strb w0,[r1,0] // like str but writes one byte only - note the use of w0 instead of r0 for the source register name

stur r0,[r1,0] // store register r0 to the address pointed to by (r1 + 0) - the mnemonic means "store ''unscaled'' register"

msub r0,r1,r2,r3 // load r0 with r3-(r1*r2) (useful for calculating remainders)

mul r0,r1,r2 // load r0 with r1*r2 (actually an alias - see ARM ARM)

push r0 // push r0 onto the stack