libs/sig: square wave; sig_ops_sqr / sig_new_sqr()

This builds minimally upon the existing sine wave code,
just use the sign to drive the signal high or low.

Wikipedia shows a third state for 0 values, but that's for a -1..+1
signal.  I'm producing all 0-1 signals as it's more convenient for
this application, but it seems like it would be awkward to return
.5f for the 0 case.  So 0 is being treated as just another positive
value; high.

3 files changed, 45 insertions, 3 deletions

diff --git a/src/libs/sig/ops_sin.c b/src/libs/sig/ops_sin.c
index 555a682..da5b371 100644
--- a/src/libs/sig/ops_sin.c
+++ b/src/libs/sig/ops_sin.c
@@ -35,7 +35,22 @@ static void ops_sin_destroy(void *context)
 }
 
 
-static float ops_sin_output(void *context, unsigned ticks_ms)
+static float output_sin(float rads)
+{
+	return sinf(rads) * .5f + .5f;
+}
+
+
+static float output_sqr(float rads)
+{
+	if (sinf(rads) < 0.f)
+		return 0.f;
+
+	return 1.f;
+}
+
+
+static float output(void *context, unsigned ticks_ms, float (*output_fn)(float rads))
 {
 	ops_sin_ctxt_t	*ctxt = context;
 	float		rads_per_ms, rads, hz;
@@ -56,7 +71,19 @@ static float ops_sin_output(void *context, unsigned ticks_ms)
 	rads_per_ms = (M_PI * 2.f) * hz * .001f;
 	rads = (float)ticks_ms * rads_per_ms;
 
-	return sinf(rads) * .5f + .5f;
+	return output_fn(rads);
+}
+
+
+static float ops_sin_output(void *context, unsigned ticks_ms)
+{
+	return output(context, ticks_ms, output_sin);
+}
+
+
+static float ops_sqr_output(void *context, unsigned ticks_ms)
+{
+	return output(context, ticks_ms, output_sqr);
 }
 
 
@@ -66,3 +93,11 @@ sig_ops_t	sig_ops_sin = {
 	.destroy = ops_sin_destroy,
 	.output = ops_sin_output,
 };
+
+
+sig_ops_t	sig_ops_sqr = {
+	.size = ops_sin_size,
+	.init = ops_sin_init,
+	.destroy = ops_sin_destroy,
+	.output = ops_sqr_output,
+};
diff --git a/src/libs/sig/sig.c b/src/libs/sig/sig.c
index 2c3452c..87a76c4 100644
--- a/src/libs/sig/sig.c
+++ b/src/libs/sig/sig.c
@@ -234,6 +234,12 @@ sig_t * sig_new_sin(sig_t *hz)
 }
 
 
+sig_t * sig_new_sqr(sig_t *hz)
+{
+	return sig_new(&sig_ops_sqr, hz);
+}
+
+
 sig_t * sig_new_sub(sig_t *a, sig_t *b)
 {
 	return sig_new(&sig_ops_sub, a, b);
diff --git a/src/libs/sig/sig.h b/src/libs/sig/sig.h
index e905ba0..917dbc4 100644
--- a/src/libs/sig/sig.h
+++ b/src/libs/sig/sig.h
@@ -37,16 +37,17 @@ sig_t * sig_new_rand(void);
 sig_t * sig_new_round(sig_t *x);
 sig_t * sig_new_scale(sig_t *x, sig_t *min, sig_t *max);
 sig_t * sig_new_sin(sig_t *hz);
+sig_t * sig_new_sqr(sig_t *hz);
 sig_t * sig_new_sub(sig_t *a, sig_t *b);
 
 extern sig_ops_t	sig_ops_const;
 extern sig_ops_t	sig_ops_rand;
 extern sig_ops_t	sig_ops_sin;
+extern sig_ops_t	sig_ops_sqr;
 
 /* TODO:
 extern sig_ops_t	sig_ops_tri;
 extern sig_ops_t	sig_ops_saw;
-extern sig_ops_t	sig_ops_sqr;
 */
 
 extern sig_ops_t	sig_ops_abs;