libc: minimal: add size optimized string functions

The current implementations of memcpy and memset are optimized for
performance and use a word based loop before the byte based loop.

Add a config option that skips the word based loop. This saves 120
bytes on the Cortex-M0+ which is worthwhile on small apps like a
bootloader.

Enable by default if SIZE_OPTIMIZATIONS is set.

Signed-off-by: Michael Hope <mlhx@google.com>
This commit is contained in:
Michael Hope 2021-06-25 20:17:36 +02:00 committed by Anas Nashif
commit 5d55730cf6
2 changed files with 12 additions and 0 deletions

View file

@ -138,6 +138,13 @@ config MINIMAL_LIBC_LL_PRINTF
Build with long long printf enabled. This will increase the size of
the image.
config MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE
bool "Use size optimized string functions"
default y if SIZE_OPTIMIZATIONS
help
Enable smaller but potentially slower implementations of memcpy and
memset. On the Cortex-M0+ this reduces the total code size by 120 bytes.
endif # MINIMAL_LIBC
config STDOUT_CONSOLE

View file

@ -301,6 +301,8 @@ void *memcpy(void *_MLIBC_RESTRICT d, const void *_MLIBC_RESTRICT s, size_t n)
unsigned char *d_byte = (unsigned char *)d;
const unsigned char *s_byte = (const unsigned char *)s;
#if !defined(CONFIG_MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE)
const uintptr_t mask = sizeof(mem_word_t) - 1;
if ((((uintptr_t)d ^ (uintptr_t)s_byte) & mask) == 0) {
@ -328,6 +330,7 @@ void *memcpy(void *_MLIBC_RESTRICT d, const void *_MLIBC_RESTRICT s, size_t n)
d_byte = (unsigned char *)d_word;
s_byte = (unsigned char *)s_word;
}
#endif
/* do byte-sized copying until finished */
@ -353,6 +356,7 @@ void *memset(void *buf, int c, size_t n)
unsigned char *d_byte = (unsigned char *)buf;
unsigned char c_byte = (unsigned char)c;
#if !defined(CONFIG_MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE)
while (((uintptr_t)d_byte) & (sizeof(mem_word_t) - 1)) {
if (n == 0) {
return buf;
@ -380,6 +384,7 @@ void *memset(void *buf, int c, size_t n)
/* do byte-sized initialization until finished */
d_byte = (unsigned char *)d_word;
#endif
while (n > 0) {
*(d_byte++) = c_byte;