Allow friendly partition sizing:

  a foo . .+600M

creates a 600MB partition. The parser recognizes
K, M, G, and T (and the corresponding lowercase variants)
as viable suffixes. The scaling is binary, not decimal.

Reference: /n/sources/patch/applied/prep-scaling
Date: Wed Sep 23 23:35:16 CES 2009
Signed-off-by: lyndon@orthanc.ca

--- /sys/src/cmd/disk/prep/calc.y	Wed Sep 23 23:29:20 2009
+++ /sys/src/cmd/disk/prep/calc.y	Wed Sep 23 23:29:18 2009
@@ -85,6 +85,8 @@
 static int
 yylex(void)
 {
+	vlong n;
+
 	while(isspace(*inp))
 		inp++;
 
@@ -92,7 +94,26 @@
 		return 0;
 
 	if(isdigit(*inp)) {
-		yylval = mkNUM(strtoll(inp, &inp, 0));
+		n = strtoll(inp, &inp, 0);
+		switch(*inp) {
+		case 'k':
+		case 'K': 	n *= 2;
+					inp++;
+					break;
+		case 'm':
+		case 'M': 	n *= (1024*2);
+					inp++;
+					break;
+		case 'g':
+		case 'G': 	n *= (1024*1024*2);
+					inp++;
+					break;
+		case 't':
+		case 'T': 	n *= (1024LL*1024*1024*2);
+					inp++;
+					break;
+		}
+		yylval = mkNUM(n);
 		return NUMBER;
 	}
 
--- /sys/man/8/prep	Wed Sep 23 23:29:25 2009
+++ /sys/man/8/prep	Wed Sep 23 23:29:22 2009
@@ -364,6 +364,10 @@
 .I end
 can take on without running off the disk
 or into another partition.
+Numeric constants suffixed by
+K, M, G, or T
+are scaled to the respective size in kilo-, mega-, giga-,
+or terabytes.
 Finally, the expression
 .IB n %
 evaluates to
@@ -375,6 +379,12 @@
 creates a new partition starting at
 .B .
 that takes up a fifth of the disk,
+.B a
+.B .
+.B .+21G
+creates a new partition starting at
+.B .
+that takes up 21 gigabytes (21 × 2^30 bytes),
 and
 .B a
 .B 1000