github.com/afumu/libc@v0.0.6/musl/src/string/memcpy.c (about)

     1  #include <string.h>
     2  #include <stdint.h>
     3  #include <endian.h>
     4  
     5  void *memcpy(void *restrict dest, const void *restrict src, size_t n)
     6  {
     7  	unsigned char *d = dest;
     8  	const unsigned char *s = src;
     9  
    10  #ifdef __GNUC__
    11  
    12  #if __BYTE_ORDER == __LITTLE_ENDIAN
    13  #define LS >>
    14  #define RS <<
    15  #else
    16  #define LS <<
    17  #define RS >>
    18  #endif
    19  
    20  	typedef uint32_t __attribute__((__may_alias__)) u32;
    21  	uint32_t w, x;
    22  
    23  	for (; (uintptr_t)s % 4 && n; n--) *d++ = *s++;
    24  
    25  	if ((uintptr_t)d % 4 == 0) {
    26  		for (; n>=16; s+=16, d+=16, n-=16) {
    27  			*(u32 *)(d+0) = *(u32 *)(s+0);
    28  			*(u32 *)(d+4) = *(u32 *)(s+4);
    29  			*(u32 *)(d+8) = *(u32 *)(s+8);
    30  			*(u32 *)(d+12) = *(u32 *)(s+12);
    31  		}
    32  		if (n&8) {
    33  			*(u32 *)(d+0) = *(u32 *)(s+0);
    34  			*(u32 *)(d+4) = *(u32 *)(s+4);
    35  			d += 8; s += 8;
    36  		}
    37  		if (n&4) {
    38  			*(u32 *)(d+0) = *(u32 *)(s+0);
    39  			d += 4; s += 4;
    40  		}
    41  		if (n&2) {
    42  			*d++ = *s++; *d++ = *s++;
    43  		}
    44  		if (n&1) {
    45  			*d = *s;
    46  		}
    47  		return dest;
    48  	}
    49  
    50  	if (n >= 32) switch ((uintptr_t)d % 4) {
    51  	case 1:
    52  		w = *(u32 *)s;
    53  		*d++ = *s++;
    54  		*d++ = *s++;
    55  		*d++ = *s++;
    56  		n -= 3;
    57  		for (; n>=17; s+=16, d+=16, n-=16) {
    58  			x = *(u32 *)(s+1);
    59  			*(u32 *)(d+0) = (w LS 24) | (x RS 8);
    60  			w = *(u32 *)(s+5);
    61  			*(u32 *)(d+4) = (x LS 24) | (w RS 8);
    62  			x = *(u32 *)(s+9);
    63  			*(u32 *)(d+8) = (w LS 24) | (x RS 8);
    64  			w = *(u32 *)(s+13);
    65  			*(u32 *)(d+12) = (x LS 24) | (w RS 8);
    66  		}
    67  		break;
    68  	case 2:
    69  		w = *(u32 *)s;
    70  		*d++ = *s++;
    71  		*d++ = *s++;
    72  		n -= 2;
    73  		for (; n>=18; s+=16, d+=16, n-=16) {
    74  			x = *(u32 *)(s+2);
    75  			*(u32 *)(d+0) = (w LS 16) | (x RS 16);
    76  			w = *(u32 *)(s+6);
    77  			*(u32 *)(d+4) = (x LS 16) | (w RS 16);
    78  			x = *(u32 *)(s+10);
    79  			*(u32 *)(d+8) = (w LS 16) | (x RS 16);
    80  			w = *(u32 *)(s+14);
    81  			*(u32 *)(d+12) = (x LS 16) | (w RS 16);
    82  		}
    83  		break;
    84  	case 3:
    85  		w = *(u32 *)s;
    86  		*d++ = *s++;
    87  		n -= 1;
    88  		for (; n>=19; s+=16, d+=16, n-=16) {
    89  			x = *(u32 *)(s+3);
    90  			*(u32 *)(d+0) = (w LS 8) | (x RS 24);
    91  			w = *(u32 *)(s+7);
    92  			*(u32 *)(d+4) = (x LS 8) | (w RS 24);
    93  			x = *(u32 *)(s+11);
    94  			*(u32 *)(d+8) = (w LS 8) | (x RS 24);
    95  			w = *(u32 *)(s+15);
    96  			*(u32 *)(d+12) = (x LS 8) | (w RS 24);
    97  		}
    98  		break;
    99  	}
   100  	if (n&16) {
   101  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   102  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   103  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   104  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   105  	}
   106  	if (n&8) {
   107  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   108  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   109  	}
   110  	if (n&4) {
   111  		*d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
   112  	}
   113  	if (n&2) {
   114  		*d++ = *s++; *d++ = *s++;
   115  	}
   116  	if (n&1) {
   117  		*d = *s;
   118  	}
   119  	return dest;
   120  #endif
   121  
   122  	for (; n; n--) *d++ = *s++;
   123  	return dest;
   124  }