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authorRich Felker <dalias@aerifal.cx>2013-08-28 03:34:57 -0400
committerRich Felker <dalias@aerifal.cx>2013-08-28 03:34:57 -0400
commit90edf1cc15cec685c18ec2485ddce5b655963464 (patch)
tree97b728abcd94fbb0e41a2a1d14a7a15d70b24c36 /src/string
parent38e6acbf89afd3dfabb4f4d0506319c339b13663 (diff)
downloadmusl-90edf1cc15cec685c18ec2485ddce5b655963464.tar.gz
optimized C memcpy
unlike the old C memcpy, this version handles word-at-a-time reads and writes even for misaligned copies. it does not require that the cpu support misaligned accesses; instead, it performs bit shifts to realign the bytes for the destination. essentially, this is the C version of the ARM assembly language memcpy. the ideas are all the same, and it should perform well on any arch with a decent number of general-purpose registers that has a barrel shift operation. since the barrel shifter is an optional cpu feature on microblaze, it may be desirable to provide an alternate asm implementation on microblaze, but otherwise the C code provides a competitive implementation for "generic risc-y" cpu archs that should alleviate the urgent need for arch-specific memcpy asm.
Diffstat (limited to 'src/string')
-rw-r--r--src/string/memcpy.c127
1 files changed, 111 insertions, 16 deletions
diff --git a/src/string/memcpy.c b/src/string/memcpy.c
index 8e98302f..06e88742 100644
--- a/src/string/memcpy.c
+++ b/src/string/memcpy.c
@@ -1,29 +1,124 @@
#include <string.h>
-#include <stdlib.h>
#include <stdint.h>
-
-#define SS (sizeof(size_t))
-#define ALIGN (sizeof(size_t)-1)
-#define ONES ((size_t)-1/UCHAR_MAX)
+#include <endian.h>
void *memcpy(void *restrict dest, const void *restrict src, size_t n)
{
unsigned char *d = dest;
const unsigned char *s = src;
- if (((uintptr_t)d & ALIGN) != ((uintptr_t)s & ALIGN))
- goto misaligned;
+#ifdef __GNUC__
+
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define LS >>
+#define RS <<
+#else
+#define LS <<
+#define RS >>
+#endif
+
+ typedef uint32_t __attribute__((__may_alias__)) u32;
+ uint32_t w, x;
- for (; ((uintptr_t)d & ALIGN) && n; n--) *d++ = *s++;
- if (n) {
- size_t *wd = (void *)d;
- const size_t *ws = (const void *)s;
+ for (; (uintptr_t)s % 4 && n; n--) *d++ = *s++;
- for (; n>=SS; n-=SS) *wd++ = *ws++;
- d = (void *)wd;
- s = (const void *)ws;
-misaligned:
- for (; n; n--) *d++ = *s++;
+ if ((uintptr_t)d % 4 == 0) {
+ for (; n>=16; s+=16, d+=16, n-=16) {
+ *(u32 *)(d+0) = *(u32 *)(s+0);
+ *(u32 *)(d+4) = *(u32 *)(s+4);
+ *(u32 *)(d+8) = *(u32 *)(s+8);
+ *(u32 *)(d+12) = *(u32 *)(s+12);
+ }
+ if (n&8) {
+ *(u32 *)(d+0) = *(u32 *)(s+0);
+ *(u32 *)(d+4) = *(u32 *)(s+4);
+ d += 8; s += 8;
+ }
+ if (n&4) {
+ *(u32 *)(d+0) = *(u32 *)(s+0);
+ d += 4; s += 4;
+ }
+ if (n&2) {
+ *d++ = *s++; *d++ = *s++;
+ }
+ if (n&1) {
+ *d = *s;
+ }
+ return dest;
+ }
+
+ if (n >= 32) switch ((uintptr_t)d % 4) {
+ case 1:
+ w = *(u32 *)s;
+ *d++ = *s++;
+ *d++ = *s++;
+ *d++ = *s++;
+ n -= 3;
+ for (; n>=17; s+=16, d+=16, n-=16) {
+ x = *(u32 *)(s+1);
+ *(u32 *)(d+0) = (w LS 24) | (x RS 8);
+ w = *(u32 *)(s+5);
+ *(u32 *)(d+4) = (x LS 24) | (w RS 8);
+ x = *(u32 *)(s+9);
+ *(u32 *)(d+8) = (w LS 24) | (x RS 8);
+ w = *(u32 *)(s+13);
+ *(u32 *)(d+12) = (x LS 24) | (w RS 8);
+ }
+ break;
+ case 2:
+ w = *(u32 *)s;
+ *d++ = *s++;
+ *d++ = *s++;
+ n -= 2;
+ for (; n>=18; s+=16, d+=16, n-=16) {
+ x = *(u32 *)(s+2);
+ *(u32 *)(d+0) = (w LS 16) | (x RS 16);
+ w = *(u32 *)(s+6);
+ *(u32 *)(d+4) = (x LS 16) | (w RS 16);
+ x = *(u32 *)(s+10);
+ *(u32 *)(d+8) = (w LS 16) | (x RS 16);
+ w = *(u32 *)(s+14);
+ *(u32 *)(d+12) = (x LS 16) | (w RS 16);
+ }
+ break;
+ case 3:
+ w = *(u32 *)s;
+ *d++ = *s++;
+ n -= 1;
+ for (; n>=19; s+=16, d+=16, n-=16) {
+ x = *(u32 *)(s+3);
+ *(u32 *)(d+0) = (w LS 8) | (x RS 24);
+ w = *(u32 *)(s+7);
+ *(u32 *)(d+4) = (x LS 8) | (w RS 24);
+ x = *(u32 *)(s+11);
+ *(u32 *)(d+8) = (w LS 8) | (x RS 24);
+ w = *(u32 *)(s+15);
+ *(u32 *)(d+12) = (x LS 8) | (w RS 24);
+ }
+ break;
+ }
+ if (n&16) {
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
}
+ if (n&8) {
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ }
+ if (n&4) {
+ *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
+ }
+ if (n&2) {
+ *d++ = *s++; *d++ = *s++;
+ }
+ if (n&1) {
+ *d = *s;
+ }
+ return dest;
+#endif
+
+ for (; n; n--) *d++ = *s++;
return dest;
}