97 lines
1.5 KiB
NASM
97 lines
1.5 KiB
NASM
section .text
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global strlen
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global strcpy
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global strcat
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global strcmp
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;----- strlen(char* str) -----;
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; return value: amount of characters before EOS was found
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strlen:
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push rbp
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mov rbp, rsp
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xor rax, rax
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.findEOS:
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cmp byte [rdi+rax], 0x0
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je .quit
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inc rax
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jmp .findEOS
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.quit:
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leave
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ret
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;----- strcpy(char* dest, char* src) -----;
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; return value: pointer to dest or NULL if nothing was copied (note that EOS is always copied to dest)
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strcpy:
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push rbp
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mov rbp, rsp
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mov r11, rdi
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xor rax, rax
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xor rcx, rcx
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.loop:
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cmp byte [rsi], 0x0
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je .0f
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mov r10b, byte [rsi]
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mov byte [r11], r10b
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inc rsi
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inc r11
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inc rcx
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jmp .loop
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.0f:
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mov byte [r11], 0x0
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cmp rcx, 0
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je .quit
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mov rax, rdi
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.quit:
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leave
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ret
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;----- strcat(char* dest, char* src) -----;
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; return value: pointer to dest
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strcat:
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push rbp
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mov rbp, rsp
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push rdi
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sub rsp, 8
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call strlen
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add rdi, rax
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call strcpy
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add rsp, 8
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pop rax
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leave
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ret
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;----- strcmp(char* str1, char* str2) -----;
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; return value: 0 if both strings are the same, otherwise index in array str1 where strings are to become different
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; returns -1 if str2 is longer than str1 and no difference was found before that happens
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strcmp:
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push rbp
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mov rbp, rsp
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call strlen
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mov rcx, rax
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mov rax, -1
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.compareLoop:
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inc rax
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cmp byte [rdi+rax], 0x0
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je .eosFound
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mov r10b, byte [rsi+rax]
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cmp byte [rdi+rax], r10b
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je .compareLoop
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jmp .quit
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.eosFound:
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mov r10, rax
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mov rdi, rsi
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call strlen
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cmp rax, r10
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jle .quit
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mov rax, -1
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.quit:
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leave
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ret
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