--- linux-2.4.1/drivers/acpi/interpreter/amfldio.c	Mon Jan 29 10:15:59 2001
+++ linux/drivers/acpi/interpreter/amfldio.c	Wed Jan 31 05:23:48 2001
@@ -415,7 +415,8 @@
 
 		/* Check if update rule needs to be applied (not if mask is all ones) */
 
-		if (((1 << bit_granularity) -1) & ~mask) {
+		/* The left shift drops the bits we want to ignore. */
+	  	if ((~mask << (sizeof(mask)*8 - bit_granularity)) != 0) {
 			/*
 			 * Read the current contents of the byte/word/dword containing
 			 * the field, and merge with the new field value.