295 lines
8.9 KiB
Python
295 lines
8.9 KiB
Python
"""
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Cretonne predicates.
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A *predicate* is a function that computes a boolean result. The inputs to the
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function determine the kind of predicate:
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- An *ISA predicate* is evaluated on the current ISA settings together with the
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shared settings defined in the :py:mod:`settings` module. Once a target ISA
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has been configured, the value of all ISA predicates is known.
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- An *Instruction predicate* is evaluated on an instruction instance, so it can
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inspect all the immediate fields and type variables of the instruction.
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Instruction predicates can be evaluated before register allocation, so they
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can not depend on specific register assignments to the value operands or
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outputs.
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Predicates can also be computed from other predicates using the `And`, `Or`,
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and `Not` combinators defined in this module.
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All predicates have a *context* which determines where they can be evaluated.
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For an ISA predicate, the context is the ISA settings group. For an instruction
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predicate, the context is the instruction format.
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"""
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from __future__ import absolute_import
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from functools import reduce
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try:
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from typing import Sequence, Tuple, Set, Any, Union, TYPE_CHECKING # noqa
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if TYPE_CHECKING:
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from .formats import InstructionFormat, FormatField # noqa
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from .settings import BoolSetting, SettingGroup # noqa
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PredContext = Union[SettingGroup, InstructionFormat]
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PredLeaf = Union[BoolSetting, 'FieldPredicate']
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PredNode = Union[PredLeaf, 'Predicate']
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except ImportError:
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pass
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def _is_parent(a, b):
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# type: (PredContext, PredContext) -> bool
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"""
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Return true if a is a parent of b, or equal to it.
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"""
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while b and a is not b:
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b = getattr(b, 'parent', None)
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return a is b
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def _descendant(a, b):
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# type: (PredContext, PredContext) -> PredContext
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"""
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If a is a parent of b or b is a parent of a, return the descendant of the
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two.
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If neiher is a parent of the other, return None.
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"""
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if _is_parent(a, b):
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return b
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if _is_parent(b, a):
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return a
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return None
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class Predicate(object):
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"""
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Superclass for all computed predicates.
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Leaf predicates can have other types, such as `Setting`.
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:param parts: Tuple of components in the predicate expression.
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"""
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def __init__(self, parts):
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# type: (Sequence[PredNode]) -> None
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self.name = None # type: str
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self.number = None # type: int
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self.parts = parts
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self.context = reduce(
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_descendant,
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(p.predicate_context() for p in parts))
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assert self.context, "Incompatible predicate parts"
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def __str__(self):
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# type: () -> str
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if self.name:
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return '{}.{}'.format(self.context.name, self.name)
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else:
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return '{}({})'.format(
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type(self).__name__,
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', '.join(map(str, self.parts)))
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def predicate_context(self):
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# type: () -> PredContext
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return self.context
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def predicate_leafs(self, leafs):
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# type: (Set[PredLeaf]) -> None
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"""
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Collect all leaf predicates into the `leafs` set.
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"""
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for part in self.parts:
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part.predicate_leafs(leafs)
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def rust_predicate(self, prec):
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# type: (int) -> str
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raise NotImplementedError("rust_predicate is an abstract method")
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class And(Predicate):
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"""
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Computed predicate that is true if all parts are true.
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"""
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precedence = 2
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def __init__(self, *args):
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# type: (*PredNode) -> None
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super(And, self).__init__(args)
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def rust_predicate(self, prec):
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# type: (int) -> str
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"""
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Return a Rust expression computing the value of this predicate.
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The surrounding precedence determines whether parentheses are needed:
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0. An `if` statement.
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1. An `||` expression.
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2. An `&&` expression.
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3. A `!` expression.
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"""
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s = ' && '.join(p.rust_predicate(And.precedence) for p in self.parts)
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if prec > And.precedence:
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s = '({})'.format(s)
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return s
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@staticmethod
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def combine(*args):
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# type: (*PredNode) -> PredNode
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"""
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Combine a sequence of predicates, allowing for `None` members.
