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test instruction

An instruction that ANDs two values only to set the flags, often used to ask "is this zero?" or "is this bit set?".

test a, b (x86-64) and tst xa, xb (ARM64, ands xzr, xa, xb) compute a & b, set ZF/SF (Z/N) from it, clear CF and OF (C and V), and write no register; test eax, eax checks for zero.

Examples

  • test eax, eax then je jumps when eax is 0, without changing eax.

See also

zero flag carry flag sign flag
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