a8xd: implement -o, -s, -l, add more messages for -v.

3 files changed, 79 insertions, 22 deletions

diff --git a/a8xd.1 b/a8xd.1
index 385983e..1995470 100644
--- a/a8xd.1
+++ b/a8xd.1
@@ -73,7 +73,7 @@ Print XL/XE International Character Set conversions instead of ATASCII.
 .INDENT 0.0
 .TP
 .B \-l \fIlen\fP
-\fB*\fP Stop after dumping \fIlen\fP bytes. \fIlen\fP may be given in decimal or hex (with
+Stop after dumping \fIlen\fP bytes. \fIlen\fP may be given in decimal or hex (with
 leading \fI0x\fP or \fI$\fP).
 .UNINDENT
 .INDENT 0.0
@@ -86,10 +86,12 @@ set are still displayed in inverse.
 .TP
 .B \-o \fIoffset\fP
 Add \fIoffset\fP to displayed file position. \fIoffset\fP can be given in decimal
-or hex (with leading \fI0x\fP or \fI$\fP).
+or hex (with leading \fI0x\fP or \fI$\fP). Negative offsets are allowed, but they
+will be printed as very large positive numbers in the output (this matches
+\fBxxd\fP\(aqs behaviour).
 .TP
 .B \-s \fI[\-]seek\fP
-\fB*\fP Start at \fIseek\fP bytes. Without \fI\-\fP, this is an absolute offset. With \fI\-\fP,
+Start at \fIseek\fP bytes. Without \fI\-\fP, this is an absolute offset. With \fI\-\fP,
 it\(aqs relative to the end of the file. The \fI\-\fP option won\(aqt work when
 reading from standard input. \fIseek\fP may be given in decimal or hex
 (with leading \fI0x\fP or \fI$\fP).
@@ -100,7 +102,8 @@ reading from standard input. \fIseek\fP may be given in decimal or hex
 Use uppercase letters for hex digits; the default is lowercase.
 .TP
 .B  \-v
-Verbose. Currently, this option is accepted, but it doesn\(aqt do anything yet.
+Verbose. Shows various debug messages that are probably only useful
+if you\(aqre hacking on \fBa8xd\fP\&.
 .UNINDENT
 .INDENT 0.0
 .TP
@@ -134,6 +137,9 @@ missing are:
 .IP \(bu 2
 \fB\-b\fP (bits mode).
 .UNINDENT
+.sp
+Another difference is that \fBa8xd\fP doesn\(aqt support files larger than
+2GB. This won\(aqt be a problem for Atari 8\-bit\-related files!
 .SH COPYRIGHT
 .sp
 WTFPL. See \fI\%http://www.wtfpl.net/txt/copying/\fP for details.
diff --git a/a8xd.c b/a8xd.c
index c322624..f051c4b 100644
--- a/a8xd.c
+++ b/a8xd.c
@@ -54,7 +54,6 @@ void parse_seek_arg(const char *arg) {
 
 	if(*arg == '-') {
 		seek_whence = SEEK_END;
-		arg++;
 	}
 
 	seekpos = parse_num_arg(arg);
@@ -64,8 +63,6 @@ int parse_offset_arg(const char *arg) {
 	int got;
 
 	got = parse_num_arg(arg);
-	if(got < 0)
-		die("negative arguments to -o (offset) are not supported.");
 
 	return got;
 }
@@ -84,22 +81,24 @@ FILE *open_input(const char *file) {
 	FILE *input;
 
 	if(file[0] == '-' && file[1] == 0) {
-		if(verbose)
-			fprintf(stderr, "%s: reading from standard input.\n", self);
 		if(freopen(NULL, "rb", stdin)) {
 			input = stdin;
 		} else {
+			fprintf(stderr, "%s: ", self);
 			perror("(standard input)");
 			return NULL;
 		}
-	} else if(!(input = fopen(file, "rb"))) {
-		perror(file);
-		return NULL;
+		if(verbose)
+			fprintf(stderr, "%s: reading from standard input.\n", self);
+	} else {
+		if(!(input = fopen(file, "rb"))) {
+			perror(file);
+			return NULL;
+		}
+		if(verbose)
+			fprintf(stderr, "%s: reading from file '%s'.\n", self, file);
 	}
 
-	if(verbose)
-		fprintf(stderr, "%s: reading from file '%s'.\n", self, file);
-
 	return input;
 }
 
