Coverage for local/lib/python2.7/site-packages/sage/arith/numerical_approx.pxd : 78%

cpdef inline long digits_to_bits(d) except -1: 

""" 

EXAMPLES:: 

sage: from sage.arith.numerical_approx import digits_to_bits 

sage: digits_to_bits(None) 

53 

sage: digits_to_bits(15) 

54 

sage: digits_to_bits(-1) 

Traceback (most recent call last): 

... 

ValueError: number of digits must be positive 

sage: digits_to_bits("10") 

Traceback (most recent call last): 

... 

TypeError: a float is required 

""" 

if d is None: 

return 53 

cdef double x = d 

if x <= 0: 

raise ValueError("number of digits must be positive") 

# Add 1 because of the way how we display real numbers by default 

x += 1 

cdef double LOG_TEN_TWO = 3.321928094887362 

# Add 1 to round up 

return <long>(x * LOG_TEN_TWO) + 1