[libc-commits] [libc] 2423ec5 - [libc] Add memmove implementation.
Cheng Wang via libc-commits
libc-commits at lists.llvm.org
Thu Jan 14 20:08:44 PST 2021
Author: Cheng Wang
Date: 2021-01-15T12:08:25+08:00
New Revision: 2423ec583761304f93b5d01493a26aeb11cb5b8f
URL: https://github.com/llvm/llvm-project/commit/2423ec583761304f93b5d01493a26aeb11cb5b8f
DIFF: https://github.com/llvm/llvm-project/commit/2423ec583761304f93b5d01493a26aeb11cb5b8f.diff
LOG: [libc] Add memmove implementation.
Use `memcpy` rather than copying bytes one by one, for there might be large
size structs to move.
Reviewed By: gchatelet, sivachandra
Differential Revision: https://reviews.llvm.org/D93195
Added:
libc/src/string/memmove.cpp
libc/src/string/memmove.h
libc/test/src/string/memmove_test.cpp
Modified:
libc/config/linux/aarch64/entrypoints.txt
libc/config/linux/x86_64/entrypoints.txt
libc/src/string/CMakeLists.txt
libc/test/src/string/CMakeLists.txt
Removed:
################################################################################
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 2b70cafd6fbf..4e20903ad260 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -30,6 +30,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.string.memchr
libc.src.string.memcmp
libc.src.string.memcpy
+ libc.src.string.memmove
libc.src.string.memset
libc.src.string.memrchr
libc.src.string.strcat
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 7c5367a9d528..d073e63d715f 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -52,6 +52,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.string.memchr
libc.src.string.memcmp
libc.src.string.memcpy
+ libc.src.string.memmove
libc.src.string.memrchr
libc.src.string.memset
libc.src.string.strcat
diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
index 683b85720c60..e40eeb16b907 100644
--- a/libc/src/string/CMakeLists.txt
+++ b/libc/src/string/CMakeLists.txt
@@ -66,6 +66,18 @@ add_entrypoint_object(
memcmp.h
)
+add_entrypoint_object(
+ memmove
+ SRCS
+ memmove.cpp
+ HDRS
+ memmove.h
+ DEPENDS
+ libc.include.unistd
+ libc.src.stdlib.abs_utils
+ libc.src.string.memcpy
+)
+
add_entrypoint_object(
strchr
SRCS
diff --git a/libc/src/string/memmove.cpp b/libc/src/string/memmove.cpp
new file mode 100644
index 000000000000..8958027d1d58
--- /dev/null
+++ b/libc/src/string/memmove.cpp
@@ -0,0 +1,61 @@
+//===-- Implementation of memmove -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/string/memmove.h"
+#include "src/__support/common.h"
+#include "src/stdlib/abs_utils.h"
+#include "src/string/memcpy.h"
+#include <stddef.h> // size_t, ptr
diff _t
+#include <unistd.h> // ssize_t
+
+namespace __llvm_libc {
+
+// src_m and dest_m might be the beginning or end.
+static inline void move_byte(unsigned char *dest_m, const unsigned char *src_m,
+ size_t count, ssize_t direction) {
+ for (ssize_t offset = 0; count; --count, offset += direction)
+ dest_m[offset] = src_m[offset];
+}
+
+LLVM_LIBC_FUNCTION(void *, memmove,
+ (void *dest, const void *src, size_t count)) {
+ unsigned char *dest_c = reinterpret_cast<unsigned char *>(dest);
+ const unsigned char *src_c = reinterpret_cast<const unsigned char *>(src);
+
+ // If the distance between src_c and dest_c is equal to or greater
+ // than count (integer_abs(src_c - dest_c) >= count), they would not overlap.
+ // e.g. greater equal overlapping
+ // [12345678] [12345678] [12345678]
+ // src_c: [_ab_____] [_ab_____] [_ab_____]
+ // dest_c:[_____yz_] [___yz___] [__yz____]
+
+ // Use memcpy if src_c and dest_c do not overlap.
+ if (__llvm_libc::integer_abs(src_c - dest_c) >= static_cast<ptr
diff _t>(count))
+ return __llvm_libc::memcpy(dest_c, src_c, count);
+
+ // Overlap cases.
+ // If dest_c starts before src_c (dest_c < src_c), copy forward(pointer add 1)
+ // from beginning to end.
+ // If dest_c starts after src_c (dest_c > src_c), copy backward(pointer add
+ // -1) from end to beginning.
+ // If dest_c and src_c start at the same address (dest_c == src_c),
+ // just return dest.
+ // e.g. forward backward
+ // *--> <--*
+ // src_c : [___abcde_] [_abcde___]
+ // dest_c: [_abc--___] [___--cde_]
+
+ // TODO: Optimize `move_byte(...)` function.