@@ -128,6 +127,44 @@ char *get_color(unsigned char c) {
 	return outbuf;
 }
 
+void fake_seek(FILE *input) {
+	char junkbuf[1024];
+	int pos = 0, chunksize;
+
+	if(verbose)
+		fprintf(stderr, "%s: faking fseek() for stdin, skipping %d bytes.\n", self, seekpos);
+
+	while(pos < seekpos) {
+		chunksize = seekpos - pos;
+		if(chunksize > 1024) chunksize = 1024;
+		if(fread(junkbuf, 1, chunksize, input) != chunksize)
+			die("can't seek past end of input");
+		pos += chunksize;
+	}
+}
+
+void seek_input(FILE *input) {
+	if(verbose)
+		fprintf(stderr, "%s: seeking %d bytes (whence = %d) in input.\n", self, seekpos, seek_whence);
+	if(input == stdin) {
+		/* can't fseek() a stream, fake it */
+		if(seek_whence != SEEK_SET)
+			die("can't seek from the end of standard input.");
+		fake_seek(input);
+	} else {
+		if(fseek(input, seekpos, seek_whence) < 0) {
+			fprintf(stderr, "%s: ", self);
+			perror("fseek() failed");
+			exit(1);
+		}
+		if((filepos = ftell(input)) < 0) {
+			fprintf(stderr, "%s: ", self);
+			perror("ftell() failed");
+			exit(1);
+		}
+	}
+}
+
 void dump_line(const unsigned char *buf, int len) {
 	char hex[1024], asc[1024];
 	int hpos = 0, apos = 0, count = len;
@@ -165,13 +202,17 @@ void dump_line(const unsigned char *buf, int len) {
 
 int a8xd(const char *file) {
 	FILE *input;
-	int c, len = 0;
+	int c, len = 0, count = 0;
 	unsigned char buf[16];
 
 	if( !(input = open_input(file)) )
 		return 1;
 
+	if(seekpos) seek_input(input);
+
 	while( (c = fgetc(input)) != EOF ) {
+		if(limit && (count == limit)) break;
+		count++;
 		if(len && (len % 16 == 0)) {
 			dump_line(buf, len);
 			len = 0;
@@ -181,6 +222,10 @@ int a8xd(const char *file) {
 
 	if(len) dump_line(buf, len);
 
+	if(verbose)
+		fprintf(stderr, "%s: dumped %d (0x%04x) bytes from '%s'.\n", self, count, count, file);
+
+	fclose(input);
 	return 0;
 }
 
@@ -199,7 +244,7 @@ int main(int argc, char **argv) {
 		exit(0);
 	}
 
-	while( (opt = getopt(argc, argv, "vimus:o:l")) != -1) {
+	while( (opt = getopt(argc, argv, "vimus:o:l:")) != -1) {
 		switch(opt) {
 			case 'v': verbose = 1; break;
 			case 'i': table = ics2utf; break;
@@ -207,7 +252,7 @@ int main(int argc, char **argv) {
 			case 'u': word_format = "%04X"; byte_format = "%02X"; break;
 			case 's': parse_seek_arg(optarg); break;
 			case 'o': disp_offset = parse_offset_arg(optarg); break;
-			case 'l': disp_offset = parse_limit_arg(optarg); break;
+			case 'l': limit = parse_limit_arg(optarg); break;
 			default: print_help(); exit(1); break;
 		}
 	}
diff --git a/a8xd.rst b/a8xd.rst
index ebe3364..4803acc 100644
--- a/a8xd.rst
+++ b/a8xd.rst
@@ -47,7 +47,7 @@ Options marked with **\*** are not yet implemented.
   Print XL/XE International Character Set conversions instead of ATASCII.
 
 -l *len*
-  **\*** Stop after dumping *len* bytes. *len* may be given in decimal or hex (with
+  Stop after dumping *len* bytes. *len* may be given in decimal or hex (with
   leading *0x* or *$*).
 
 -m
@@ -56,10 +56,12 @@ Options marked with **\*** are not yet implemented.
 
 -o *offset*
   Add *offset* to displayed file position. *offset* can be given in decimal
-  or hex (with leading *0x* or *$*).
+  or hex (with leading *0x* or *$*). Negative offsets are allowed, but they
+  will be printed as very large positive numbers in the output (this matches
+  **xxd**\'s behaviour).
 
 -s *[-]seek*
-  **\*** Start at *seek* bytes. Without *-*, this is an absolute offset. With *-*,
+  Start at *seek* bytes. Without *-*, this is an absolute offset. With *-*,
   it's relative to the end of the file. The *-* option won't work when
   reading from standard input. *seek* may be given in decimal or hex
   (with leading *0x* or *$*).
@@ -68,7 +70,8 @@ Options marked with **\*** are not yet implemented.
   Use uppercase letters for hex digits; the default is lowercase.
 
 -v
-  Verbose. Currently, this option is accepted, but it doesn't do anything yet.
+  Verbose. Shows various debug messages that are probably only useful
+  if you're hacking on **a8xd**.
 
 **--**
   End of options; the nex argument is the filename. Use this if you're
@@ -100,4 +103,7 @@ missing are:
 
 - **-b** (bits mode).
 
+Another difference is that **a8xd** doesn't support files larger than
+2GB. This won't be a problem for Atari 8-bit-related files!
+
 .. include:: manftr.rst