hru(1): adds more descriptive comments

src/hru.rs

@@ -29,40 +29,45 @@ extern crate sysexits;
 use strerror::StrError;
 use sysexits::{ EX_DATAERR, EX_IOERR, EX_SOFTWARE };
 
+/* list of SI prefixes */
 const LIST: [(u32, &str); 10] = [
-	(3, "k"),
-	(6, "M"),
-	(9, "G"),
-	(12, "T"),
-	(15, "P"),
-	(18, "E"),
-	(21, "Z"),
-	(24, "Y"),
-	(27, "R"),
-	(30, "Q")
+	(3, "k"), /* kilo */
+	(6, "M"), /* mega */
+	(9, "G"), /* giga */
+	(12, "T"), /* tera */
+	(15, "P"), /* peta */
+	(18, "E"), /* exa */
+	(21, "Z"), /* zetta */
+	(24, "Y"), /* yotta */
+	(27, "R"), /* ronna */
+	(30, "Q"), /* quetta */
 ];
 
 fn convert(input: u128) -> Result<(f64, (u32, &'static str)), String> {
-
+	/* preserve decimal places in output by casting to a float */
 	let mut out = (input as f64, (0_u32, "")); 
-	if input < 1000 { return Ok(out); }
+
+	if input < 1000 { return Ok(out); } /* too low to convert */
 
 	for (n, p) in LIST {
 		let c = match 10_u128.checked_pow(n) {
 			Some(c) => c,
-			None => {
+			None => { /* too big for the laws of computing :( */
 				return Err(format!("10^{}: Integer overflow", n.to_string()));
 			},
 		};
 
 		match c.cmp(&input) {
-			Ordering::Less => {
+			Ordering::Less => { /* c < input */
+				/* the program will keep assigning out every loop until either
+				 * the list runs out of higher prefix bases or the input is
+				 * greater than the prefix base */
 				out = (input as f64 / c as f64, (n, p));
 			},
-			Ordering::Equal => {
+			Ordering::Equal => { /* c == input */
 				return Ok((input as f64 / c as f64, (n, p)));
 			},
-			Ordering::Greater => {},
+			Ordering::Greater => {}, /* c > input */
 		};
 	}
 
@@ -72,6 +77,7 @@ fn convert(input: u128) -> Result<(f64, (u32, &'static str)), String> {
 fn main() -> ExitCode {
 	let argv = args().collect::<Vec<String>>();
 	let mut buf = String::new();
+
 	while let Ok(_) = stdin().read_line(&mut buf) {
 		if buf.is_empty() { return ExitCode::SUCCESS; }
 
@@ -96,6 +102,7 @@ fn main() -> ExitCode {
 
 		let si_prefix = format!("{}B", prefix.1);
 
+		/* round output number to one decimal place */
 		let out = ((number * 10.0).round() / 10.0).to_string();
 
 		stdout().write_all(format!("{} {}\n", out, si_prefix).as_bytes())