def _apply_function_in_context(cls, f, args, context):
""" Apply an MPFR function 'f' to the given arguments 'args', rounding to
the given context. Returns a new Mpfr object with precision taken from
the current context.
"""
rounding = context.rounding
bf = mpfr.Mpfr_t.__new__(cls)
mpfr.mpfr_init2(bf, context.precision)
args = (bf,) + args + (rounding,)
ternary = f(*args)
with _temporary_exponent_bounds(context.emin, context.emax):
ternary = mpfr.mpfr_check_range(bf, ternary, rounding)
if context.subnormalize:
# mpfr_subnormalize doesn't set underflow and
# subnormal flags, so we do that ourselves. We choose
# to set the underflow flag for *all* cases where the
# 'after rounding' result is smaller than the smallest
# normal number, even if that result is exact.
# if bf is zero but ternary is nonzero, the underflow
# flag will already have been set by mpfr_check_range;
underflow = (
mpfr.mpfr_number_p(bf) and
not mpfr.mpfr_zero_p(bf) and
mpfr.mpfr_get_exp(bf) < context.precision - 1 + context.emin)
if underflow:
mpfr.mpfr_set_underflow()
ternary = mpfr.mpfr_subnormalize(bf, ternary, rounding)
if ternary:
mpfr.mpfr_set_inexflag()
return bf
def _apply_function_in_context(cls, f, args, context):
""" Apply an MPFR function 'f' to the given arguments 'args', rounding to
the given context. Returns a new Mpfr object with precision taken from
the current context.
"""
rounding = context.rounding
bf = mpfr.Mpfr_t.__new__(cls)
mpfr.mpfr_init2(bf, context.precision)
args = (bf,) + args + (rounding,)
ternary = f(*args)
with _temporary_exponent_bounds(context.emin, context.emax):
ternary = mpfr.mpfr_check_range(bf, ternary, rounding)
if context.subnormalize:
# mpfr_subnormalize doesn't set underflow and
# subnormal flags, so we do that ourselves. We choose
# to set the underflow flag for *all* cases where the
# 'after rounding' result is smaller than the smallest
# normal number, even if that result is exact.
# if bf is zero but ternary is nonzero, the underflow
# flag will already have been set by mpfr_check_range;
underflow = (
mpfr.mpfr_number_p(bf) and
not mpfr.mpfr_zero_p(bf) and
mpfr.mpfr_get_exp(bf) < context.precision - 1 + context.emin)
if underflow:
mpfr.mpfr_set_underflow()
ternary = mpfr.mpfr_subnormalize(bf, ternary, rounding)
if ternary:
mpfr.mpfr_set_inexflag()
return bf
def _quotient_exponent(x, y):
"""
Given two positive finite MPFR instances x and y,
find the exponent of x / y; that is, the unique
integer e such that 2**(e-1) <= x / y < 2**e.
"""
assert mpfr.mpfr_regular_p(x)
assert mpfr.mpfr_regular_p(y)
# Make copy of x with the exponent of y.
x2 = mpfr.Mpfr_t()
mpfr.mpfr_init2(x2, mpfr.mpfr_get_prec(x))
mpfr.mpfr_set(x2, x, mpfr.MPFR_RNDN)
mpfr.mpfr_set_exp(x2, mpfr.mpfr_get_exp(y))
# Compare x2 and y, disregarding the sign.
extra = mpfr.mpfr_cmpabs(x2, y) >= 0
return extra + mpfr.mpfr_get_exp(x) - mpfr.mpfr_get_exp(y)
