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