Answer:
A 16-bit two's complement negative one:
FF FF = 1111 1111 1111 1111
Sign-extended:
FF FF FF FF = 1111 1111 1111 1111 1111 1111 1111 1111
The sign-extended version is a 32-bit negative one.
A 16-bit two's complement negative one:
FF FF = 1111 1111 1111 1111
Sign-extended:
FF FF FF FF = 1111 1111 1111 1111 1111 1111 1111 1111
The sign-extended version is a 32-bit negative one.
addiu Instruction
The addiu
instruction
includes a 16-bit immediate operand.
When the ALU executes the instruction,
the immediate operand is sign-extended to 32 bits.
If two's complement overflow occurs during the addition, it is ignored.
addiu d,s,const # $d <—— s + const.
# Const is 16-bit two's comp. sign-extended to 32 bits
# when the addition is done. No overflow trap.
There is also an add immediate instruction that does trap if overflow is detected during addition. We won't use it:
addi d,s,const # $d <—— s + const.
# Const is 16-bit two's comp. sign-extended to 32 bits
# when the addition is done. Overflow trap.
Here is the previous program, that added +146 with -82.
Rewrite it using the addiu instruction.
Put the result in $10.
ori $7, $0, 146 # put +146 into $7
ori $8, $0, 82 # put 82 into $8
nor $8, $8, $0 # reflect
ori $9, $9, 1 #
addu $8, $8, $9 # add 1: $8 = -82
addu $10, $7, $8 # (+146) + (-82)