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align 4

; @brief Check whether given string lays in userspace memory, i.e. below OS_BASE

; @param base Base address of string

; @return ZF = 1 if string in userspace memory,

;         zf = 0 otherwise

proc is_string_userspace stdcall, base:dword

        push    eax ecx edi

        xor     eax, eax

        mov     edi, [base]

        mov     ecx, OS_BASE-1

        sub     ecx, edi

        jb      .done           ; zf

        inc     ecx

        cmp     ecx, 0x10000    ; don't allow strings larger than 64k?

        jbe     @f

        mov     ecx, 0x10000

@@:

        repnz scasb

.done:

        pop     edi ecx eax

        ret

endp