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Should the shift amount be an immediate value, or a value stored in a register? Does both work?

I've had different websites tell me different things and am confused.

Based on my research the sll (shift left logical) instruction should be used like this:

  sll $d, $t, h

Which makes $d = $t shifted left h times.

I've been told that h should be a immediate value, but I was wondering if a register could be used as the third argument, and the value inside that register used as the shift amount. Would that also work?

The Impossible Squish
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2 Answers2

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You are correct.

sll is specific in that it is a R-format instruction where only two registers are used, rd and rs (destination and source), and the shamt field is a immediate value (a constant).

There is another instruction sllv which uses a third register where you specify shift by variable (the register).

dimm
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    Note: `sslv` is a MIPS32r2 instruction. The MIPS32r2 version of the MIPS architecture was introduced in 2002, so it is not yet supported by common educational tools like SPIM and MARS. – markgz Oct 23 '15 at 18:21
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Let me clear the point Shift left logical in MIPS 32 bit has following syntax:

SLL destination, Target, Shift amount(Should be immediate value)

Where as in 8086 if we want shift amount more than 1 we have to use a register to store the value of shift amount!

Nauman Rehmat
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