HID: simplify implement() a bit

The 'size' variable is not really needed, and we can also shift constant
in the loop body when masking off existing bits.

Also we do not have to use 64 bit calculations if we take an extra
branch.

[jkosina@suse.cz: fix a small error in changelog]
Suggested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -1129,49 +1129,46 @@ EXPORT_SYMBOL_GPL(hid_field_extract);
 static void __implement(u8 *report, unsigned offset, int n, u32 value)
 {
 	unsigned int idx = offset / 8;
-	unsigned int size = offset + n;
 	unsigned int bit_shift = offset % 8;
 	int bits_to_set = 8 - bit_shift;
-	u8 bit_mask = 0xff << bit_shift;
 
 	while (n - bits_to_set >= 0) {
-		report[idx] &= ~bit_mask;
+		report[idx] &= ~(0xff << bit_shift);
 		report[idx] |= value << bit_shift;
 		value >>= bits_to_set;
 		n -= bits_to_set;
 		bits_to_set = 8;
-		bit_mask = 0xff;
 		bit_shift = 0;
 		idx++;
 	}
 
 	/* last nibble */
 	if (n) {
-		if (size % 8)
-			bit_mask &= (1U << (size % 8)) - 1;
-		report[idx] &= ~bit_mask;
-		report[idx] |= (value << bit_shift) & bit_mask;
+		u8 bit_mask = ((1U << n) - 1);
+		report[idx] &= ~(bit_mask << bit_shift);
+		report[idx] |= value << bit_shift;
 	}
 }
 
 static void implement(const struct hid_device *hid, u8 *report,
 		      unsigned offset, unsigned n, u32 value)
 {
-	u64 m;
-
-	if (n > 32) {
+	if (unlikely(n > 32)) {
 		hid_warn(hid, "%s() called with n (%d) > 32! (%s)\n",
 			 __func__, n, current->comm);
 		n = 32;
+	} else if (n < 32) {
+		u32 m = (1U << n) - 1;
+
+		if (unlikely(value > m)) {
+			hid_warn(hid,
+				 "%s() called with too large value %d (n: %d)! (%s)\n",
+				 __func__, value, n, current->comm);
+			WARN_ON(1);
+			value &= m;
+		}
 	}
 
-	m = (1ULL << n) - 1;
-	if (value > m)
-		hid_warn(hid, "%s() called with too large value %d! (%s)\n",
-			 __func__, value, current->comm);
-	WARN_ON(value > m);
-	value &= m;
-
 	__implement(report, offset, n, value);
 }