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Merged
merged 1 commit into from
Oct 14, 2023
Merged

fix(fmpz_mod): avoid using malloc/free #95

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8 changes: 5 additions & 3 deletions src/flint/types/fmpz_mod.pxd
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Original file line number Diff line number Diff line change
Expand Up @@ -8,12 +8,14 @@ from flint.flintlib.fmpz_mod cimport (
cdef class fmpz_mod_ctx:
cdef fmpz_mod_ctx_t val
cdef bint _is_prime
cdef fmpz_mod_discrete_log_pohlig_hellman_t *L
cdef bint _init_L
cdef fmpz_mod_discrete_log_pohlig_hellman_t L

cdef set_any_as_fmpz_mod(self, fmpz_t val, obj)
cdef any_as_fmpz_mod(self, obj)
cdef _precompute_dlog_prime(self)
cdef discrete_log_pohlig_hellman_run(self, fmpz_t x, fmpz_t y)

cdef class fmpz_mod(flint_scalar):
cdef fmpz_mod_ctx ctx
cdef fmpz_t val
cdef fmpz_t *x_g
cdef fmpz_t x_g
63 changes: 22 additions & 41 deletions src/flint/types/fmpz_mod.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ from flint.flintlib.fmpz cimport(
fmpz_divexact,
fmpz_gcd,
fmpz_is_one,
fmpz_is_zero,
fmpz_randm
)
from flint.flintlib.fmpz cimport fmpz_mod as fmpz_type_mod
Expand Down Expand Up @@ -41,14 +42,12 @@ cdef class fmpz_mod_ctx:
cdef fmpz one = fmpz.__new__(fmpz)
fmpz_one(one.val)
fmpz_mod_ctx_init(self.val, one.val)
self.L = NULL
fmpz_mod_discrete_log_pohlig_hellman_clear(self.L)
self._is_prime = 0


def __dealloc__(self):
fmpz_mod_ctx_clear(self.val)
if self.L:
fmpz_mod_discrete_log_pohlig_hellman_clear(self.L[0])
fmpz_mod_discrete_log_pohlig_hellman_clear(self.L)

def __init__(self, mod):
# Ensure modulus is fmpz type
Expand Down Expand Up @@ -137,18 +136,15 @@ cdef class fmpz_mod_ctx:

return res

cdef _precompute_dlog_prime(self):
"""
Initalise the dlog data, all discrete logs are solved with an
internally chosen base `y`
"""
self.L = <fmpz_mod_discrete_log_pohlig_hellman_t *>libc.stdlib.malloc(
cython.sizeof(fmpz_mod_discrete_log_pohlig_hellman_struct)
)
fmpz_mod_discrete_log_pohlig_hellman_init(self.L[0])
fmpz_mod_discrete_log_pohlig_hellman_precompute_prime(
self.L[0], self.val.n
)
cdef discrete_log_pohlig_hellman_run(self, fmpz_t x, fmpz_t y):
# First, Ensure that L has performed precomputations This generates a
# base which is a primative root, and used as the base in
# fmpz_mod_discrete_log_pohlig_hellman_run
if not self._init_L:
fmpz_mod_discrete_log_pohlig_hellman_precompute_prime(self.L, self.val.n)
self._init_L = True

fmpz_mod_discrete_log_pohlig_hellman_run(x, self.L, y)

cdef set_any_as_fmpz_mod(self, fmpz_t val, obj):
# Try and convert obj to fmpz
Expand Down Expand Up @@ -235,13 +231,11 @@ cdef class fmpz_mod(flint_scalar):

def __cinit__(self):
fmpz_init(self.val)
self.x_g = NULL
fmpz_init(self.x_g)

def __dealloc__(self):
fmpz_clear(self.val)
if self.x_g:
fmpz_clear(self.x_g[0])
libc.stdlib.free(self.x_g)
fmpz_clear(self.x_g)

def __init__(self, val, ctx):
if not typecheck(ctx, fmpz_mod_ctx):
Expand Down Expand Up @@ -354,33 +348,20 @@ cdef class fmpz_mod(flint_scalar):
if a is NotImplemented:
raise TypeError(f"Cannot solve the discrete log with {type(a)} as input")

# First, Ensure that self.ctx.L has performed precomputations
# This generates a `y` which is a primative root, and used as
# the base in `fmpz_mod_discrete_log_pohlig_hellman_run`
if not self.ctx.L:
self.ctx._precompute_dlog_prime()

# Solve the discrete log for the chosen base and target
# g = y^x_g and a = y^x_a
# We want to find x such that a = g^x =>
# (y^x_a) = (y^x_g)^x => x = (x_a / x_g) mod (p-1)

# For repeated calls to discrete_log, it's more efficient to
# store x_g rather than keep computing it
if not self.x_g:
self.x_g = <fmpz_t *>libc.stdlib.malloc(
cython.sizeof(fmpz_t)
)
fmpz_mod_discrete_log_pohlig_hellman_run(
self.x_g[0], self.ctx.L[0], self.val
)
if fmpz_is_zero(self.x_g):
self.ctx.discrete_log_pohlig_hellman_run(self.x_g, self.val)

# Then we need to compute x_a which will be different for each call
cdef fmpz_t x_a
fmpz_init(x_a)
fmpz_mod_discrete_log_pohlig_hellman_run(
x_a, self.ctx.L[0], (<fmpz_mod>a).val
)
self.ctx.discrete_log_pohlig_hellman_run(x_a, (<fmpz_mod>a).val)

# If g is not a primative root, then x_g and pm1 will share
# a common factor. We can use this to compute the order of
Expand All @@ -390,14 +371,14 @@ cdef class fmpz_mod(flint_scalar):
fmpz_init(g_order)
fmpz_init(x_g)

fmpz_gcd(g, self.x_g[0], self.ctx.L[0].pm1)
fmpz_gcd(g, self.x_g, self.ctx.L.pm1)
if not fmpz_is_one(g):
fmpz_divexact(x_g, self.x_g[0], g)
fmpz_divexact(x_g, self.x_g, g)
fmpz_divexact(x_a, x_a, g)
fmpz_divexact(g_order, self.ctx.L[0].pm1, g)
fmpz_divexact(g_order, self.ctx.L.pm1, g)
else:
fmpz_set(g_order, self.ctx.L[0].pm1)
fmpz_set(x_g, self.x_g[0])
fmpz_set(g_order, self.ctx.L.pm1)
fmpz_set(x_g, self.x_g)

# Finally, compute output exponent by computing
# (x_a / x_g) mod g_order
Expand Down