From: Gerhard Sittig <redacted>
Date: Mon, 31 Jan 2022 21:08:41 +0000 (+0100)
Subject: kingst-la2016: rephrase USB bulk transfer size padding constraint
X-Git-Url: https://sigrok.org/gitaction?a=commitdiff_plain;h=418dfd7ed3bb2c62c110f7924c796e126fd41e79;p=libsigrok.git

kingst-la2016: rephrase USB bulk transfer size padding constraint

Always round up capture data USB bulk transfer sizes to full EP 6 packet
sizes. The previous implementation suggested that it's only required for
smaller transfers, but it's just a coincidence that the upper limit of
256KiB happened to also be a multiple of the 512B packet size.

It's assumed that capping at the absolute size limit and always padding
is more readable and as reliable as the previous if-else logic was.

Rephrase the round up by means of integer multiplication instead of
bit twiddling. Compilers should get what is intended, humans may prefer
to read the former.
---

diff --git a/src/hardware/kingst-la2016/protocol.c b/src/hardware/kingst-la2016/protocol.c
index a92c822a..6ab72df0 100644
--- a/src/hardware/kingst-la2016/protocol.c
+++ b/src/hardware/kingst-la2016/protocol.c
@@ -1018,8 +1018,9 @@ static int la2016_start_download(const struct sr_dev_inst *sdi,
 	to_read = devc->n_bytes_to_read;
 	if (to_read >= LA2016_USB_BUFSZ) /* Multiple transfers. */
 		to_read = LA2016_USB_BUFSZ;
-	else /* One transfer. */
-		to_read = (to_read + (LA2016_EP6_PKTSZ-1)) & ~(LA2016_EP6_PKTSZ-1);
+	to_read += LA2016_EP6_PKTSZ - 1;
+	to_read /= LA2016_EP6_PKTSZ;
+	to_read *= LA2016_EP6_PKTSZ;
 	buffer = g_try_malloc(to_read);
 	if (!buffer) {
 		sr_dbg("USB bulk transfer size %d bytes.", (int)to_read);
@@ -1144,8 +1145,9 @@ static void LIBUSB_CALL receive_transfer(struct libusb_transfer *transfer)
 		 */
 		if (to_read >= LA2016_USB_BUFSZ)
 			to_read = LA2016_USB_BUFSZ;
-		else
-			to_read = (to_read + (LA2016_EP6_PKTSZ-1)) & ~(LA2016_EP6_PKTSZ-1);
+		to_read += LA2016_EP6_PKTSZ - 1;
+		to_read /= LA2016_EP6_PKTSZ;
+		to_read *= LA2016_EP6_PKTSZ;
 		libusb_fill_bulk_transfer(transfer,
 			usb->devhdl, USB_EP_CAPTURE_DATA | LIBUSB_ENDPOINT_IN,
 			transfer->buffer, to_read,