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7 | 7 | ; int asm_memcpy(void *dest, const void *src, size_t n); |
8 | 8 | ; copies n bytes from memory area src to memory area dest |
9 | 9 | asm_memcpy: |
10 | | - ;;prologue |
11 | | -pushrbp ; Set up stack frame |
12 | | -movrbp,rsp |
13 | | -pushrcx |
14 | | -pushr15 |
15 | | - ;;prologue end |
16 | | - |
17 | | -movr15b,0 ; variable c |
18 | | -movrcx,rdx ; counter i |
19 | | - |
20 | | -;loop_str - while loop |
21 | | -loop_str: |
22 | | -cmp[rdi], byte 0 ; (!dest) |
23 | | -je loopend |
24 | | -movr15b,[rsi] ; c = *src |
25 | | -mov[rdi],r15b ; *dest = c |
26 | | -addrdi,1 ; Increment the first string *dest++; |
27 | | -addrsi,1 ; Increment the second string *src++; |
28 | | -cmprcx,0 ; (count > 0) |
29 | | -jle loopend |
30 | | -cmp[rsi], byte 0 ; (!src) |
31 | | -je loopend |
32 | | -subrcx,1; |
33 | | -jmp loop_str |
34 | | -loopend: |
35 | | - ;;epilogue |
36 | | -popr15 |
37 | | -poprcx |
38 | | -movrsp,rbp ; Restore previous stack frame |
39 | | -poprbp |
40 | | - ;;epilogue end |
41 | | -ret ; Return from procedure |
| 10 | +movrax,rdi ; Copy the pointer to @dest string to be returned |
| 11 | +movecx,edx ; Copy the length @n to the counter |
| 12 | +cld ; Clear the direction flag, DL |
| 13 | +repmovsb ; Copy @n bytes from ESI (source) to EDI (destination) |
| 14 | +ret ; Return |
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