#14059: Fix refcount/deallocation of integers
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Reporter: SimonKing | Owner: rlm
Type: defect | Status: new
Priority: blocker | Milestone: sage-5.7
Component: memleak | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
At least for educational purposes, the following comments have to change:
{{{
# We take the address 'new' and move mpz_t_offset bytes (chars)
# to the address of 'value'. We treat that address as a pointer
# to a mpz_t struct and allocate memory for the _mp_d element of
# that struct. We allocate one limb.
#
# What is done here is potentially very dangerous as it reaches
# deeply into the internal structure of GMP. Consequently things
# may break if a new release of GMP changes some internals. To
# emphasize this, this is what the GMP manual has to say about
# the documentation for the struct we are using:
#
# "This chapter is provided only for informational purposes and
the
# various internals described here may change in future GMP
releases.
# Applications expecting to be compatible with future releases
should use
# only the documented interfaces described in previous chapters."
#
# If this line is used Sage is not such an application.
#
# The clean version of the following line is:
#
# mpz_init( <mpz_t>(<char *>new + mpz_t_offset) )
#
# We save time both by avoiding an extra function call and
# because the rest of the mpz struct was already initialized
# fully using the memcpy above.
(<__mpz_struct *>( <char *>new + mpz_t_offset) )._mp_d =
<mp_ptr>mpz_alloc(GMP_LIMB_BITS >> 3)
}}}
Namely, when I uncomment `mpz_init( <mpz_t>(<char *>new + mpz_t_offset) )`
and comment the last line, then the module won't build:
{{{
sage/rings/integer.c: In function
‘__pyx_f_4sage_5rings_7integer_fast_tp_new’:
sage/rings/integer.c:35637:18: error: cast specifies array type
error: command 'gcc' failed with exit status 1
Error installing modified sage library code.
}}}
So, the "clean version" doesn't even build.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14059#comment:11>
Sage <http://www.sagemath.org>
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