Logical & Bitwise instructions ============================== Document conventions -------------------- Notation: ``Rd, Rn`` denote ARM registers R0-R7 except in the case of the special instructions where R0-R15 may be used. ``Rn`` denotes an ARM register whose contents must lie in range ``a <= contents <= b``. In the case of instructions with two register arguments, it is permissible for them to be identical. For example the following will zero R0 (Python ``R0 ^= R0``) regardless of its initial contents. * eor(r0, r0) These instructions affect the condition flags except where stated. Logical instructions -------------------- * and\_(Rd, Rn) ``Rd &= Rn`` * orr(Rd, Rn) ``Rd |= Rn`` * eor(Rd, Rn) ``Rd ^= Rn`` * mvn(Rd, Rn) ``Rd = Rn ^ 0xffffffff`` i.e. Rd = 1's complement of Rn * bic(Rd, Rn) ``Rd &= ~Rn`` bit clear Rd using mask in Rn Note the use of "and\_" instead of "and", because "and" is a reserved keyword in Python. Shift and rotation instructions ------------------------------- * lsl(Rd, Rn<0-31>) ``Rd <<= Rn`` * lsr(Rd, Rn<1-32>) ``Rd = (Rd & 0xffffffff) >> Rn`` Logical shift right * asr(Rd, Rn<1-32>) ``Rd >>= Rn`` arithmetic shift right * ror(Rd, Rn<1-31>) ``Rd = rotate_right(Rd, Rn)`` Rd is rotated right Rn bits. A rotation by (for example) three bits works as follows. If Rd initially contains bits ``b31 b30..b0`` after rotation it will contain ``b2 b1 b0 b31 b30..b3`` Special instructions -------------------- Condition codes are unaffected by these instructions. * clz(Rd, Rn) ``Rd = count_leading_zeros(Rn)`` count_leading_zeros(Rn) returns the number of binary zero bits before the first binary one bit in Rn. * rbit(Rd, Rn) ``Rd = bit_reverse(Rn)`` bit_reverse(Rn) returns the bit-reversed contents of Rn. If Rn contains bits ``b31 b30..b0`` Rd will be set to ``b0 b1 b2..b31`` Trailing zeros may be counted by performing a bit reverse prior to executing clz.