qword2string.asm

; const char *, qword STRING.FROM_QWORD(char RDI buffer[RSI], qword RSI, signed qword RDX value)
export_function STRING.FROM_QWORD:
    ;qword R8 len = 0;
    MOV     R8, 0
    ;bool R9 negative = false;
    MOV     R9, FALSE

    ;if (value < 0)
    CMP     RDX, 0
    JGE     .0_l
    ;negative = true
    MOV     R9, TRUE
    ;value = -value
    NEG     RDX

    ;do
    .0_l:
        ;R9 = value //save value, RDX is used for the remainder
        ;RAX = value / 10, RDX = value % 10
        MOV     RAX, RDX
        MOV     RDX, 0
        MOV     RCX, 10
        DIV     RCX

        MOV     R10, RAX
        MOV     RAX, RDX
        MOV     RDX, R9

        ;buffer[len] = RAX + '0'
        MOV     [RDI + R8], AL
        ADD     [RDI + R8], BYTE '0'

        ;len++
        INC     R8

        ;value = R10 (R10 is the result of the division)
        MOV     RDX, R10

        ;while (value != 0)
        CMP     RDX, 0
        JNE     .0_l

    ;if (negative)
    CMP    R9, TRUE
    JNE    .1_l
        ;buffer[len] = '-'
        MOV     [RDI + R8], BYTE '-'
        ;len++
        INC     R8
    .1_l:
    ;buffer[len] = 0x0
    MOV     [RDI + R8], BYTE 0x0

    ; Reverse the string
    ;qword R10 i = 0;
    MOV     R10, 0
    ;for (i; i < len / 2; i++)
    .2_l:
        CMP     R10, R8
        JAE     .3_l
        ;char R11 tmp = buffer[i];
        MOV     R11, [RDI + R10]
        ; char *R12 = buffer + len - i - 1;
        MOV     R12, RDI
        ADD     R12, R8
        SUB     R12, R10
        DEC     R12
        ;buffer[i] = buffer[len - i - 1];
        MOV     AL, [R12]
        MOV     [RDI + R10], AL
        ;buffer[len - i - 1] = tmp;
        MOV     [R12], R11
        ;i++
        INC     R10
        JMP     .2_l

    .3_l:

    ;return buffer, len
    MOV     RAX, RDI
    MOV     RDX, R8
end