util/spkmodem-recv: further portability / cleanup

i used a bunch of global variables. that's gone.

added proper externs, including for errno. lots of
old unix systems require this. this version should
be perfectly polished and portable now.

all status is now handled in a struct, making the
code a bit easier to understand, because the variables
now are clearly pertinent to the state of the decoder,
rather than being seemingly random.

some indentation reduced.

also cleaned up ftell/feof usage again. the new code
is a bit more robust when dealing with piped input(which
is literally what this program takes, exclusively)

i started my cleanup of this tool from GNU GRUB in 2023.

i finished it today.

also the Openbsd pledge is more portable now (code made
to compile on pre-pledge openbsd as well)

Signed-off-by: Leah Rowe <leah@libreboot.org>

1 files changed, 127 insertions, 97 deletions

diff --git a/util/spkmodem_recv/spkmodem-recv.c b/util/spkmodem_recv/spkmodem-recv.c
index 7183563b..504121ab 100644
--- a/util/spkmodem_recv/spkmodem-recv.c
+++ b/util/spkmodem_recv/spkmodem-recv.c
@@ -9,6 +9,10 @@
 
 #define _POSIX_SOURCE
 
+/*
+ * For OpenBSD define, to detect version
+ * for deciding whether to use pledge(2)
+ */
 #ifdef __OpenBSD__
 #include <sys/param.h>
 #endif
@@ -20,179 +24,216 @@
 #include <string.h>
 #include <unistd.h>
 
-static int set_ascii_bit(void);
-static void handle_audio(void), decode_pulse(void), print_char(void),
-    print_stats(void);
-static void err(int nvm_errval, const char *msg, ...);
-static const char * getnvmprogname(void);
-static void set_err_if_unset(int x);
-
-int getopt(int, char * const *, const char *);
-extern char *optarg;
-extern int optind, opterr, optopt;
-
-#if defined(__OpenBSD__) && defined(OpenBSD)
-#if OpenBSD >= 509
-#ifndef HAVE_PLEDGE
-#define HAVE_PLEDGE 1
-#endif
-#endif
-#endif
-
 #define SAMPLES_PER_FRAME 240
 #define MAX_SAMPLES (2 * SAMPLES_PER_FRAME)
+
 #define FREQ_SEP_MIN 5
 #define FREQ_SEP_MAX 15
+
 #define FREQ_DATA_MIN 15
 #define FREQ_DATA_THRESHOLD 25
 #define FREQ_DATA_MAX 60
+
 #define THRESHOLD 500
 
-#define reset_char() ascii = 0, ascii_bit = 7
+struct decoder_state {
+	signed short frame[MAX_SAMPLES];
+	unsigned char pulse[MAX_SAMPLES];
+
+	int ringpos;
+	int freq_data;
+	int freq_separator;
+	int sample_count;
+
+	int ascii_bit;
+	unsigned char ascii;
 
-signed short frame[MAX_SAMPLES], pulse[MAX_SAMPLES];
-int ringpos, debug, freq_data, freq_separator, sample_count, ascii_bit = 7;
-char ascii = 0;
+	int debug;
+};
 
 static const char *argv0;
 
+static void handle_audio(struct decoder_state *st);
+static void decode_pulse(struct decoder_state *st);
+static int set_ascii_bit(struct decoder_state *st);
+static void print_char(struct decoder_state *st);
+static void print_stats(struct decoder_state *st);
+static void reset_char(struct decoder_state *st);
+
+static void err(int errval, const char *msg, ...);
+static const char *progname(void);
+
+int getopt(int, char * const *, const char *);
+extern char *optarg;
+extern int optind;
+extern int opterr;
+extern int optopt;
+
+#ifndef errno
+extern int errno;
+#endif
+
 int
-main(int argc, char *argv[])
+main(int argc, char **argv)
 {
-	int c = 0;
-
-	argv0 = argv[0];
+	struct decoder_state st;
+	int c;
 
-#ifdef HAVE_PLEDGE
-#if HAVE_PLEDGE > 0
+#if defined (__OpenBSD__) && defined(OpenBSD)
+#if OpenBSD >= 509
 	if (pledge("stdio", NULL) == -1)
 		err(errno, "pledge");
 #endif
 #endif
-	while (c != -1) {
+
+	memset(&st, 0, sizeof(st));
+	st.ascii_bit = 7;
+
+	argv0 = argv[0];
+
+	while (1) {
 		c = getopt(argc, argv, "d");
+		if (c == -1)
+			break;
 
 		if (c == 'd')
-			debug = 1;
-		else if (c != -1)
+			st.debug = 1;
+		else
 			err(EINVAL, "Invalid argument");
 	}
 
 	setvbuf(stdout, NULL, _IONBF, 0);
 
-	while (1)
-		handle_audio();
+	for (;;)
+		handle_audio(&st);
 
 	return EXIT_SUCCESS;
 }
 
 static void
-handle_audio(void)
+handle_audio(struct decoder_state *st)
 {
 	int sample;
 
-	if (sample_count > (3 * SAMPLES_PER_FRAME))
-		sample_count = reset_char();
+	if (st->sample_count > (3 * SAMPLES_PER_FRAME))
+		reset_char(st);
 
