zyfeier commented on code in PR #8042:
URL: https://github.com/apache/nuttx/pull/8042#discussion_r1064322071
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libs/libc/machine/arm/armv8-m/gnu/arch_memcpy.S:
##########
@@ -0,0 +1,345 @@
+/****************************************************************************
+ * libs/libc/machine/arm/armv8-m/gnu/arch_memcpy.S
+ *
+ * Copyright (c) 2013 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:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. The name of the company may not be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY ARM LTD ``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 ARM LTD 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.
+ *
+ ****************************************************************************/
+
+#ifndef __ARM_FEATURE_MVE
+/* This memcpy routine is optimised for Cortex-M3/M4 cores with/without
+ unaligned access.
+
+ If compiled with GCC, this file should be enclosed within following
+ pre-processing check:
+ if defined (__ARM_ARCH_7M__) || defined (__ARM_ARCH_7EM__)
+
+ Prototype: void *memcpy (void *dst, const void *src, size_t count);
+
+ The job will be done in 5 steps.
+ Step 1: Align src/dest pointers, copy mis-aligned if fail to align both
+ Step 2: Repeatedly copy big block size of __OPT_BIG_BLOCK_SIZE
+ Step 3: Repeatedly copy big block size of __OPT_MID_BLOCK_SIZE
+ Step 4: Copy word by word
+ Step 5: Copy byte-to-byte
+
+ Tunable options:
+ __OPT_BIG_BLOCK_SIZE: Size of big block in words. Default to 64.
+ __OPT_MID_BLOCK_SIZE: Size of big block in words. Default to 16.
+ */
+#ifndef __OPT_BIG_BLOCK_SIZE
+#define __OPT_BIG_BLOCK_SIZE (4 * 16)
+#endif
+
+#ifndef __OPT_MID_BLOCK_SIZE
+#define __OPT_MID_BLOCK_SIZE (4 * 4)
+#endif
+
+#if __OPT_BIG_BLOCK_SIZE == 16
+#define BEGIN_UNROLL_BIG_BLOCK \
+ .irp offset, 0,4,8,12
+#elif __OPT_BIG_BLOCK_SIZE == 32
+#define BEGIN_UNROLL_BIG_BLOCK \
+ .irp offset, 0,4,8,12,16,20,24,28
+#elif __OPT_BIG_BLOCK_SIZE == 64
+#define BEGIN_UNROLL_BIG_BLOCK \
+ .irp offset, 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60
+#else
+#error "Illegal __OPT_BIG_BLOCK_SIZE"
+#endif
+
+#if __OPT_MID_BLOCK_SIZE == 8
+#define BEGIN_UNROLL_MID_BLOCK \
+ .irp offset, 0,4
+#elif __OPT_MID_BLOCK_SIZE == 16
+#define BEGIN_UNROLL_MID_BLOCK \
+ .irp offset, 0,4,8,12
+#else
+#error "Illegal __OPT_MID_BLOCK_SIZE"
+#endif
+
+#define END_UNROLL .endr
+#endif
+
+ .syntax unified
+ .text
+ .align 2
+ .global memcpy
+ .thumb
+ .thumb_func
+ .type memcpy, %function
+memcpy:
+ @ r0: dst
+ @ r1: src
+ @ r2: len
+#ifdef __ARM_FEATURE_MVE
+ mov r3, lr
+ wlstp.8 lr, r2, 2f
+ mov r2, r0
+1:
+ vldrb.8 q0, [r1], #16
+ vstrb.8 q0, [r2], #16
+ letp lr, 1b
+2:
+ bx r3
+#else
+#ifdef __ARM_FEATURE_UNALIGNED
+ /* In case of UNALIGNED access supported, ip is not used in
+ function body. */
+ mov ip, r0
+#else
+ push {r0}
+#endif
+ orr r3, r1, r0
+ ands r3, r3, #3
+ bne .Lmisaligned_copy
+
+.Lbig_block:
+ subs r2, __OPT_BIG_BLOCK_SIZE
+ blo .Lmid_block
+
+ /* Kernel loop for big block copy */
+ .align 2
+.Lbig_block_loop:
+ BEGIN_UNROLL_BIG_BLOCK
+#ifdef __ARM_ARCH_7EM__
Review Comment:
armv8-m use else branch.
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