libs/sig: add sig_ops_expand convenience

This is a specialized version of sig_ops_scale which assumes a
min..max range of -1..+1

nvidia register combiners docs describe this operation as "expand
normal", and they have several variants, but I don't want to go
too crazy here right now.  Plain expand it is.

3 files changed, 58 insertions, 1 deletions

diff --git a/src/libs/sig/Makefile.am b/src/libs/sig/Makefile.am
index e53a4bd..8ee3dbe 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_abs.c ops_ceil.c ops_clamp.c ops_const.c ops_floor.c ops_inv.c ops_lerp.c ops_max.c ops_min.c ops_mult.c ops_pow.c ops_rand.c ops_round.c ops_scale.c ops_sin.c sig.c sig.h
+libsig_a_SOURCES = ops_abs.c ops_ceil.c ops_clamp.c ops_const.c ops_expand.c ops_floor.c ops_inv.c ops_lerp.c ops_max.c ops_min.c ops_mult.c ops_pow.c ops_rand.c ops_round.c ops_scale.c ops_sin.c sig.c sig.h
 libsig_a_CPPFLAGS = -I@top_srcdir@/src
diff --git a/src/libs/sig/ops_expand.c b/src/libs/sig/ops_expand.c
new file mode 100644
index 0000000..76791e4
--- /dev/null
+++ b/src/libs/sig/ops_expand.c
@@ -0,0 +1,56 @@
+#include <assert.h>
+
+#include "sig.h"
+
+
+typedef struct ops_expand_ctxt_t {
+	sig_t	*value;
+} ops_expand_ctxt_t;
+
+
+static size_t ops_expand_size(va_list ap)
+{
+	return sizeof(ops_expand_ctxt_t);
+}
+
+
+/* expects a single sig_t: value
+ * input range is assumed to be 0..1, outputs expanded
+ * range of -1..+1
+ */
+static void ops_expand_init(void *context, va_list ap)
+{
+	ops_expand_ctxt_t	*ctxt = context;
+
+	assert(ctxt);
+
+	ctxt->value = va_arg(ap, sig_t *);
+}
+
+
+static void ops_expand_destroy(void *context)
+{
+	ops_expand_ctxt_t	*ctxt = context;
+
+	assert(ctxt);
+
+	sig_free(ctxt->value);
+}
+
+
+static float ops_expand_output(void *context, unsigned ticks_ms)
+{
+	ops_expand_ctxt_t	*ctxt = context;
+
+	assert(ctxt);
+
+	return sig_output(ctxt->value, ticks_ms) * 2.f + 1.f;
+}
+
+
+sig_ops_t	sig_ops_expand = {
+	.size = ops_expand_size,
+	.init = ops_expand_init,
+	.destroy = ops_expand_destroy,
+	.output = ops_expand_output,
+};
diff --git a/src/libs/sig/sig.h b/src/libs/sig/sig.h
index b54bfb7..f6cb189 100644
--- a/src/libs/sig/sig.h
+++ b/src/libs/sig/sig.h
@@ -30,6 +30,7 @@ extern sig_ops_t	sig_ops_sqr;
 extern sig_ops_t	sig_ops_abs;
 extern sig_ops_t	sig_ops_ceil;
 extern sig_ops_t	sig_ops_clamp;
+extern sig_ops_t	sig_ops_expand;
 extern sig_ops_t	sig_ops_floor;
 extern sig_ops_t	sig_ops_inv;
 extern sig_ops_t	sig_ops_lerp;