libc/machine/aarch64/memset.S
 @am__fastdepCCAS_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memset.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memset.Po
@@ -32649,6 +32675,20 @@ libc/machine/aarch64/libc_a-memmove-stub.obj: libc/machine/aarch64/memmove-stub.
 @AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
 @am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -c -o libc/machine/aarch64/libc_a-memmove-stub.obj `if test -f 'libc/machine/aarch64/memmove-stub.c'; then $(CYGPATH_W) 'libc/machine/aarch64/memmove-stub.c'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memmove-stub.c'; fi`
 
+libc/machine/aarch64/libc_a-memrchr-stub.o: libc/machine/aarch64/memrchr-stub.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -MT libc/machine/aarch64/libc_a-memrchr-stub.o -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Tpo -c -o libc/machine/aarch64/libc_a-memrchr-stub.o `test -f 'libc/machine/aarch64/memrchr-stub.c' || echo '$(srcdir)/'`libc/machine/aarch64/memrchr-stub.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Po
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='libc/machine/aarch64/memrchr-stub.c' object='libc/machine/aarch64/libc_a-memrchr-stub.o' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -c -o libc/machine/aarch64/libc_a-memrchr-stub.o `test -f 'libc/machine/aarch64/memrchr-stub.c' || echo '$(srcdir)/'`libc/machine/aarch64/memrchr-stub.c
+
+libc/machine/aarch64/libc_a-memrchr-stub.obj: libc/machine/aarch64/memrchr-stub.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -MT libc/machine/aarch64/libc_a-memrchr-stub.obj -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Tpo -c -o libc/machine/aarch64/libc_a-memrchr-stub.obj `if test -f 'libc/machine/aarch64/memrchr-stub.c'; then $(CYGPATH_W) 'libc/machine/aarch64/memrchr-stub.c'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memrchr-stub.c'; fi`
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memrchr-stub.Po
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='libc/machine/aarch64/memrchr-stub.c' object='libc/machine/aarch64/libc_a-memrchr-stub.obj' libtool=no @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -c -o libc/machine/aarch64/libc_a-memrchr-stub.obj `if test -f 'libc/machine/aarch64/memrchr-stub.c'; then $(CYGPATH_W) 'libc/machine/aarch64/memrchr-stub.c'; else $(CYGPATH_W) '$(srcdir)/libc/machine/aarch64/memrchr-stub.c'; fi`
+
 libc/machine/aarch64/libc_a-memset-stub.o: libc/machine/aarch64/memset-stub.c
 @am__fastdepCC_TRUE@	$(AM_V_CC)$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libc_a_CPPFLAGS) $(CPPFLAGS) $(libc_a_CFLAGS) $(CFLAGS) -MT libc/machine/aarch64/libc_a-memset-stub.o -MD -MP -MF libc/machine/aarch64/$(DEPDIR)/libc_a-memset-stub.Tpo -c -o libc/machine/aarch64/libc_a-memset-stub.o `test -f 'libc/machine/aarch64/memset-stub.c' || echo '$(srcdir)/'`libc/machine/aarch64/memset-stub.c
 @am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) libc/machine/aarch64/$(DEPDIR)/libc_a-memset-stub.Tpo libc/machine/aarch64/$(DEPDIR)/libc_a-memset-stub.Po
diff --git a/newlib/libc/machine/aarch64/Makefile.inc b/newlib/libc/machine/aarch64/Makefile.inc
index 063a2a84ae..c749b0d575 100644
--- a/newlib/libc/machine/aarch64/Makefile.inc
+++ b/newlib/libc/machine/aarch64/Makefile.inc
@@ -7,6 +7,8 @@ libc_a_SOURCES += \
 	%D%/memcpy.S \
 	%D%/memmove-stub.c \
 	%D%/memmove.S \
+	%D%/memrchr-stub.c \
+	%D%/memrchr.S \
 	%D%/memset-stub.c \
 	%D%/memset.S \
 	%D%/rawmemchr.S \
diff --git a/newlib/libc/machine/aarch64/memrchr-stub.c b/newlib/libc/machine/aarch64/memrchr-stub.c
new file mode 100644
index 0000000000..d80ca88ab0
--- /dev/null
+++ b/newlib/libc/machine/aarch64/memrchr-stub.c
@@ -0,0 +1,11 @@
+/* 
+ * Copyright (C) 2023 embedded brains GmbH & Co. KG
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#if defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED)
+#include "../../string/memrchr.c"
+#else
+/* See memrchr.S */
+#endif
diff --git a/newlib/libc/machine/aarch64/memrchr.S b/newlib/libc/machine/aarch64/memrchr.S
new file mode 100644
index 0000000000..817e96dfdd
--- /dev/null
+++ b/newlib/libc/machine/aarch64/memrchr.S
@@ -0,0 +1,112 @@
+/*
+ * memrchr - find last character in a memory zone.
