A PowerPC instruction a day series: 0

Plan:
Here are some PowerPC instructions that are useful to beginners:

li REG, VALUE

    loads register REG with the number VALUE
add REGA, REGB, REGC

    adds REGB with REGC and stores the result in REGA
addi REGA, REGB, VALUE

    add the number VALUE to REGB and stores the result in REGA
mr REGA, REGB

    copies the value in REGB into REGA
or REGA, REGB, REGC

    performs a logical "or" between REGB and REGC, and stores the result in REGA
ori REGA, REGB, VALUE

    performs a logical "or" between REGB and VALUE, and stores the result in REGA
and, andi, xor, xori, nand, nand, and nor

    all of these follow the same pattern as "or" and "ori" for the other logical operations
ld REGA, 0(REGB)

    use the contents of REGB as the memory address of the value to load into REGA
lbz, lhz, and lwz

    all of these follow the same format, but operate on bytes, halfwords, and words, respectively (the "z" indicates that they also zero-out the rest of the register)
b ADDRESS

    jump (or branch) to the instruction at address ADDRESS
bl ADDRESS

    subroutine call to address ADDRESS
cmpd REGA, REGB

    compare the contents of REGA and REGB, and set the bits of the status register appropriately
beq ADDRESS

    branch to ADDRESS if the previously compared register contents were equal
bne, blt, bgt, ble, and bge

    all of these follow the same form, but check for inequality, less than, greater than, less than or equal to, and greater than or equal to, respectively.
std REGA, 0(REGB)

    use the contents of REGB as the memory address to save the value of REGA into
stb, sth, and stw

    all of these follow the same format, but operate on bytes, halfwords, and words, respectively
sc

    makes a system call to the kernel