Difference between JE JNE and JZ JNZ

Question

In x86 assembly code  are JE and JNE exactly the same as JZ and JNZ

User · Answer

je   Jump if equal     399  3fb    64 48 33 0c 25 28 00    xor     fs 0x28  rcx   400  402    00 00   401  404    74 05                   je     40b  lt sims get counter 0x51 gt

User · Answer

From the Intel s manual - Instruction Set Reference  the JE and JZ have the same opcode  74 for rel8   0F 84 for rel 16 32  also  JNE and JNZ  75 for rel8   0F 85 for rel 16 32  share opcodes   JE and JZ they both check for the ZF  or zero flag   although the manual differs slightly in the descriptions of the first JE rel8 and JZ rel8 ZF usage  but basically they are the same   Here is an extract from the manual s pages 464  465 and 467     Op Code      mnemonic    Description  ----------- ----------- -----------------------------------------------    74 cb        JE rel8     Jump short if equal  ZF 1    74 cb        JZ rel8     Jump short if zero  ZF   1     0F 84 cw     JE rel16    Jump near if equal  ZF 1   Not supported in 64-bit mode   0F 84 cw     JZ rel16    Jump near if 0  ZF 1   Not supported in 64-bit mode    0F 84 cd     JE rel32    Jump near if equal  ZF 1    0F 84 cd     JZ rel32    Jump near if 0  ZF 1     75 cb        JNE rel8    Jump short if not equal  ZF 0    75 cb        JNZ rel8    Jump short if not zero  ZF 0     0F 85 cd     JNE rel32   Jump near if not equal  ZF 0    0F 85 cd     JNZ rel32   Jump near if not zero  ZF 0

User · Answer

JE and JZ are just different names for exactly the same thing  a conditional jump when ZF  the  zero  flag  is equal to 1    Similarly  JNE and JNZ are just different names for a conditional jump when ZF is equal to 0    You could use them interchangeably  but you should use them depending on what you are doing    JZ JNZ are more appropriate when you are explicitly testing for something being equal to zero   dec  ecx jz   counter is now zero  JE and JNE are more appropriate after a CMP instruction   cmp  edx  42 je   the answer is 42    A CMP instruction performs a subtraction  and throws the value of the result away  while keeping the flags  which is why you get ZF 1 when the operands are equal and ZF 0 when they re not

[assembly] Difference between JE/JNE and JZ/JNZ

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