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;
if (mpfr.mpfr_number_p(bf) and
not mpfr.mpfr_zero_p(bf) and
mpfr.mpfr_get_exp(bf) < context.precision - 1 + context.emin):
mpfr.mpfr_set_underflow()
ternary = mpfr.mpfr_subnormalize(bf, ternary, rounding)
if ternary:
mpfr.mpfr_set_inexflag()
return bf