-	if ((freq_separator <= FREQ_SEP_MIN) || (freq_separator >= FREQ_SEP_MAX)
-	    || (freq_data <= FREQ_DATA_MIN) || (freq_data >= FREQ_DATA_MAX)) {
-		decode_pulse();
+	if ((st->freq_separator <= FREQ_SEP_MIN) ||
+	    (st->freq_separator >= FREQ_SEP_MAX) ||
+	    (st->freq_data <= FREQ_DATA_MIN) ||
+	    (st->freq_data >= FREQ_DATA_MAX)) {
+
+		decode_pulse(st);
 		return;
 	}
 
-	if (set_ascii_bit() < 0)
-		print_char();
+	if (set_ascii_bit(st) < 0)
+		print_char(st);
 
-	sample_count = 0;
+	st->sample_count = 0;
 
 	for (sample = 0; sample < SAMPLES_PER_FRAME; sample++)
-		decode_pulse();
+		decode_pulse(st);
 }
 
 static void
-decode_pulse(void)
+decode_pulse(struct decoder_state *st)
 {
 	size_t n;
-	int next_ringpos;
+	int next;
 
-	next_ringpos = (ringpos + SAMPLES_PER_FRAME) % MAX_SAMPLES;
+	next = (st->ringpos + SAMPLES_PER_FRAME) % MAX_SAMPLES;
 
-	freq_data -= pulse[ringpos];
-	freq_data += pulse[next_ringpos];
-	freq_separator -= pulse[next_ringpos];
+	st->freq_data -= st->pulse[st->ringpos];
+	st->freq_data += st->pulse[next];
+	st->freq_separator -= st->pulse[next];
 
-	n = fread(&frame[ringpos], 1, sizeof(frame[0]), stdin);
-	if (n != sizeof(frame[0])) {
+	n = fread(&st->frame[st->ringpos], sizeof(st->frame[0]), 1, stdin);
+	if (n != 1) {
 		if (feof(stdin))
 			exit(EXIT_SUCCESS);
 		err(errno, "stdin read");
 	}
 
-	pulse[ringpos] = (abs(frame[ringpos]) > THRESHOLD) ? 1 : 0;
+	if (abs(st->frame[st->ringpos]) > THRESHOLD)
+		st->pulse[st->ringpos] = 1;
+	else
+		st->pulse[st->ringpos] = 0;
 
-	freq_separator += pulse[ringpos];
-	ringpos = (ringpos + 1) % MAX_SAMPLES;
+	st->freq_separator += st->pulse[st->ringpos];
 
-	++sample_count;
+	st->ringpos = (st->ringpos + 1) % MAX_SAMPLES;
+	st->sample_count++;
 }
 
 static int
-set_ascii_bit(void)
+set_ascii_bit(struct decoder_state *st)
 {
-	if (debug)
-		print_stats();
+	if (st->debug)
+		print_stats(st);
+
+	if (st->freq_data < FREQ_DATA_THRESHOLD)
+		st->ascii |= (1 << st->ascii_bit);
 
-	if (freq_data < FREQ_DATA_THRESHOLD)
-		ascii |= (1 << ascii_bit);
+	st->ascii_bit--;
 
-	--ascii_bit;
-	return ascii_bit;
+	return st->ascii_bit;
 }
 
 static void
-print_stats(void)
+print_char(struct decoder_state *st)
 {
-	long stdin_pos;
-
-	if ((stdin_pos = ftell(stdin)) == -1)
-		err(errno, "ftell stdin");
+	if (st->debug)
+		printf("<%c,%x>", st->ascii, st->ascii);
+	else
+		putchar(st->ascii);
 
-	printf ("%d %d %d @%ld\n", freq_data, freq_separator,
-	    FREQ_DATA_THRESHOLD, stdin_pos - sizeof(frame));
+	reset_char(st);
 }
 
 static void
-print_char(void)
+print_stats(struct decoder_state *st)
 {
-	if (debug)
-		printf("<%c, %x>", ascii, ascii);
-	else
-		printf("%c", ascii);
+	long pos;
+
+	pos = ftell(stdin);
+	if (pos == -1)
+		err(errno, "ftell");
 
-	reset_char();
+	printf("%d %d %d @%ld\n",
+	    st->freq_data,
+	    st->freq_separator,
+	    FREQ_DATA_THRESHOLD,
+	    pos - sizeof(st->frame));
 }
 
 static void
-err(int nvm_errval, const char *msg, ...)
+reset_char(struct decoder_state *st)
 {
-	va_list args;
+	st->ascii = 0;
+	st->ascii_bit = 7;
+}
 
-	fprintf(stderr, "%s: ", getnvmprogname());
+static void
+err(int errval, const char *msg, ...)
+{
+	va_list ap;
 
-	va_start(args, msg);
-	vfprintf(stderr, msg, args);
-	va_end(args);
+	fprintf(stderr, "%s: ", progname());
 
-	set_err_if_unset(nvm_errval);
-	fprintf(stderr, ": %s", strerror(errno));
+	va_start(ap, msg);
+	vfprintf(stderr, msg, ap);
+	va_end(ap);
 
-	fprintf(stderr, "\n");
+	if (!errno)
+		errno = errval;
 
+	fprintf(stderr, ": %s\n", strerror(errno));
 	exit(EXIT_FAILURE);
 }
 
 static const char *
-getnvmprogname(void)
+progname(void)
 {
 	const char *p;
 
@@ -206,14 +247,3 @@ getnvmprogname(void)
 	else
 		return argv0;
 }
-
-static void
-set_err_if_unset(int x)
-{
-	if (errno)
-		return;
-	if (x > 0)
-		errno = x;
-	else
-		errno = ECANCELED;
-}