I would appreciate some help with this question.

The 32 bit numbers below represent a MIPS instruction. identify the different fields and state which instruction it is. give the assembler source code that can be converted into this instruction.


I separated the bits and I know the first 6 bits are the opcode and given the opcode it means Addi. The last 16 bits are the immediate value which I have converted to 15. I do need help with the registers and converting the binary into the register number. I have looked everywhere and can not find an explanation. Any help would be appreciated. i know the structure takes this format:

Addi, t,s, 15


You've basically got the answer already: the s register is number 0b10001 = 17, the t register is number 0b10010 = 18.

The instruction is not quite the way you've said it: standard MIPS has the registers in the opposite order, so it's opcode rs rt immediate. The opcode is 0b001000 = 8 = ADDI; rs is 0b10001 = 17 = $s1; rt is 0b10010 = 18 = $s2; the immediate value is 0b0000000000001111 = 15.

(The prefix 0b indicates that the following number is in binary.)

  • $\begingroup$ Thank you. i haven't been able to find an information on it. would i need to write $t17? $\endgroup$ – jessie Aug 31 '18 at 20:24
  • $\begingroup$ @jessie For the registers? For e.g. register 17 you can either use $17 or $s1 (its symbolic name). $\endgroup$ – Draconis Aug 31 '18 at 20:30
  • $\begingroup$ is there an efficient way to convert say r17 to its symbolic name $s1? $\endgroup$ – jessie Aug 31 '18 at 20:32
  • $\begingroup$ @jessie Looking it up in a table is the easiest way. This one was the first hit on Google. $\endgroup$ – Draconis Aug 31 '18 at 20:34
  • $\begingroup$ Thank you. this will help with my studies. can i ask if i was to convert the other way say: add r3, r5, r4. Would you know how i would go about converting those registers? would it be as simple as convert say r4 to 0100? $\endgroup$ – jessie Aug 31 '18 at 20:37

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