+ *
+ * Copyright (c) 2020-2022, Arm Limited.
+ * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
+ */
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64, Advanced SIMD.
+ * MTE compatible.
+ */
+
+#include "asmdefs.h"
+
+#define srcin		x0
+#define chrin		w1
+#define cntin		x2
+#define result		x0
+
+#define src		x3
+#define cntrem		x4
+#define synd		x5
+#define shift		x6
+#define	tmp		x7
+#define end		x8
+#define endm1		x9
+
+#define vrepchr		v0
+#define qdata		q1
+#define vdata		v1
+#define vhas_chr	v2
+#define vend		v3
+#define dend		d3
+
+/*
+   Core algorithm:
+   For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits
+   per byte. We take 4 bits of every comparison byte with shift right and narrow
+   by 4 instruction. Since the bits in the nibble mask reflect the order in
+   which things occur in the original string, counting leading zeros identifies
+   exactly which byte matched.  */
+
+ENTRY (memrchr)
+	PTR_ARG (0)
+	add	end, srcin, cntin
+	sub	endm1, end, 1
+	bic	src, endm1, 15
+	cbz	cntin, L(nomatch)
+	ld1	{vdata.16b}, [src]
+	dup	vrepchr.16b, chrin
+	cmeq	vhas_chr.16b, vdata.16b, vrepchr.16b
+	neg	shift, end, lsl 2
+	shrn	vend.8b, vhas_chr.8h, 4		/* 128->64 */
+	fmov	synd, dend
+	lsl	synd, synd, shift
+	cbz	synd, L(start_loop)
+
+	clz	synd, synd
+	sub	result, endm1, synd, lsr 2
+	cmp	cntin, synd, lsr 2
+	csel	result, result, xzr, hi
+	ret
+
+	nop
+L(start_loop):
+	subs	cntrem, src, srcin
+	b.ls	L(nomatch)
+
+	/* Make sure that it won't overread by a 16-byte chunk */
+	sub	cntrem, cntrem, 1
+	tbz	cntrem, 4, L(loop32_2)
+	add	src, src, 16
+
+	.p2align 5
+L(loop32):
+	ldr	qdata, [src, -32]!
+	cmeq	vhas_chr.16b, vdata.16b, vrepchr.16b
+	umaxp	vend.16b, vhas_chr.16b, vhas_chr.16b		/* 128->64 */
+	fmov	synd, dend
+	cbnz	synd, L(end)
+
+L(loop32_2):
+	ldr	qdata, [src, -16]
+	subs	cntrem, cntrem, 32
+	cmeq	vhas_chr.16b, vdata.16b, vrepchr.16b
+	b.lo	L(end_2)
+	umaxp	vend.16b, vhas_chr.16b, vhas_chr.16b		/* 128->64 */
+	fmov	synd, dend
+	cbz	synd, L(loop32)
+L(end_2):
+	sub	src, src, 16
+L(end):
+	shrn	vend.8b, vhas_chr.8h, 4		/* 128->64 */
+	fmov	synd, dend
+
+	add	tmp, src, 15
+#ifdef __AARCH64EB__
+	rbit	synd, synd
+#endif
+	clz	synd, synd
+	sub	tmp, tmp, synd, lsr 2
+	cmp	tmp, srcin
+	csel	result, tmp, xzr, hs
+	ret
+
+L(nomatch):
+	mov	result, 0
+	ret
+
+END (memrchr)
+
-- 
2.35.3
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