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Return a predicate that is true when all non-`None` arguments are true,
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or `None` if all of the arguments are `None`.
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"""
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args = tuple(p for p in args if p)
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if args == ():
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return None
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if len(args) == 1:
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return args[0]
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# We have multiple predicate args. Combine with `And`.
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return And(*args)
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class Or(Predicate):
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"""
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Computed predicate that is true if any parts are true.
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"""
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precedence = 1
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def __init__(self, *args):
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# type: (*PredNode) -> None
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super(Or, self).__init__(args)
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def rust_predicate(self, prec):
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# type: (int) -> str
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s = ' || '.join(p.rust_predicate(Or.precedence) for p in self.parts)
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if prec > Or.precedence:
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s = '({})'.format(s)
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return s
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class Not(Predicate):
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"""
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Computed predicate that is true if its single part is false.
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"""
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precedence = 3
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def __init__(self, part):
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# type: (PredNode) -> None
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super(Not, self).__init__((part,))
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def rust_predicate(self, prec):
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# type: (int) -> str
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return '!' + self.parts[0].rust_predicate(Not.precedence)
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class FieldPredicate(object):
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"""
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An instruction predicate that performs a test on a single `FormatField`.
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:param field: The `FormatField` to be tested.
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:param function: Boolean predicate function to call.
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:param args: Additional arguments for the predicate function.
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"""
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def __init__(self, field, function, args):
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# type: (FormatField, str, Sequence[Any]) -> None
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self.number = None # type: int
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self.field = field
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self.function = function
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self.args = args
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# All PredNode members must have a name field. This will never be set.
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self.name = None # type: str
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def __str__(self):
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# type: () -> str
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args = (self.field.name,) + tuple(map(str, self.args))
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return '{}({})'.format(self.function, ', '.join(args))
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def predicate_context(self):
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# type: () -> PredContext
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"""
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This predicate can be evaluated in the context of an instruction
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format.
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"""
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return self.field.format
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def predicate_leafs(self, leafs):
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# type: (Set[PredLeaf]) -> None
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leafs.add(self)
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def rust_predicate(self, prec):
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# type: (int) -> str
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"""
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Return a string of Rust code that evaluates this predicate.
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"""
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# Prepend `field` to the predicate function arguments.
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args = (self.field.rust_name(),) + tuple(map(str, self.args))
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return 'predicates::{}({})'.format(self.function, ', '.join(args))
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class IsEqual(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is equal to a constant value.
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:param field: `FormatField` to be checked.
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:param value: The constant value to compare against.
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"""
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def __init__(self, field, value):
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# type: (FormatField, Any) -> None
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super(IsEqual, self).__init__(field, 'is_equal', (value,))
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self.value = value
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class IsSignedInt(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is representable as an n-bit two's complement integer.
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:param field: `FormatField` to be checked.
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:param width: Number of bits in the allowed range.
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:param scale: Number of low bits that must be 0.
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The predicate is true if the field is in the range:
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`-2^(width-1) -- 2^(width-1)-1`
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and a multiple of `2^scale`.
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"""
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def __init__(self, field, width, scale=0):
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# type: (FormatField, int, int) -> None
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super(IsSignedInt, self).__init__(
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field, 'is_signed_int', (width, scale))
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self.width = width
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self.scale = scale
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assert width >= 0 and width <= 64
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assert scale >= 0 and scale < width
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class IsUnsignedInt(FieldPredicate):
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"""
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Instruction predicate that checks if an immediate instruction format field
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is representable as an n-bit unsigned complement integer.
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:param field: `FormatField` to be checked.
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:param width: Number of bits in the allowed range.
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:param scale: Number of low bits that must be 0.
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The predicate is true if the field is in the range:
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`0 -- 2^width - 1` and a multiple of `2^scale`.
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"""
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def __init__(self, field, width, scale=0):
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# type: (FormatField, int, int) -> None
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super(IsUnsignedInt, self).__init__(
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field, 'is_unsigned_int', (width, scale))
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self.width = width
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self.scale = scale
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assert width >= 0 and width <= 64
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assert scale >= 0 and scale < width
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