libs/sig: add sig_ops_rand random generator

(Ab)uses rand_r by feeding ticks_ms as seedp for pseudo-random
numbers deterministically derived from ticks_ms.

4 files changed, 24 insertions, 1 deletions

diff --git a/src/libs/sig/Makefile.am b/src/libs/sig/Makefile.am
index 7c35742..55032b4 100644
--- a/src/libs/sig/Makefile.am
+++ b/src/libs/sig/Makefile.am
@@ -1,3 +1,3 @@
 noinst_LIBRARIES = libsig.a
-libsig_a_SOURCES = ops_const.c ops_lerp.c ops_mult.c ops_sin.c sig.c sig.h
+libsig_a_SOURCES = ops_const.c ops_lerp.c ops_mult.c ops_rand.c ops_sin.c sig.c sig.h
 libsig_a_CPPFLAGS = -I@top_srcdir@/src
diff --git a/src/libs/sig/ops_rand.c b/src/libs/sig/ops_rand.c
new file mode 100644
index 0000000..49954c6
--- /dev/null
+++ b/src/libs/sig/ops_rand.c
@@ -0,0 +1,16 @@
+#include <assert.h>
+#include <stdlib.h>
+
+#include "sig.h"
+
+
+static float ops_rand_output(void *context, unsigned ticks_ms)
+{
+	return rand_r(&ticks_ms) * 1.f / (float)RAND_MAX;
+}
+
+
+sig_ops_t	sig_ops_rand = {
+	.output = ops_rand_output,
+};
+
diff --git a/src/libs/sig/sig.c b/src/libs/sig/sig.c
index cd179e2..fea83b6 100644
--- a/src/libs/sig/sig.c
+++ b/src/libs/sig/sig.c
@@ -83,6 +83,12 @@ int main(int argc, char *argv[])
 	printf("null output=%f\n", sig_output(sig, 0));
 	sig = sig_free(sig);
 
+	sig = sig_new(&sig_ops_rand);
+	for (unsigned j = 0; j < 2; j++) {
+		for (unsigned i = 0; i < 10; i++)
+			printf("rand j=%u i=%u output=%f\n", j, i, sig_output(sig, i));
+	}
+
 	sig = sig_new(&sig_ops_sin, sig_new(&sig_ops_const, 2.f));
 	for (unsigned i = 0; i < 1000; i++)
 		printf("sin 2hz output %i=%f\n", i, sig_output(sig, i));
diff --git a/src/libs/sig/sig.h b/src/libs/sig/sig.h
index 0a374f5..32bf446 100644
--- a/src/libs/sig/sig.h
+++ b/src/libs/sig/sig.h
@@ -18,6 +18,7 @@ sig_t * sig_free(sig_t *sig);
 float sig_output(sig_t *sig, unsigned ticks_ms);
 
 extern sig_ops_t	sig_ops_const;
+extern sig_ops_t	sig_ops_rand;
 extern sig_ops_t	sig_ops_sin;
 
 /* TODO: