CODEWITHSUNDEEP
assemblymipsspimpcspim
coool killer
coool killer

Reputation: 23

Spim Instruction division

[0x00400000]    0x3c011000  lui $1, 4096                    ; 5: li $t0, 0x100000F4
[0x00400004]    0x342800f4  ori $8, $1, 244
[0x00400008]    0x8d100000  lw $16, 0($8)                   ; 6: lw $s0, 0($t0)

the above is my spim program, I am curious about the li instruction getting divied into lui and ori could anyone explain what is going on there?

any help appreciated thanks!!

Upvotes: 1

Views: 366

Answers (2)

Variable Length Coder
Variable Length Coder

Reputation: 8116

li is load immediate. However, the value that you're trying to load is too big to fit into the immediate data section of that instruction. The assembler therefore splits it up into two instructions that each load half of that value into the upper and lower parts of that register.

Upvotes: 0

daurnimator
daurnimator

Reputation: 4311

li is a pseudo-instruction (ie, it doesn't exist as an opcode on processors). it is always expanded into a 'load upper immediate'; and an 'or with immediate' instruction:

effectively: (4096 << 16) || 244

The lui instruction will be skipped if the number is not large; and ori will or with the 0 register.

Upvotes: 2

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