descriptor: Optimize descriptor parsing

While iterating over descriptors, we can simplify and speed up the
process by looking at the descriptor header directly rather than calling
the parse function each time.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

2 files changed, 61 insertions, 63 deletions

diff --git a/libusb/descriptor.c b/libusb/descriptor.c
index 5124494..d7ec5e2 100644
--- a/libusb/descriptor.c
+++ b/libusb/descriptor.c
@@ -96,7 +96,7 @@ static int parse_endpoint(struct libusb_context *ctx,
 	struct libusb_endpoint_descriptor *endpoint, unsigned char *buffer,
 	int size, int host_endian)
 {
-	struct usbi_descriptor_header header;
+	struct usbi_descriptor_header *header;
 	unsigned char *extra;
 	unsigned char *begin;
 	int parsed = 0;
@@ -108,56 +108,55 @@ static int parse_endpoint(struct libusb_context *ctx,
 		return LIBUSB_ERROR_IO;
 	}
 
-	usbi_parse_descriptor(buffer, "bb", &header, 0);
-	if (header.bDescriptorType != LIBUSB_DT_ENDPOINT) {
+	header = (struct usbi_descriptor_header *)buffer;
+	if (header->bDescriptorType != LIBUSB_DT_ENDPOINT) {
 		usbi_err(ctx, "unexpected descriptor %x (expected %x)",
-			header.bDescriptorType, LIBUSB_DT_ENDPOINT);
+			header->bDescriptorType, LIBUSB_DT_ENDPOINT);
 		return parsed;
-	}
-	if (header.bLength > size) {
+	} else if (header->bLength > size) {
 		usbi_warn(ctx, "short endpoint descriptor read %d/%d",
-			  size, header.bLength);
+			  size, header->bLength);
 		return parsed;
 	}
-	if (header.bLength >= ENDPOINT_AUDIO_DESC_LENGTH)
+	if (header->bLength >= ENDPOINT_AUDIO_DESC_LENGTH)
 		usbi_parse_descriptor(buffer, "bbbbwbbb", endpoint, host_endian);
-	else if (header.bLength >= ENDPOINT_DESC_LENGTH)
+	else if (header->bLength >= ENDPOINT_DESC_LENGTH)
 		usbi_parse_descriptor(buffer, "bbbbwb", endpoint, host_endian);
 	else {
-		usbi_err(ctx, "invalid endpoint bLength (%d)", header.bLength);
+		usbi_err(ctx, "invalid endpoint bLength (%d)", header->bLength);
 		return LIBUSB_ERROR_IO;
 	}
 
-	buffer += header.bLength;
-	size -= header.bLength;
-	parsed += header.bLength;
+	buffer += header->bLength;
+	size -= header->bLength;
+	parsed += header->bLength;
 
 	/* Skip over the rest of the Class Specific or Vendor Specific */
 	/*  descriptors */
 	begin = buffer;
 	while (size >= DESC_HEADER_LENGTH) {
-		usbi_parse_descriptor(buffer, "bb", &header, 0);
-		if (header.bLength < DESC_HEADER_LENGTH) {
+		header = (struct usbi_descriptor_header *)buffer;
+		if (header->bLength < DESC_HEADER_LENGTH) {
 			usbi_err(ctx, "invalid extra ep desc len (%d)",
-				 header.bLength);
+				 header->bLength);
 			return LIBUSB_ERROR_IO;
-		} else if (header.bLength > size) {
+		} else if (header->bLength > size) {
 			usbi_warn(ctx, "short extra ep desc read %d/%d",
-				  size, header.bLength);
+				  size, header->bLength);
 			return parsed;
 		}
 
 		/* If we find another "proper" descriptor then we're done  */
-		if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
-				(header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
-				(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
-				(header.bDescriptorType == LIBUSB_DT_DEVICE))
+		if ((header->bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+				(header->bDescriptorType == LIBUSB_DT_INTERFACE) ||
+				(header->bDescriptorType == LIBUSB_DT_CONFIG) ||
+				(header->bDescriptorType == LIBUSB_DT_DEVICE))
 			break;
 
-		usbi_dbg("skipping descriptor %x", header.bDescriptorType);
-		buffer += header.bLength;
-		size -= header.bLength;
-		parsed += header.bLength;
+		usbi_dbg("skipping descriptor %x", header->bDescriptorType);
+		buffer += header->bLength;
+		size -= header->bLength;
+		parsed += header->bLength;
 	}
 
 	/* Copy any unknown descriptors into a storage area for drivers */
@@ -214,7 +213,7 @@ static int parse_interface(libusb_context *ctx,
 	int r;
 	int parsed = 0;
 	int interface_number = -1;
-	struct usbi_descriptor_header header;
+	struct usbi_descriptor_header *header;
 	struct libusb_interface_descriptor *ifp;
 	unsigned char *begin;
 
@@ -273,30 +272,30 @@ static int parse_interface(libusb_context *ctx,
 
 		/* Skip over any interface, class or vendor descriptors */
 		while (size >= DESC_HEADER_LENGTH) {
-			usbi_parse_descriptor(buffer, "bb", &header, 0);
-			if (header.bLength < DESC_HEADER_LENGTH) {
+			header = (struct usbi_descriptor_header *)buffer;
+			if (header->bLength < DESC_HEADER_LENGTH) {
 				usbi_err(ctx,
 					 "invalid extra intf desc len (%d)",
-					 header.bLength);
+					 header->bLength);
 				r = LIBUSB_ERROR_IO;
 				goto err;
-			} else if (header.bLength > size) {
+			} else if (header->bLength > size) {
 				usbi_warn(ctx,
 					  "short extra intf desc read %d/%d",
-					  size, header.bLength);
+					  size, header->bLength);
 				return parsed;
 			}
 
