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'''
This module contains helper classes for alignment arithmetic and checks
'''
from fractions import gcd
class Alignment(object):
def __init__(self, align=4, offset=0):
self.align = align
# normalize the offset (just in case)
self.offset = offset % align
def __eq__(self, other):
return self.align == other.align and self.offset == other.offset
def __str__(self):
return "(align=%d, offset=%d)" % (self.align, self.offset)
@staticmethod
def for_primitive_type(size):
# compute the required start_alignment based on the size of the type
if size % 8 == 0:
# do 8-byte primitives require 8-byte alignment in X11?
return Alignment(8,0)
elif size % 4 == 0:
return Alignment(4,0)
elif size % 2 == 0:
return Alignment(2,0)
else:
return Alignment(1,0)
def align_after_fixed_size(self, size):
new_offset = (self.offset + size) % self.align
return Alignment(self.align, new_offset)
def is_guaranteed_at(self, external_align):
'''
Assuming the given external_align, checks whether
self is fulfilled for all cases.
Returns True if yes, False otherwise.
'''
if self.align == 1 and self.offset == 0:
# alignment 1 with offset 0 is always fulfilled
return True
if external_align is None:
# there is no external align -> fail
return False
if external_align.align < self.align:
# the external align guarantees less alignment -> not guaranteed
return False
if external_align.align % self.align != 0:
# the external align cannot be divided by our align
# -> not guaranteed
# (this can only happen if there are alignments that are not
# a power of 2, which is highly discouraged. But better be
# safe and check for it)
return False
if external_align.offset % self.align != self.offset:
# offsets do not match
return False
return True
def combine_with(self, other):
# returns the alignment that is guaranteed when
# both, self or other, can happen
new_align = gcd(self.align, other.align)
new_offset_candidate1 = self.offset % new_align
new_offset_candidate2 = other.offset % new_align
if new_offset_candidate1 == new_offset_candidate2:
new_offset = new_offset_candidate1
else:
offset_diff = abs(new_offset_candidate2 - new_offset_candidate1)
new_align = gcd(new_align, offset_diff)
new_offset_candidate1 = self.offset % new_align
new_offset_candidate2 = other.offset % new_align
assert new_offset_candidate1 == new_offset_candidate2
new_offset = new_offset_candidate1
# return the result
return Alignment(new_align, new_offset)
class AlignmentLog(object):
def __init__(self):
self.ok_list = []
self.fail_list = []
self.verbosity = 1
def __str__(self):
result = ""
# output the OK-list
for (align_before, field_name, type_obj, callstack, align_after) in self.ok_list:
stacksize = len(callstack)
indent = ' ' * stacksize
if self.ok_callstack_is_relevant(callstack):
if field_name is None or field_name == "":
result += (" %sok: %s:\n\t%sbefore: %s, after: %s\n"
% (indent, str(type_obj), indent, str(align_before), str(align_after)))
else:
result += (" %sok: field \"%s\" in %s:\n\t%sbefore: %s, after: %s\n"
% (indent, str(field_name), str(type_obj),
indent, str(align_before), str(align_after)))
if self.verbosity >= 1:
result += self.callstack_to_str(indent, callstack)
# output the fail-list
for (align_before, field_name, type_obj, callstack, reason) in self.fail_list:
stacksize = len(callstack)
indent = ' ' * stacksize
if field_name is None or field_name == "":
result += (" %sfail: align %s is incompatible with\n\t%s%s\n\t%sReason: %s\n"
% (indent, str(align_before), indent, str(type_obj), indent, reason))
else:
result += (" %sfail: align %s is incompatible with\n\t%sfield \"%s\" in %s\n\t%sReason: %s\n"
% (indent, str(align_before), indent, str(field_name), str(type_obj), indent, reason))
if self.verbosity >= 1:
result += self.callstack_to_str(indent, callstack)
return result
def callstack_to_str(self, indent, callstack):
result = "\t%scallstack: [\n" % indent
for stack_elem in callstack:
result += "\t %s%s\n" % (indent, str(stack_elem))
result += "\t%s]\n" % indent
return result
def ok_callstack_is_relevant(self, ok_callstack):
# determine whether an ok callstack is relevant for logging
if self.verbosity >= 2:
return True
# empty callstacks are always relevant
if len(ok_callstack) == 0:
return True
# check whether the ok_callstack is a subset or equal to a fail_callstack
for (align_before, field_name, type_obj, fail_callstack, reason) in self.fail_list:
if len(ok_callstack) <= len(fail_callstack):
zipped = zip(ok_callstack, fail_callstack[:len(ok_callstack)])
is_subset = all([i == j for i, j in zipped])
if is_subset:
return True
return False
def ok(self, align_before, field_name, type_obj, callstack, align_after):
self.ok_list.append((align_before, field_name, type_obj, callstack, align_after))
def fail(self, align_before, field_name, type_obj, callstack, reason):
self.fail_list.append((align_before, field_name, type_obj, callstack, reason))
def append(self, other):
self.ok_list.extend(other.ok_list)
self.fail_list.extend(other.fail_list)
def ok_count(self):
return len(self.ok_list)
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