+/* Searches the bits in PATTERN from left to right starting from
+ just beyond bit OFFSET for one or more 1-bits. If any are
+ found, sets *START to the bit index of the first and *WIDTH to
+ the number of contiguous 1-bits and returns true. Otherwise,
+ returns false.
+ This implementation is designed to be obviously correct, not
+ to be efficient. */
+static bool
+prev_region (unsigned int pattern, unsigned int offset,
+ unsigned long int *start, unsigned long int *width)
+{
+ unsigned int i;
+
+ assert (offset <= UINT_BIT);
+ for (i = offset; i-- > 0; )
+ if (pattern & (1u << i))
+ {
+ *start = i;
+ *width = 1;
+ while (i-- > 0 && pattern & (1u << i))
+ {
+ ++*width;
+ --*start;
+ }
+ return true;
+ }
+ return false;
+}
+