 			/* If we find another "proper" descriptor then we're done */
-			if ((header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
-					(header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
-					(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
-					(header.bDescriptorType == LIBUSB_DT_DEVICE))
+			if ((header->bDescriptorType == LIBUSB_DT_INTERFACE) ||
+					(header->bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+					(header->bDescriptorType == LIBUSB_DT_CONFIG) ||
+					(header->bDescriptorType == LIBUSB_DT_DEVICE))
 				break;
 
-			buffer += header.bLength;
-			parsed += header.bLength;
-			size -= header.bLength;
+			buffer += header->bLength;
+			parsed += header->bLength;
+			size -= header->bLength;
 		}
 
 		/* Copy any unknown descriptors into a storage area for */
@@ -369,7 +368,7 @@ static int parse_configuration(struct libusb_context *ctx,
 {
 	int i;
 	int r;
-	struct usbi_descriptor_header header;
+	struct usbi_descriptor_header *header;
 	struct libusb_interface *usb_interface;
 
 	if (size < LIBUSB_DT_CONFIG_SIZE) {
@@ -417,32 +416,31 @@ static int parse_configuration(struct libusb_context *ctx,
 		/*  Specific descriptors */
 		begin = buffer;
 		while (size >= DESC_HEADER_LENGTH) {
-			usbi_parse_descriptor(buffer, "bb", &header, 0);
-
-			if (header.bLength < DESC_HEADER_LENGTH) {
+			header = (struct usbi_descriptor_header *)buffer;
+			if (header->bLength < DESC_HEADER_LENGTH) {
 				usbi_err(ctx,
 					 "invalid extra config desc len (%d)",
-					 header.bLength);
+					 header->bLength);
 				r = LIBUSB_ERROR_IO;
 				goto err;
-			} else if (header.bLength > size) {
+			} else if (header->bLength > size) {
 				usbi_warn(ctx,
 					  "short extra config desc read %d/%d",
-					  size, header.bLength);
+					  size, header->bLength);
 				config->bNumInterfaces = (uint8_t)i;
 				return size;
 			}
 
 			/* If we find another "proper" descriptor then we're done */
-			if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
-					(header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
-					(header.bDescriptorType == LIBUSB_DT_CONFIG) ||
-					(header.bDescriptorType == LIBUSB_DT_DEVICE))
+			if ((header->bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+					(header->bDescriptorType == LIBUSB_DT_INTERFACE) ||
+					(header->bDescriptorType == LIBUSB_DT_CONFIG) ||
+					(header->bDescriptorType == LIBUSB_DT_DEVICE))
 				break;
 
-			usbi_dbg("skipping descriptor 0x%x", header.bDescriptorType);
-			buffer += header.bLength;
-			size -= header.bLength;
+			usbi_dbg("skipping descriptor 0x%x", header->bDescriptorType);
+			buffer += header->bLength;
+			size -= header->bLength;
 		}
 
 		/* Copy any unknown descriptors into a storage area for */
@@ -750,27 +748,27 @@ int API_EXPORTED libusb_get_ss_endpoint_companion_descriptor(
 	const struct libusb_endpoint_descriptor *endpoint,
 	struct libusb_ss_endpoint_companion_descriptor **ep_comp)
 {
-	struct usbi_descriptor_header header;
+	struct usbi_descriptor_header *header;
 	int size = endpoint->extra_length;
 	const unsigned char *buffer = endpoint->extra;
 
 	*ep_comp = NULL;
 
 	while (size >= DESC_HEADER_LENGTH) {
-		usbi_parse_descriptor(buffer, "bb", &header, 0);
-		if (header.bLength < 2 || header.bLength > size) {
+		header = (struct usbi_descriptor_header *)buffer;
+		if (header->bLength < 2 || header->bLength > size) {
 			usbi_err(ctx, "invalid descriptor length %d",
-				 header.bLength);
+				 header->bLength);
 			return LIBUSB_ERROR_IO;
 		}
-		if (header.bDescriptorType != LIBUSB_DT_SS_ENDPOINT_COMPANION) {
-			buffer += header.bLength;
-			size -= header.bLength;
+		if (header->bDescriptorType != LIBUSB_DT_SS_ENDPOINT_COMPANION) {
+			buffer += header->bLength;
+			size -= header->bLength;
 			continue;
 		}
-		if (header.bLength < LIBUSB_DT_SS_ENDPOINT_COMPANION_SIZE) {
+		if (header->bLength < LIBUSB_DT_SS_ENDPOINT_COMPANION_SIZE) {
 			usbi_err(ctx, "invalid ss-ep-comp-desc length %d",
-				 header.bLength);
+				 header->bLength);
 			return LIBUSB_ERROR_IO;
 		}
 		*ep_comp = malloc(sizeof(**ep_comp));
diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index a2f78dc..2aa9119 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 11502
+#define LIBUSB_NANO 11503