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>
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2 changed files with 12 additions and 0 deletions
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@ -138,6 +138,13 @@ config MINIMAL_LIBC_LL_PRINTF
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Build with long long printf enabled. This will increase the size of
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the image.
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config MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE
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bool "Use size optimized string functions"
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default y if SIZE_OPTIMIZATIONS
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help
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Enable smaller but potentially slower implementations of memcpy and
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memset. On the Cortex-M0+ this reduces the total code size by 120 bytes.
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endif # MINIMAL_LIBC
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config STDOUT_CONSOLE
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@ -301,6 +301,8 @@ void *memcpy(void *_MLIBC_RESTRICT d, const void *_MLIBC_RESTRICT s, size_t n)
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unsigned char *d_byte = (unsigned char *)d;
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const unsigned char *s_byte = (const unsigned char *)s;
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#if !defined(CONFIG_MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE)
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const uintptr_t mask = sizeof(mem_word_t) - 1;
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if ((((uintptr_t)d ^ (uintptr_t)s_byte) & mask) == 0) {
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@ -328,6 +330,7 @@ void *memcpy(void *_MLIBC_RESTRICT d, const void *_MLIBC_RESTRICT s, size_t n)
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d_byte = (unsigned char *)d_word;
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s_byte = (unsigned char *)s_word;
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}
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#endif
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/* do byte-sized copying until finished */
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@ -353,6 +356,7 @@ void *memset(void *buf, int c, size_t n)
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unsigned char *d_byte = (unsigned char *)buf;
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unsigned char c_byte = (unsigned char)c;
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#if !defined(CONFIG_MINIMAL_LIBC_OPTIMIZE_STRING_FOR_SIZE)
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while (((uintptr_t)d_byte) & (sizeof(mem_word_t) - 1)) {
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if (n == 0) {
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return buf;
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@ -380,6 +384,7 @@ void *memset(void *buf, int c, size_t n)
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/* do byte-sized initialization until finished */
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d_byte = (unsigned char *)d_word;
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#endif
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while (n > 0) {
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*(d_byte++) = c_byte;
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