blind

commit 85e42eb61c6d87215e9c1cc994668e58d57089c0
parent 9783831e37ca5718e20259be70c23e229d3583c4
Author: Mattias Andrée <maandree@kth.se>
Date:   Sat, 14 Jan 2017 10:39:12 +0100

blind-reverse: add -i (reverse file in place)

Signed-off-by: Mattias Andrée <maandree@kth.se>

Diffstat:
M
src/blind-reverse.c
 | 
106
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------------

1 file changed, 83 insertions(+), 23 deletions(-)
diff --git a/src/blind-reverse.c b/src/blind-reverse.c
@@ -5,46 +5,106 @@
 #include <limits.h>
 #include <unistd.h>
 
-USAGE("file")
+USAGE("[-i] file")
+
+static void
+to_stdout(struct stream *stream, size_t frame_size)
+{
+	size_t ptr, end, n;
+	char buf[BUFSIZ];
+	ssize_t r;
+
+	while (stream->frames--) {
+		ptr = stream->frames * frame_size + stream->headlen;
+		end = ptr + frame_size;
+		while (ptr < end) {
+			r = pread(stream->fd, buf, sizeof(buf), ptr);
+			if (r < 0)
+				eprintf("pread %s:", stream->file);
+			else if (r == 0)
+				eprintf("%s: file is shorter than expected\n", stream->file);
+			ptr += n = (size_t)r;
+			ewriteall(STDOUT_FILENO, buf, n, "<stdout>");
+		}
+	}
+}
+
+static void
+elseek_set(int fd, off_t offset, const char *fname)
+{
+	off_t r = lseek(fd, offset, SEEK_SET);
+	if (r < 0)
+		eprintf("lseek %s:", fname);
+	if (r != offset)
+		eprintf("%s: file is shorter than expected\n", fname);
+}
+
+static void
+in_place(struct stream *stream, size_t frame_size)
+{
+	size_t f, fm = stream->frames - 1;
+	off_t pa, pb;
+	char *bufa, *bufb;
+
+	bufa = emalloc(frame_size);
+	bufb = emalloc(frame_size);
+
+	for (f = 0; f < stream->frames >> 1; f++) {
+		pa = f        * frame_size + stream->headlen;
+		pb = (fm - f) * frame_size + stream->headlen;
+		eread_frame(stream, bufa, frame_size);
+		elseek_set(stream->fd, pb, stream->file);
+		eread_frame(stream, bufb, frame_size);
+		elseek_set(stream->fd, pb, stream->file);
+		ewriteall(stream->fd, bufa, frame_size, stream->file);
+		elseek_set(stream->fd, pa, stream->file);
+		ewriteall(stream->fd, bufb, frame_size, stream->file);
+	}
+
+	free(bufa);
+	free(bufb);
+}
 
 int
 main(int argc, char *argv[])
 {
 	struct stream stream;
-	size_t frame_size, ptr, end, n;
-	ssize_t r;
-	char buf[BUFSIZ];
+	size_t frame_size;
+	int inplace = 0;
 
-	ENOFLAGS(argc != 1);
+	ARGBEGIN {
+	case 'i':
+		inplace = 1;
+		break;
+	default:
+		usage();
+	} ARGEND;
+	
+	if (argc != 1)
+		usage();
 
 	stream.file = argv[0];
-	stream.fd = eopen(stream.file, O_RDONLY);
+	stream.fd = eopen(stream.file, inplace ? O_RDWR : O_RDONLY);
 	einit_stream(&stream);
-	fprint_stream_head(stdout, &stream);
-	efflush(stdout, "<stdout>");
+	if (!inplace) {
+		fprint_stream_head(stdout, &stream);
+		efflush(stdout, "<stdout>");
+	}
 	echeck_frame_size(stream.width, stream.height, stream.pixel_size, 0, stream.file);
 	frame_size = stream.width * stream.height * stream.pixel_size;
-	if (stream.frames > SSIZE_MAX / frame_size)
+	if (stream.frames > (size_t)SSIZE_MAX / frame_size)
 		eprintf("%s: video is too large\n", stream.file);
-	if (stream.frames * frame_size > SSIZE_MAX - stream.headlen)
+	if (stream.frames * frame_size > (size_t)SSIZE_MAX - stream.headlen)
 		eprintf("%s: video is too large\n", stream.file);
 
 #if defined(POSIX_FADV_RANDOM)
 	posix_fadvise(stream.fd, 0, 0, POSIX_FADV_RANDOM);
 #endif
-	while (stream.frames--) {
-		ptr = stream.frames * frame_size + stream.headlen;
-		end = ptr + frame_size;
-		while (ptr < end) {
-			r = pread(stream.fd, buf, sizeof(buf), ptr);
-			if (r < 0)
-				eprintf("pread %s:", stream.file);
-			else if (r == 0)
-				eprintf("%s: file is shorter than expected\n", stream.file);
-			ptr += n = (size_t)r;
-			ewriteall(STDOUT_FILENO, buf, n, "<stdout>");
-		}
-	}
+
+	if (inplace)
+		in_place(&stream, frame_size);
+	else
+		to_stdout(&stream, frame_size);
 
 	close(stream.fd);
 	return 0;