Download Limits on Computing: Understanding Large Numbers and Floating-Point Arithmetic and more Slides Artificial Intelligence in PDF only on Docsity! 1 CSCI 100 Think Like Computers Lecture 3 Fall 2008 Linux • ls [file-or-dir] • ls –l [file-or-dir] • cd directorypath • mkdir dir • rmdir dir • cp … (copy) • mv … (move, rename) • rm … (remove) • Path: dir/subdir/subsubdir • Special file/dir: . and .. ~, ~username • Wildcards * ? • Help: man … Remote Login • Use secure shell (ssh) to connect to csgateway.clarku.edu • Use secure ftp (sftp) to transfer files (download/upload) Homework • Create your own homepage Create the directory ~/public_html Create the file ~/public_html/index.html Change the permissions so that they are accessible to others chmod Change file access mode • chmod : change read, write, execute/directory search permissions for user/group/others • -rwxrwxrwx and drwxrwxrwx -rw------ means the file is not executable, can be read/write by the user (owner only) drwxr-xr-x means the directory can be read/searched by everyone, but modified only by owner • So, all web pages/files should be -rw-r--r--, and all web directory should be drwx--x--x • This is done by: chmod go+r file_name chmod go+x directory_name • There are limitations imposed by the hardware on the representations of both integer numbers and real numbers If the word length is 32 bits, the range of integer numbers that can be represented is -2,147,483,648 to 2,147,483,647 There are software solutions, however, that allow programs to overcome these limitations For example, we could represent a very large number as a list of smaller numbers Limits on Arithmetic Docsity.com 2 Limits on Arithmetic Representing very large numbers Limits on Arithmetic Real numbers are stored as an integer along with information showing the location of the radix point • Let’s assume that we have a computer in which each memory location is the same size and is divided into a sign plus five decimal digits • When a real variable is declared or a real constant is defined, the number stored there has both a whole number part and a fractional part Limits on Arithmetic • The range of the numbers we can represent with five digits is -99,999 through +99,999: Limits on Arithmetic • The precision (the maximum number of digits that can be represented) is five digits, and each number within that range can be represented exactly • What happens if we allow one of these digits (let’s say the leftmost one, in red) to represent an exponent? • For example represents the number +2,345 * 103 Limits on Arithmetic • The range of numbers we can now represent is much larger: -9,999 * 109 to +9,999 * 109 or -9,999,000,000,000 to +9,999,000,000,000 • We can represent only four significant digits Limits on Arithmetic • The four leftmost digits are correct, and the balance of the digits are assumed to be zero • We lose the rightmost, or least significant, digits Docsity.com
