Articles from January, 2009

Print Precision of Dyadic Fractions Varies by Language

By Rick Regan (Published January 30th, 2009)

Interestingly, programming languages vary in how much precision they allow in printed floating-point fractions. You would think they’d all be the same, allowing you to print as many decimal places as you ask for. After all, a floating-point fraction is a dyadic fraction; it has as many decimal places as it has bits in its fractional representation.

Consider the dyadic fraction 5,404,319,552,844,595/2⁵³. Its decimal expansion is 0.59999999999999997779553950749686919152736663818359375, and its binary expansion is 0.10011001100110011001100110011001100110011001100110011. Both are 53 digits long. The ideal programming language lets you print all 53 decimal places, because all are meaningful. Unfortunately, many languages won’t let you do that; they typically cap the number of decimal places at between 15 and 17, which for our example might be 0.59999999999999998.

Ten Ways to Check if an Integer Is a Power Of Two in C

By Rick Regan (Published January 18th, 2009)

To write a program to check if an integer is a power of two, you could follow two basic strategies: check the number based on its decimal value, or check it based on its binary representation. The former approach is more human-friendly but generally less efficient; the latter approach is more machine-friendly but generally more efficient. We will explore both approaches, comparing ten different but equivalent C functions.

What Powers of Two Look Like Inside a Computer

By Rick Regan (Published January 7th, 2009)

A power of two, when expressed as a binary number, is easy to spot: it has one, and only one, 1 bit. For example, 1000, 10, and 0.001 are powers of two. Inside a computer, however, numbers are more generally represented in binary code, not as “pure” binary numbers. As a result, you may not be able to look at the binary representation of a number and tell at a glance whether it’s a power of two or not; it depends on how it’s encoded.

A Twelve Cent Binary Calendar

By Rick Regan (Published January 1st, 2009)

Do you have twelve coins handy? You can lay them out on a piece of cardboard to keep track of the month, day, and day of the week, as shown here at Evil Mad Scientist Laboratories. Here’s the one I made: