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MIPS instructions

MIPS instructions. MIPS Assembly for if-then-else. Now it is straightforward to translate the C program into MIPS assembly Problem is how do you implement this jump. How to Encode Branch Instructions.

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MIPS instructions

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  1. MIPS instructions week04-3.ppt

  2. MIPS Assembly for if-then-else • Now it is straightforward to translate the C program into MIPS assembly • Problem is how do you implement this jump week04-3.ppt

  3. How to Encode Branch Instructions • To encode these branch instructions, we first need to figure out the value for the associated label • This will be done by the assembler • Note that the MIPS has the alignment restriction, which means all the labels will be a multiple of 4 • To increase the range, the address divided by 4 is actually encoded • In other words, the address is in terms of words (32 bits), rather than bytes week04-3.ppt

  4. Encoding Conditional Branch Instructions • It branches the number of the instructions specified by the offset if register rs equals to register rt • In the stored-program concept, we implicitly need a register to hold the address of the current instruction being executed • Which is called program counter (PC) (should be called instruction address register) • What is the value of PC after we finish executing the current instruction? week04-3.ppt

  5. Abstract View of MIPS Implementation week04-3.ppt

  6. Encoding Conditional Branch Instructions • PC-relative addressing • The offset of conditional branch instructions is relative to PC + 4 • Since all MIPS instructions are 4 bytes long, the offset refers to the number of words to the next instruction instead of the number of bytes week04-3.ppt

  7. Example • What is the encoding of • In other words, what should be the offset? week04-3.ppt

  8. Encoding bne 31 26 25 21 20 16 15 0 opcode rs rt Immediate Value rs Label/Offset bne $19, $20, Else rt 31 26 25 21 20 16 15 0 0 0 0 1 0 1 1 0 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 opcode rs rt Immediate Value 0 0 0 1 0 1 1 0 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 Encoding = 0x16740002 week04-3.ppt

  9. Compiling a while loop in C • How to translate the following to MIPS assembly? • We first translate into a C program using if and goto week04-3.ppt

  10. Compiling a while loop in C • Assume that i and k correspond to registers $s3 and $s5 and base array save is in $s6 week04-3.ppt

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