Added hexdump UPROG

Makefile

@@ -170,6 +170,7 @@ UPROGS=\
 	_echo\
 	_forktest\
 	_grep\
+	_hexdump\
 	_init\
 	_kill\
 	_ln\

hexdump.c

@@ -0,0 +1,138 @@
+#include "types.h"
+#include "stat.h"
+#include "user.h"
+
+//change this to change how many hex/ascii per line
+#define CHAR_COUNT 16
+#define LC_PER_CONTINUE 16
+
+static void
+ctoahex(char val, char buf[2])
+{
+	char l = (val & 0xF);
+	buf[1] = (l <= 9 ? ('0' + l) : ('A' + l - 10));
+	char h = (val & 0xF0) >> 4;
+	buf[0] = (h <= 9 ? ('0' + h) : ('A' + h - 10));
+}
+
+static void
+print_swath(const char* swath, int count)
+{
+	char hbuf[3] = { 'X', 'X', ' ' }; //index 2 never modified
+	//hex values
+	for (int i = 0; i < count; i++)
+	{
+		ctoahex(swath[i], hbuf);
+		if (write(1, hbuf, 3) != 3)
+		{
+			printf(1, "hexdump: write error 1\n");
+			exit();
+		}
+		if (i % 4 == 3) //print extra gap every 4
+		{
+			hbuf[0] = ' ';
+			hbuf[1] = ' ';
+			if (write(1, hbuf, 3) != 3)
+			{
+				printf(1, "hexdump: write error 2\n");
+				exit();
+			}
+		}
+	}
+	//fill in empty hex spaces
+	hbuf[0] = ' ';
+	hbuf[1] = ' ';
+	//spacing + missed "extra gap every 4" (little gap between hex and ascii)
+	for (int i = 0; i < (CHAR_COUNT - count) + (4 - (count / 4)); i++)
+	{
+		if (write(1, hbuf, 3) != 3)
+		{
+			printf(1, "hexdump: write error 3\n");
+			exit();
+		}
+	}
+	//ascii values
+	for (int i = 0; i < count; i++)
+	{
+		char bf[1] = { swath[i] };
+		if ((bf[0] < '!' || bf[0] > '~') && bf[0] != ' ')
+			bf[0] = '.';
+		if (write(1, bf, 1) != 1)
+		{
+			printf(1, "hexdump: write error 4\n");
+			exit();
+		}
+	}
+	char nl[1] = { '\n' };
+	if (write(1, nl, 1) != 1)
+	{
+		printf(1, "hexdump: write error 5\n");
+		exit();
+	}
+
+//bad:
+//	printf(1, "hexdump: write error\n");
+//	exit();
+}
+
+char buf[512];
+
+void
+hexdump(int fd)
+{
+	int n;
+
+	while((n = read(fd, buf, sizeof(buf))) > 0) {
+
+		const char rem = n % CHAR_COUNT;
+		for (int chunk = 0, lc = 0; chunk < n - rem; chunk += CHAR_COUNT, lc++)
+		{
+			char* section = buf + chunk;
+			print_swath(section, CHAR_COUNT);
+			if (lc >= LC_PER_CONTINUE)
+			{
+				printf(1, "Enter to continue, or type anything followed by enter to quit.\n");
+				char ri[1] ={ '\n' };
+				if (read(0, ri, sizeof(ri)) < 0 || ri[0] != '\n')
+				{
+					//consume all of standard input (so xv6 doesn't try to exec it).
+					//technechally, if the user does a multiple of 512 chars as input, 
+					//you need to type something & hit enter a second time.
+					//This is done this way because there doesn't seem to be a way to
+					//clear the stdin and/or a pipe. Perhaps add a syscall? Idk.
+					while ((n = read(0, buf, sizeof(buf))) == sizeof(buf))
+						;
+					exit();
+				}
+				lc = 0;
+			}
+		}
+		if (rem > 0)
+			print_swath(buf + (n - rem), rem);
+	}
+	if (n < 0) {
+		printf(1, "hexdump: read error\n");
+		exit();
+	}
+}
+
+int
+main(int argc, char* argv[])
+{
+	int fd, i;
+
+	if (argc <= 1) {
+		printf(1, "hexdump: need file argument\n");
+		exit();
+	}
+
+	for (i = 1; i < argc; i++) {
+		if ((fd = open(argv[i], 0)) < 0) {
+			printf(1, "hexdump: cannot open %s\n", argv[i]);
+			exit();
+		}
+		hexdump(fd);
+		close(fd);
+	}
+	exit();
+}