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* [glibc] string: Improve generic stpcpy
@ 2023-02-06 20:13 Adhemerval Zanella
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From: Adhemerval Zanella @ 2023-02-06 20:13 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=30c1dfde313fa01e195e0759915f1356effdb7d6
commit 30c1dfde313fa01e195e0759915f1356effdb7d6
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue Jan 31 15:46:08 2023 -0300
string: Improve generic stpcpy
It follows the strategy:
- Align the destination on word boundary using byte operations.
- If source is also word aligned, read a word per time, check for
null (using has_zero from string-fzb.h), and write the remaining
bytes.
- If source is not word aligned, loop by aligning the source, and
merging the result of two reads. Similar to aligned case,
check for null with has_zero, and write the remaining bytes if
null is found.
Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu,
and powerpc-linux-gnu by removing the arch-specific assembly
implementation and disabling multi-arch (it covers both LE and BE
for 64 and 32 bits).
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
Diff:
---
string/stpcpy.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 86 insertions(+), 6 deletions(-)
diff --git a/string/stpcpy.c b/string/stpcpy.c
index 8df5065cfe..dd0fef12ef 100644
--- a/string/stpcpy.c
+++ b/string/stpcpy.c
@@ -15,12 +15,12 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
#define NO_MEMPCPY_STPCPY_REDIRECT
#include <string.h>
+#include <stdint.h>
+#include <memcopy.h>
+#include <string-fzb.h>
+#include <string-misc.h>
#undef __stpcpy
#undef stpcpy
@@ -29,12 +29,92 @@
# define STPCPY __stpcpy
#endif
+static __always_inline char *
+write_byte_from_word (op_t *dest, op_t word)
+{
+ char *d = (char *) dest;
+ for (size_t i = 0; i < OPSIZ; i++, ++d)
+ {
+ char c = extractbyte (word, i);
+ *d = c;
+ if (c == '\0')
+ break;
+ }
+ return d;
+}
+
+static __always_inline char *
+stpcpy_aligned_loop (op_t *restrict dst, const op_t *restrict src)
+{
+ op_t word;
+ while (1)
+ {
+ word = *src++;
+ if (has_zero (word))
+ break;
+ *dst++ = word;
+ }
+
+ return write_byte_from_word (dst, word);
+}
+
+static __always_inline char *
+stpcpy_unaligned_loop (op_t *restrict dst, const op_t *restrict src,
+ uintptr_t ofs)
+{
+ op_t w2a = *src++;
+ uintptr_t sh_1 = ofs * CHAR_BIT;
+ uintptr_t sh_2 = OPSIZ * CHAR_BIT - sh_1;
+
+ op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2);
+ if (!has_zero (w2))
+ {
+ op_t w2b;
+
+ /* Unaligned loop. The invariant is that W2B, which is "ahead" of W1,
+ does not contain end-of-string. Therefore it is safe (and necessary)
+ to read another word from each while we do not have a difference. */
+ while (1)
+ {
+ w2b = *src++;
+ w2 = MERGE (w2a, sh_1, w2b, sh_2);
+ /* Check if there is zero on w2a. */
+ if (has_zero (w2))
+ goto out;
+ *dst++ = w2;
+ if (has_zero (w2b))
+ break;
+ w2a = w2b;
+ }
+
+ /* Align the final partial of P2. */
+ w2 = MERGE (w2b, sh_1, 0, sh_2);
+ }
+
+out:
+ return write_byte_from_word (dst, w2);
+}
+
+
/* Copy SRC to DEST, returning the address of the terminating '\0' in DEST. */
char *
STPCPY (char *dest, const char *src)
{
- size_t len = strlen (src);
- return memcpy (dest, src, len + 1) + len;
+ /* Copy just a few bytes to make DEST aligned. */
+ size_t len = (-(uintptr_t) dest) % OPSIZ;
+ for (; len != 0; len--, ++dest)
+ {
+ char c = *src++;
+ *dest = c;
+ if (c == '\0')
+ return dest;
+ }
+
+ /* DEST is now aligned to op_t, SRC may or may not be. */
+ uintptr_t ofs = (uintptr_t) src % OPSIZ;
+ return ofs == 0 ? stpcpy_aligned_loop ((op_t*) dest, (const op_t *) src)
+ : stpcpy_unaligned_loop ((op_t*) dest,
+ (const op_t *) (src - ofs) , ofs);
}
weak_alias (__stpcpy, stpcpy)
libc_hidden_def (__stpcpy)
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