kopia lustrzana https://github.com/micropython/micropython
54 wiersze
1.9 KiB
ReStructuredText
54 wiersze
1.9 KiB
ReStructuredText
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<a-b>`` 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.
|