+ if (dest_c < src_c)
+ move_byte(dest_c, src_c, count, /*pointer add*/ 1);
+ if (dest_c > src_c)
+ move_byte(dest_c + count - 1, src_c + count - 1, count, /*pointer add*/ -1);
+ return dest;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/string/memmove.h b/libc/src/string/memmove.h
new file mode 100644
index 000000000000..6d24a59a23c2
--- /dev/null
+++ b/libc/src/string/memmove.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for memmove -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STRING_MEMMOVE_H
+#define LLVM_LIBC_SRC_STRING_MEMMOVE_H
+
+#include <stddef.h> // size_t
+
+namespace __llvm_libc {
+
+void *memmove(void *dest, const void *src, size_t count);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_MEMMOVE_H
diff --git a/libc/test/src/string/CMakeLists.txt b/libc/test/src/string/CMakeLists.txt
index 8202c699f20b..dbdad3ee6aef 100644
--- a/libc/test/src/string/CMakeLists.txt
+++ b/libc/test/src/string/CMakeLists.txt
@@ -62,6 +62,17 @@ add_libc_unittest(
libc.src.string.memcmp
)
+add_libc_unittest(
+ memmove_test
+ SUITE
+ libc_string_unittests
+ SRCS
+ memmove_test.cpp
+ DEPENDS
+ libc.src.string.memcmp
+ libc.src.string.memmove
+)
+
add_libc_unittest(
strchr_test
SUITE
diff --git a/libc/test/src/string/memmove_test.cpp b/libc/test/src/string/memmove_test.cpp
new file mode 100644
index 000000000000..88a0139d5ff8
--- /dev/null
+++ b/libc/test/src/string/memmove_test.cpp
@@ -0,0 +1,70 @@
+//===-- Unittests for memmove ---------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/string/memcmp.h"
+#include "src/string/memmove.h"
+#include "utils/CPP/ArrayRef.h"
+#include "utils/UnitTest/Test.h"
+
+class MemmoveTest : public __llvm_libc::testing::Test {
+public:
+ void check_memmove(void *dest, const void *src, size_t count, const void *str,
+ const __llvm_libc::cpp::ArrayRef<unsigned char> expected) {
+ void *result = __llvm_libc::memmove(dest, src, count);
+ // Making sure the pointer returned is same with dest.
+ EXPECT_EQ(result, dest);
+ // expected is designed according to str.
+ // dest and src might be part of str.
+ // Making sure the str is same with expected.
+ EXPECT_EQ(__llvm_libc::memcmp(str, expected.data(), expected.size()), 0);
+ }
+};
+
+TEST_F(MemmoveTest, MoveZeroByte) {
+ unsigned char dest[] = {'a', 'b'};
+ const unsigned char src[] = {'y', 'z'};
+ const unsigned char expected[] = {'a', 'b'};
+ check_memmove(dest, src, 0, dest, expected);
+}
+
+TEST_F(MemmoveTest, OverlapThatDestAndSrcPointToSameAddress) {
+ unsigned char str[] = {'a', 'b'};
+ const unsigned char expected[] = {'a', 'b'};
+ check_memmove(str, str, 1, str, expected);
+}
+
+TEST_F(MemmoveTest, OverlapThatDestStartsBeforeSrc) {
+ // Set boundary at beginning and end for not overstepping when
+ // copy forward or backward.
+ unsigned char str[] = {'z', 'a', 'b', 'c', 'z'};
+ const unsigned char expected[] = {'z', 'b', 'c', 'c', 'z'};
+ // dest is &str[1].
+ check_memmove(&str[1], &str[2], 2, str, expected);
+}
+
+TEST_F(MemmoveTest, OverlapThatDestStartsAfterSrc) {
+ unsigned char str[] = {'z', 'a', 'b', 'c', 'z'};
+ const unsigned char expected[] = {'z', 'a', 'a', 'b', 'z'};
+ check_memmove(&str[2], &str[1], 2, str, expected);
+}
+
+// e.g. dest follow src.
+// str: [abcdefghij]
+// [__src_____]
+// [_____dest_]
+TEST_F(MemmoveTest, SrcFollowDest) {
+ unsigned char str[] = {'z', 'a', 'b', 'z'};
+ const unsigned char expected[] = {'z', 'b', 'b', 'z'};
+ check_memmove(&str[1], &str[2], 1, str, expected);
+}
+
+TEST_F(MemmoveTest, DestFollowSrc) {
+ unsigned char str[] = {'z', 'a', 'b', 'z'};
+ const unsigned char expected[] = {'z', 'a', 'a', 'z'};
+ check_memmove(&str[2], &str[1], 1, str, expected);
+}
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