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CS485G Spring 2015 18

5. The test instruction (testl b, a) also sets the ﬂags; it’s like com-

puting a&b without modifying the destination. Usually, one of the

two operands is a mask.

(a) sets ZF if a ∧ b = 0

(b) sets SF if a ∧ b < 0

6. Many instructions in the setXX dest family test the condition codes

and set the destination (a single byte) to 0 or 1 based on the result.

sete ZF Equal/Zero

setne ¬ZF Not Equal / Not Zero

sets SF Negative

setns ¬SF Nonnegative

setg ¬(SF⊕OF)∧¬ZF Greater (Signed)

setge ¬(SF⊕OF) Greater or Equal (Signed)

setl (SF⊕OF) Less (Signed)

setle (SF⊕OF)∨ZF Less or Equal (Signed)

seta ¬CF∧¬ZF Above (unsigned)

setb CF Below (unsigned)

7. Many instructions in the jXX dest family jump depending on the con-

dition codes.

jmp true Unconditional

je ZF Equal/Zero

jne ¬ZF Not Equal / Not Zero

js SF Negative

jns ¬SF Nonnegative

jg ¬(SF⊕OF)∧¬ZF Greater (Signed)

jge ¬(SF⊕OF) Greater or Equal (Signed)

jl (SF⊕OF) Less (Signed)

jle (SF⊕OF)∨ZF Less or Equal (Signed)

ja ¬CF∧¬ZF Above (unsigned)

jb CF Below (unsigned)

8. Lecture 11, 2/9/2015

9. Example

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Cirrus Logic CS485 Manual do Utilizador Página 18