diff options
| -rw-r--r-- | libc/string/i386/memset.c | 65 |
1 files changed, 56 insertions, 9 deletions
diff --git a/libc/string/i386/memset.c b/libc/string/i386/memset.c index cfc16983c..9f51f3c60 100644 --- a/libc/string/i386/memset.c +++ b/libc/string/i386/memset.c @@ -28,21 +28,68 @@ * More importantly, these should provide a good example for * others to follow when adding arch specific optimizations. * -Erik + * + * 2009-04: modified by Denys Vlasenko <vda.linux@googlemail.com> + * Fill byte-by-byte is a bit too slow. I prefer 46 byte function + * which fills x4 faster than 21 bytes one. */ #include <string.h> -/* Experimentally off - libc_hidden_proto(memset) */ #undef memset void *memset(void *s, int c, size_t count) { - int d0, d1; - __asm__ __volatile__( - "rep\n\t" - "stosb" - : "=&c" (d0), "=&D" (d1) - :"a" (c),"1" (s),"0" (count) - :"memory"); - return s; + int reg, edi; + __asm__ __volatile__( + + /* Most of the time, count is divisible by 4 and nonzero */ + /* It's better to make this case faster */ + /* " jecxz 9f\n" - (optional) count == 0: goto ret */ + " mov %%ecx, %1\n" + " shr $2, %%ecx\n" + " jz 1f\n" /* zero words: goto fill_bytes */ + /* extend 8-bit fill to 32 bits */ + " movzx %%al, %%eax\n" /* 3 bytes */ + /* or: " and $0xff, %%eax\n" - 5 bytes */ + " imul $0x01010101, %%eax\n" /* 6 bytes */ + /* fill full words */ + " rep; stosl\n" + /* fill 0-3 bytes */ + "1: and $3, %1\n" + " jz 9f\n" /* (count & 3) == 0: goto end */ + "2: stosb\n" + " dec %1\n" + " jnz 2b\n" + /* end */ + "9:\n" + + : "=&D" (edi), "=&r" (reg) + : "0" (s), "a" (c), "c" (count) + : "memory" + ); + return s; } libc_hidden_def(memset) + +/* +gcc 4.3.1 +========= +57 push %edi +8b 7c 24 08 mov 0x8(%esp),%edi +8b 4c 24 10 mov 0x10(%esp),%ecx +8b 44 24 0c mov 0xc(%esp),%eax +89 ca mov %ecx,%edx +c1 e9 02 shr $0x2,%ecx +74 0b je 1f <__GI_memset+0x1f> +0f b6 c0 movzbl %al,%eax +69 c0 01 01 01 01 imul $0x1010101,%eax,%eax +f3 ab rep stos %eax,%es:(%edi) +83 e2 03 and $0x3,%edx +74 04 je 28 <__GI_memset+0x28> +aa stos %al,%es:(%edi) +4a dec %edx +75 fc jne 24 <__GI_memset+0x24> +8b 44 24 08 mov 0x8(%esp),%eax +5f pop %edi +c3 ret +*/ |