LLL Leet Code Example

LLL_LeetCode.c

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
__attribute__ ((naked)) int* twoSum(int* nums, 
                                    int numsSize, 
                                    int target, 
                                    int* returnSize)
{
    /* Inline assembly version - using AT&T syntax... */
    __asm__(".intel_syntax noprefix;\
        push rbx;\
        sub rsp, 0x40;\
        ;\
        /* Store our params on the stack... */;\
        /* Note - int's are dword & int* are qword. */;\
        /* rsp + 0x10 <- nums* */;\
        /* rsp + 0x18 <- numsSize */;\
        /* rsp + 0x20 <- target */;\
        /* rsp + 0x28 <- returnSize */;\
        /* rsp + 0x30 <- 'output indicies' */;\
        mov qword ptr[rsp + 0x10], rdi;\
        mov dword ptr[rsp + 0x18], esi;\
        mov dword ptr[rsp + 0x20], edx;\
        mov qword ptr[rsp + 0x28], rcx;\
        ;\
        /* malloc memory... */;\
        mov rdi, 0x08;\
        call malloc;\
        ;\
        /* store ptr to malloc-ed memory */;\
        mov qword ptr[rsp + 0x30], rax;\
        /* outer-loop - iterate over the nums */;\
        xor r8, r8;\
        outerloop%=:\
        ;\
        /* inner-loop - iterate over the other nums */;\
        mov r9, r8;\
        add r9, 0x01;\
        innerloop%=:\
        ;\
        /* Set rbx to point to the first pointer in nums */;\
        mov rbx, qword ptr [rsp + 0x10];\
        xor rax, rax;\
        ;\
        /* Set rbx to point to r8th value of nums... */;\
        /* ...and add value to rax. */;\
        lea rbx, [rbx + r8 * 4];\
        add eax, dword ptr [rbx];\
        ;\
        /* Do the same for the r9th value... */;\
        /* ...remembering to reload rbx. */;\
        mov rbx, qword ptr [rsp + 0x10];\
        lea rbx, [rbx + r9 * 4];\
        add eax, dword ptr [rbx];\
        /* Load target for comparison... */;\
        mov ebx, dword ptr[rsp + 0x20];\
        cmp ebx, eax;\
        ;\
        /* If not equal – continue the loop */;\
        jne continue%=;\
        ;\
        /* Otherwise prepare for returning the answers */;\
        /* Set rax to point to the output memory & copy */;\
        /*   the lower half of r8 (r8d) to the first byte ... */;\
        /*   ...and r9d to the second byte. */;\
        mov rax, qword ptr [rsp + 0x30];\
        mov dword ptr [rax], r8d;\
        lea rax, [rax + 4];\
        mov dword ptr [rax], r9d;\
        ;\
        /* Put a 2 into returnSize... */;\
        mov rax, qword ptr [rsp + 0x28];\
        mov dword ptr [rax], 0x02;\
        jmp leave%=;\
        continue%=:\
        ;\
        /* Increment & check the loop counters */;\
        inc r9;\
        cmp r9d, dword ptr[rsp + 0x18];\
        jle innerloop%=;\
        inc r8;\
        cmp r8d, dword ptr[rsp + 0x18];\
        jle outerloop%=;\
        ;\
        /* Return the answers, via rax */;\
        leave%=:\
        mov rax, qword ptr [rsp + 0x30];\
        add rsp, 0x40;\
        pop rbx;\
        ret;\
        .att_syntax;" : :);
}