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assemblynasmx86-64yasm

What does `000000q` mean?

I am studying x86_64 assembler (yasm) with this textbook. There I have met the following lines that define file access flags:

O_RDONLY        equ    000000q
O_WRONLY        equ    000001q
O_RDWR          equ    000002q

The question is what do their values mean? What q stands for?

Solution

  • In NASM/YASM it is a suffix that means the number is in Octal. From the documentation

    3.5.1. Numeric Constants

    A numeric constant is simply a number. NASM allows you to specify numbers in a variety of number bases, in a variety of ways: you can suffix H, Q or O, and B for hex, octal, and binary, or you can prefix 0x for hex in the style of C, or you can prefix $ for hex in the style of Borland Pascal. Note, though, that the $ prefix does double duty as a prefix on identifiers (see Section 3.1), so a hex number prefixed with a $ sign must have a digit after the $ rather than a letter.

    Some examples:

    mov ax,100              ; decimal
mov ax,0a2h             ; hex
mov ax,$0a2             ; hex again: the 0 is required
mov ax,0xa2             ; hex yet again
mov ax,777q             ; octal
mov ax,777o             ; octal again
mov ax,10010011b        ; binary