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nuttx/libs/libc/libc.h
Justin Hammond afc42d0aa2 libs/libc/string: Copy and compare by words when pointers agree on alignment. 
The BSD string functions take a word path only when both pointers are
aligned, and a byte path otherwise.  A pair at the same offset from a
boundary takes the byte path even though copying or comparing a few leading
bytes aligns both at once, since aligning one aligns the other.

Add MISALIGNED(), which asks whether two pointers disagree about where a
boundary falls, and walk an agreeing pair up to the boundary before the
existing path selection.  MISALIGNED4() does the same for the 4-byte path,
so a pair that is 4-byte but not 8-byte aligned reaches the wide path
instead of the middle one.  No existing line changes: the walk is a new step
ahead of the current decisions.  A pair at differing offsets still takes the
byte path, since no single boundary serves both.

Measured on an EIC7700 EVB (EIC7700X, RV64GC, 1.4GHz) with the BSD string
functions selected and the RISC-V assembly ones disabled, using the
benchmark in apps#3706, medians of 3 runs in MB/s at its largest size:

                equal offset            aligned
  memcpy     414 -> 4148  10.0x    4214 -> 4208
  memcmp      41 ->  361   8.8x     362 ->  360
  strncmp     28 ->  202   7.4x     207 ->  207
  strcmp      42 ->  273   6.5x     278 ->  276
  strncpy    377 -> 1676   4.5x    1824 -> 1748
  stpncpy    376 -> 1654   4.4x    1843 -> 1724
  stpcpy     551 -> 1833   3.3x    1970 -> 1939
  memccpy    650 -> 2012   3.1x    2478 -> 2016
  strcpy     636 -> 1837   2.9x    1678 -> 1965

Cases the walk never runs for move in both directions by up to a third, the
largest being memccpy at differing offsets, 648 -> 414.  Their code is
unchanged, so that is code placement rather than an effect of the change.

The change is architecture independent but has only been measured on
RV64GC.  Word size, alignment cost and byte loop codegen all differ
elsewhere, so the balance wants measuring on other architectures.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
2026-08-24 12:02:02 +08:00

