transform: Add an "invert" transform module.

This inverts the data values:

 - An analog value of x becomes 1/x.

 - A digital value of 0 becomes 1 (and vice versa).

Makefile.am

@@ -72,7 +72,8 @@ libsigrok_la_SOURCES += \
 libsigrok_la_SOURCES += \
 	src/transform/transform.c \
 	src/transform/nop.c \
-	src/transform/scale.c
+	src/transform/scale.c \
+	src/transform/invert.c
 
 # SCPI support
 libsigrok_la_SOURCES += \

src/transform/invert.c

@@ -0,0 +1,87 @@
+/*
+ * This file is part of the libsigrok project.
+ *
+ * Copyright (C) 2015 Uwe Hermann <uwe@hermann-uwe.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+#include <string.h>
+#include "libsigrok.h"
+#include "libsigrok-internal.h"
+
+#define LOG_PREFIX "transform/invert"
+
+static int receive(const struct sr_transform *t,
+		struct sr_datafeed_packet *packet_in,
+		struct sr_datafeed_packet **packet_out)
+{
+	const struct sr_datafeed_logic *logic;
+	const struct sr_datafeed_analog *analog;
+	struct sr_channel *ch;
+	GSList *l;
+	float *fdata, *f;
+	int si, num_channels, c;
+	uint8_t *b;
+	uint64_t i, j;
+
+	if (!t || !t->sdi || !packet_in || !packet_out)
+		return SR_ERR_ARG;
+
+	switch (packet_in->type) {
+	case SR_DF_LOGIC:
+		logic = packet_in->payload;
+		for (i = 0; i <= logic->length - logic->unitsize; i += logic->unitsize) {
+			for (j = 0; j < logic->unitsize; j++) {
+				/* For now invert every bit in every byte. */
+				b = (uint8_t *)logic->data + i + logic->unitsize - 1 - j;
+				*b = ~(*b);
+			}
+		}
+		break;
+	case SR_DF_ANALOG:
+		analog = packet_in->payload;
+		fdata = (float *)analog->data;
+		num_channels = g_slist_length(analog->channels);
+		for (si = 0; si < analog->num_samples; si++) {
+			/* For now invert all values in all channels. */
+			for (l = analog->channels, c = 0; l; l = l->next, c++) {
+				ch = l->data;
+				(void)ch;
+				f = &fdata[si * num_channels + c];
+				*f = 1.0 / *f;
+			}
+		}
+		break;
+	default:
+		sr_spew("Unsupported packet type %d, ignoring.", packet_in->type);
+		break;
+	}
+
+	/* Return the in-place-modified packet. */
+	*packet_out = packet_in;
+
+	return SR_OK;
+}
+
+SR_PRIV struct sr_transform_module transform_invert = {
+	.id = "invert",
+	.name = "Invert",
+	.desc = "Invert values",
+	.options = NULL,
+	.init = NULL,
+	.receive = receive,
+	.cleanup = NULL,
+};

src/transform/transform.c

@@ -41,11 +41,13 @@
 /** @cond PRIVATE */
 extern SR_PRIV struct sr_transform_module transform_nop;
 extern SR_PRIV struct sr_transform_module transform_scale;
+extern SR_PRIV struct sr_transform_module transform_invert;
 /* @endcond */
 
 static const struct sr_transform_module *transform_module_list[] = {
 	&transform_nop,
 	&transform_scale,
+	&transform_invert,
 	NULL,
 };