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/****************************************************************************
* libs/libc/libc.h
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
#ifndef __LIBS_LIBC_LIBC_H
#define __LIBS_LIBC_LIBC_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#ifndef __ASSEMBLY__
# include <sys/types.h>
# include <stdbool.h>
# include <stdio.h>
# include <stdlib.h>
# include <limits.h>
# include <semaphore.h>
# include <nuttx/lib/lib.h>
# include <nuttx/streams.h>
#endif
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* This configuration directory is used in environment variable processing
* when we need to reference the user's home directory. There are no user
* directories in NuttX so, by default, this always refers to the root
* directory.
*/
#ifndef CONFIG_LIBC_HOMEDIR
# define CONFIG_LIBC_HOMEDIR "/"
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_MEMCHR_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_MEMCHR_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_MEMCHR
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_MEMCMP_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_MEMCMP_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_MEMCMP
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_MEMCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_MEMCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_MEMCPY
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_MEMMOVE_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_MEMMOVE_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_MEMMOVE
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_MEMSET_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_MEMSET_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_MEMSET
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCAT_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCAT_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCAT
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCASECMP_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCASECMP_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCASECMP
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCHR_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCHR_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCHR
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCHRNUL_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCHRNUL_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCHRNUL
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCMP_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCMP_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCMP
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRCPY
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRLCAT_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRLCAT_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRLCAT
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRLEN_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRLEN_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRLEN
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRLCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRLCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRLCPY
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRNCASECMP_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRNCASECMP_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRNCASECMP
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRNCAT_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRNCAT_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRNCAT
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRNLEN_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRNLEN_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRNLEN
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRNCMP_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRNCMP_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRNCMP
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRNCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRNCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRNCPY
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STRRCHR_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STRRCHR_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STRRCHR
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STPCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STPCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STPCPY
#endif
#if ((!defined(CONFIG_LIBC_PREVENT_STPNCPY_USER) && !defined(__KERNEL__)) || \
(!defined(CONFIG_LIBC_PREVENT_STPNCPY_KERNEL) && defined(__KERNEL__)))
# define LIBC_BUILD_STPNCPY
#endif
#ifdef CONFIG_MM_KASAN
# define ARCH_LIBCFUN(x) arch_##x
#else
# define ARCH_LIBCFUN(x) x
#endif
/* Nonzero if either x or y is not aligned on a "libc_data_t" boundary. */
#define UNALIGNED_X(x) \
(((libc_data_t)(uintptr_t)(x) & (sizeof(libc_data_t) - 1)) != 0)
#define UNALIGNED(x, y) ((UNALIGNED_X(x)) | (UNALIGNED_X(y)))
/* Nonzero if x and y disagree about where a "libc_data_t" boundary falls.
* A pair that agrees can be walked up to the boundary a byte at a time and
* handled a word at a time from there, since aligning one aligns the
* other. A pair that disagrees cannot, because no single boundary serves
* both.
*/
#define MISALIGNED(x, y) \
((((uintptr_t)(x)) ^ ((uintptr_t)(y))) & (sizeof(libc_data_t) - 1))
#define ALIGNED(x) \
(((libc_data_t)(uintptr_t)(x) & (sizeof(libc_data_t) - 1)) == 0)
/* How many bytes are copied each iteration of the word copy loop. */
#define LITTLEBLOCKSIZE (sizeof(libc_data_t))
#define BIGBLOCKSIZE (sizeof(libc_data_t) << 2)
/* Threshold for punting to the byte copier. */
#define TOO_SMALL(len) ((len) < LITTLEBLOCKSIZE)
/* Macros for detecting endchar */
#define DETECTNULL(x) \
(((x) - 0x0101010101010101LL) & ~(x) & 0x8080808080808080LL)
#define DETECTCHAR(x, mask) (DETECTNULL((x) ^ (mask)))
/* 32-bit helpers for the 4-byte middle path on 64-bit platforms.
* When libc_data_t is 8 bytes, pointers that are 4-byte aligned
* but not 8-byte aligned would otherwise fall back to byte-at-a-time.
*/
#define DETECTNULL32(x) \
(((x) - (uint32_t)0x01010101) & ~(x) & (uint32_t)0x80808080)
#define DETECTCHAR32(x, mask) (DETECTNULL32((x) ^ (mask)))
#define UNALIGNED4(x, y) \
((((uintptr_t)(x)) | ((uintptr_t)(y))) & 3)
#define UNALIGNED4_X(x) (((uintptr_t)(x)) & 3)
#define LITTLEBLOCKSIZE4 (sizeof(uint32_t))
#define BIGBLOCKSIZE4 (sizeof(uint32_t) << 2)
#define TOO_SMALL4(len) ((len) < LITTLEBLOCKSIZE4)
#ifndef __ASSEMBLY__
/****************************************************************************
* Public Types
****************************************************************************/
typedef unsigned long long libc_data_t;
/****************************************************************************
* Public Data
****************************************************************************/
#undef EXTERN
#if defined(__cplusplus)
#define EXTERN extern "C"
extern "C"
{
#else
#define EXTERN extern
#endif
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
/* Defined in lib_getfullpath.c */
int lib_getfullpath(int dirfd, FAR const char *path,
FAR char *fullpath, size_t fulllen);
/* Defined in lib_fopen.c */
int lib_mode2oflags(FAR const char *mode);
/* Defined in lib_libfwrite.c */
ssize_t lib_fwrite(FAR const void *ptr, size_t count, FAR FILE *stream);
ssize_t lib_fwrite_unlocked(FAR const void *ptr, size_t count,
FAR FILE *stream);
/* Defined in lib_libfread_unlocked.c */
ssize_t lib_fread_unlocked(FAR void *ptr, size_t count, FAR FILE *stream);
/* Defined in lib_libgets.c */
FAR char *lib_dgets(FAR char *buf, size_t buflen, int fd,
bool keepnl, bool consume);
/* Defined in lib_libfgets.c */
FAR char *lib_fgets(FAR char *buf, size_t buflen, FILE *stream,
bool keepnl, bool consume);
FAR char *lib_fgets_unlocked(FAR char *buf, size_t buflen, FILE *stream,
bool keepnl, bool consume);
/* Defined in lib_flushall.c */
#ifdef CONFIG_FILE_STREAM
int lib_flushall(FAR struct streamlist *list);
int lib_flushall_unlocked(FAR struct streamlist *list);
#endif
/* Defined in lib_libfflush.c */
ssize_t lib_fflush(FAR FILE *stream);
ssize_t lib_fflush_unlocked(FAR FILE *stream);
/* Defined in lib_rdflush_unlocked.c */
int lib_rdflush_unlocked(FAR FILE *stream);
/* Defined in lib_wrflush_unlocked.c */
int lib_wrflush_unlocked(FAR FILE *stream);
/* Defined in lib_libgetbase.c */
int lib_getbase(FAR const char *nptr, FAR const char **endptr);
/* Defined in lib_skipspace.c */
void lib_skipspace(FAR const char **pptr);
/* Defined in lib_isbasedigit.c */
bool lib_isbasedigit(int ch, int base, FAR int *value);
/* Defined in lib_checkbase.c */
int lib_checkbase(int base, FAR const char **pptr);
/* Defined in lib_parsehostfile.c */
#ifdef CONFIG_NETDB_HOSTFILE
struct hostent;
ssize_t lib_parse_hostfile(FAR FILE *stream, FAR struct hostent *host,
FAR char *buf, size_t buflen);
#endif
#ifndef CONFIG_DISABLE_ENVIRON
int lib_restoredir(void);
#endif
/* Defined in lib_cxx_initialize.c */
void lib_cxx_initialize(void);
#undef EXTERN
#if defined(__cplusplus)
}
#endif
#endif /* __ASSEMBLY__ */
#endif /* __LIBS_LIBC_LIBC_H */
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